Polyphenylene sulfide film, laminated film, battery electrode, and battery

Abstract

The purpose of the present invention is to provide a polyphenylene sulfide film and a laminated film suitable for manufacturing a battery electrode excellent in productivity (specifically, battery productivity) and battery life. Another purpose of the present invention is to provide a battery electrode and a battery. The polyphenylene sulfide film contains a polyphenylene sulfide resin, has a thickness of 0.2-30 μm, and has an inclination of an orientation angle of 3.2° or less as measured using a microwave transmission molecular orientation meter. The laminated film includes the polyphenylene sulfide film and a metal thin film. The battery electrode includes the laminated film and an electrode material. The battery includes the battery electrode.

Description

Polyphenylene sulfide film, laminated film, battery electrodes, battery

[0001] This invention relates to a polyphenylene sulfide film, a laminated film, a battery electrode, and a battery.

[0002] In recent years, with the miniaturization of electronic devices, there has been a demand for smaller batteries installed in these devices. Along with this miniaturization, there is a demand for increased battery capacity and longer battery life. Examples of electronic devices include smartphones, tablets, and battery systems installed in electric vehicles. The batteries are primarily rechargeable batteries, such as lithium-ion rechargeable batteries. Conventional batteries, for example, use a metal foil with a thickness of 10 to 30 μm as the electrode substrate, and have electrodes formed by laminating electrode material on the metal foil, overlapping these electrodes via a sheet-like separator, and winding them together to store the electrolyte internally.

[0003] As an alternative to metal, Patent Documents 1 and 2 disclose electrodes in which a conductive thin film layer, such as a metal, is provided on the surface of a biaxially oriented polyester film, which has excellent mechanical properties and dimensional stability.

[0004] JP-A-10-40919 JP-A 10-40920

[0005] However, polyester film has the drawback of having low resistance to electrolytes, which shortens battery life.

[0006] The object of the present invention is to provide polyphenylene sulfide films and laminated films suitable for manufacturing battery electrodes with excellent productivity (specifically, battery productivity) and battery life. The present invention also aims to provide battery electrodes and batteries with excellent productivity (specifically, battery productivity) and battery life.

[0007] The present invention provides the following embodiments: [Claim 1] A polyphenylene sulfide film comprising a polyphenylene sulfide resin, having a thickness of 0.2 μm or more and 30 μm or less, and having an orientation angle inclination of 3.2° or less as measured using a microwave transmission molecular orientation meter. [Claim 2] The polyphenylene sulfide film according to Claim 1, wherein the tensile breaking strength in a first in-plane direction and in a second direction perpendicular to the first direction in the plane are both 90 MPa or more, and the plane orientation degree ΔP is 0.119 or less. [Claim 3] The polyphenylene sulfide film according to Claim 1 or Claim 2, having an NZ coefficient of 0.6 or more and 2.5 or less, preferably 0.6 or more and 2.0 or less. [Claim 4] The polyphenylene sulfide film according to any one of Claims 1 to 3, having a crystallinity of 25% or more, preferably 25.5% or more as measured by a differential scanning calorimeter (DSC). [Item 5] A polyphenylene sulfide film according to any one of Items 1 to 4, wherein the tensile elongation at break in a first direction in the plane and in a second direction perpendicular to the first direction in the plane are both 50% or more, and the ratio of the tensile elongation at break in the first direction to the tensile elongation at break in the second direction is 1.5 or more. [Item 6] A polyphenylene sulfide film according to any one of Items 1 to 5, wherein the polyphenylene sulfide film is a polyphenylene sulfide film that has been biaxially stretched by sequential biaxial stretching, and the crystallization temperature of the polyphenylene sulfide film after uniaxial stretching and before biaxial stretching is 104°C or higher. [Item 7] A polyphenylene sulfide film according to any one of Items 1 to 6, used for manufacturing electrodes for batteries. [Item 8] A polyphenylene sulfide film according to any one of Items 1 to 7, wherein the NZ coefficient is 1.8 or less, or 1.5 or less. [Item 9] A polyphenylene sulfide film according to any one of items 1 to 8, wherein the NZ coefficient is 0.7 or greater, or 0.8 or greater. [Item 10] A polyphenylene sulfide film according to any one of items 1 to 9, wherein the degree of plane orientation ΔP is 0.115 or less, or 0.110 or less. [Item 11] A polyphenylene sulfide film according to any one of items 1 to 10, wherein the degree of plane orientation ΔP is 0.050 or greater, or 0.055 or greater.[Item 12] A polyphenylene sulfide film according to any one of items 1 to 11, wherein the degree of plane orientation ΔP is 0.060 or greater, or 0.105 or less. [Item 13] A polyphenylene sulfide film according to any one of items 1 to 12, wherein the tilt of the orientation angle is 3.1° or less, or 3.0° or less. [Item 14] A polyphenylene sulfide film according to any one of items 1 to 13, wherein the tilt of the orientation angle is 2.5° or less, or 0.3° or greater. [Item 15] A polyphenylene sulfide film according to any one of items 1 to 14, wherein the tilt of the orientation angle is 0.01° or greater, or 0.1° or greater. [Item 16] A polyphenylene sulfide film according to any one of items 1 to 15, comprising inert particles, wherein the inert particles are preferably calcium carbonate particles. [Item 17] A polyphenylene sulfide film according to any one of items 1 to 16, wherein the melting point of the polyphenylene sulfide resin is 260°C or higher, or 270°C or higher. [Item 18] A polyphenylene sulfide film according to any one of items 1 to 19, wherein the number average molecular weight of the polyphenylene sulfide resin is 5,000 or more and 20,000 or less, or 8,000 or more and 15,000 or less. [Item 19] A polyphenylene sulfide film according to any one of items 1 to 18, wherein the thickness is 23 μm or less, or 20 μm or less. [Item 20] A polyphenylene sulfide film according to any one of items 1 to 19, wherein the thickness is 0.5 μm or more, or 3 μm or more. [Item 21] A polyphenylene sulfide film according to any one of items 1 to 20, wherein the thickness is 7 μm or more, or 10 μm or more. [Clause 22] A polyphenylene sulfide film according to any one of Clauses 1 to 21, wherein the polyphenylene sulfide film is biaxially oriented. [Clause 23] A polyphenylene sulfide film according to any one of Clauses 2 to 22, wherein the first direction is the MD direction and the second direction is the TD direction. [Clause 24] A laminated film comprising a polyphenylene sulfide film according to any one of Clauses 1 to 23 and a thin metal film provided on at least one surface of the polyphenylene sulfide film. [Clause 25] A laminated film according to Clause 24, wherein the thickness of the thin metal film is 1 nm to 1000 nm, or 10 nm to 1000 nm.[Clause 26] A laminated film according to Clause 24 or 25, used as an electrode film for a secondary battery. [Clause 27] A battery electrode comprising a laminated film according to any one of Clauses 24 to 26 and an electrode material provided on a thin metal film of the laminated film. [Clause 28] A battery electrode according to Clause 27, wherein the electrode material comprises at least one of lithium cobalt oxide and graphite. [Clause 29] A battery comprising the battery electrode according to Clause 27 or 28.

[0008] The present invention can provide polyphenylene sulfide films and laminated films suitable for manufacturing battery electrodes with excellent productivity and battery life. The present invention can also provide battery electrodes and batteries with excellent productivity and battery life.

[0009] Hereafter, the MD direction, or Machine Direction, may be referred to as the longitudinal direction. In other words, the MD direction and the longitudinal direction will be used as synonyms. The MD direction corresponds to an example of the "first direction" of the present invention. The TD direction, or Transverse Direction, may be referred to as the width direction. In other words, the TD direction and the width direction will be used as synonyms. The TD direction corresponds to an example of the "second direction" of the present invention.

[0010] Hereafter, extension in the MD direction may be referred to as longitudinal extension, and extension in the TD direction may be referred to as transverse extension.

[0011] Hereafter, the area ratio may be referred to as the total stretching ratio. The area ratio means the product of the first-stage stretching ratio (i.e., the first-axis stretching ratio) and the second-stage stretching ratio (i.e., the second-axis stretching ratio).

[0012] Hereafter, the refractive index in the MD direction may be referred to as nx, or refractive index nx. The refractive index in the TD direction may be referred to as ny, or refractive index ny. The refractive index in the thickness direction may be referred to as nz, or refractive index nz.

[0013] A polyphenylene sulfide film according to an embodiment of the present invention (hereinafter sometimes simply referred to as "the polyphenylene sulfide film of the present invention") contains a polyphenylene sulfide resin, has a thickness of 0.2 μm or more and 30 μm or less, and has an orientation angle tilt of 3.2° or less as measured using a microwave transmission type molecular orientation meter. Since the orientation angle tilt is 3.2° or less, it is possible to improve the productivity of batteries and improve the lifespan of batteries. This will be explained below. In the range where the orientation angle tilt is 45° or less, the larger the orientation angle tilt, the greater the tilt of the main orientation direction of the molecular chains from the stretching direction, and therefore the orientation direction of the molecular chains in the plane becomes uneven. For this reason, relaxation stress is likely to occur in multiple directions, including oblique directions in the plane, when heated, and as a result, uneven thermal shrinkage and local deformation of the film are likely to occur. In contrast, the polyphenylene sulfide film of the present invention has an orientation angle of 3.2° or less, which makes it possible to align the direction of recovery stress during heating. Therefore, it is possible to reduce wrinkles that may occur due to the heat applied to the polyphenylene sulfide film during the manufacture of battery electrodes, that is, wrinkles that may occur due to thermal shrinkage (hereinafter sometimes referred to as "shrinkage wrinkles"), and local deformation. For this reason, the polyphenylene sulfide film of the present invention can improve the productivity of batteries and extend their lifespan. The orientation angle can be adjusted, for example, by the ratio of the first-stage stretching ratio to the second-stage stretching ratio, specifically by the ratio of the transverse stretching ratio to the longitudinal stretching ratio. The polyphenylene sulfide film of the present invention will be described in detail below.

[0014] The polyphenylene sulfide film of the present invention contains a polyphenylene sulfide (PPS) resin. The polyphenylene sulfide film of the present invention can be used, for example, as a substrate for battery electrodes (hereinafter sometimes referred to as "electrode substrate"). A battery has a structure formed by winding together electrodes, for example, with a sheet-like separator in between, and stores an electrolyte inside. The battery can mainly be a secondary battery, for example, a lithium-ion secondary battery. The battery is mounted on, for example, an electronic device. Electronic devices are, for example, battery devices mounted on smartphones, tablets, and electric vehicles. A battery made using the polyphenylene sulfide film of the present invention can have improved battery capacity because the electrode substrate is thin. Because the polyphenylene sulfide film of the present invention contains a polyphenylene sulfide resin, it can have a high melting peak temperature and low thermal shrinkage (i.e., dimensional stability) as an electrode substrate. Furthermore, in terms of resistance to electrolytes, the polyphenylene sulfide film of the present invention is superior to conventional polyethylene terephthalate films because it contains polyphenylene sulfide resin. In addition, when the polyphenylene sulfide film of the present invention is a biaxially oriented polyphenylene sulfide film, it is possible to prevent or reduce short circuits due to thermal deformation of the electrode substrate, thereby improving battery life. Moreover, batteries made using the polyphenylene sulfide film of the present invention can be lighter than conventional products using metal foil as the electrode substrate, thereby improving gravimetric energy density.

[0015] In the present invention, the thickness of the polyphenylene sulfide film is preferably 0.2 μm or more and 30 μm or less. More preferably, the thickness is 0.2 μm or more and 23 μm or less. Having such a film thickness makes it possible to improve the energy density of the energy storage element, particularly the volumetric energy density, when used as a base film for the electrodes of the energy storage element. It can also provide bending resistance. If a film thicker than the upper limit is used as the electrode base, it becomes thicker than conventional metal foil, and it may not be possible to improve the energy density of the energy storage element, particularly the volumetric energy density. On the other hand, if the film thickness is so thin that it falls below the lower limit, it becomes extremely difficult to manufacture the film. For this reason, from the viewpoint of improving the energy density of the energy storage element, particularly the volumetric energy density, and the efficiency of film manufacturing, the present invention preferably has the above thickness. The film thickness is more preferably 0.2 μm or more and 20 μm or less, even more preferably 0.2 μm or more and 12 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less. The polyphenylene sulfide film of the present invention may have a single-layer structure or a structure of two or more layers.

[0016] In the present invention, the refractive index nx in the MD direction of the polyphenylene sulfide film is preferably 1.750 or higher. More preferably, the refractive index nx is 1.760 or higher, even more preferably 1.770 or higher, and particularly preferably 1.775 or higher. On the other hand, the refractive index nx is preferably 1.830 or lower. More preferably, the refractive index nx is 1.800 or lower, even more preferably 1.785 or lower, and particularly preferably 1.780 or lower. These upper and lower limits can be combined as appropriate; for example, the refractive index nx is 1.750 or higher and 1.830 or lower.

[0017] In the present invention, the refractive index ny in the TD direction of the polyphenylene sulfide film is preferably 1.830 or higher. More preferably, the refractive index ny is 1.860 or higher, even more preferably 1.870 or higher, and particularly preferably 1.880 or higher. On the other hand, the refractive index ny is preferably 1.930 or lower. More preferably, the refractive index ny is 1.900 or lower, even more preferably 1.880 or lower, and particularly preferably 1.870 or lower. Furthermore, these upper and lower limits can be combined as appropriate; for example, the refractive index ny is 1.830 or higher and 1.930 or lower.

[0018] In the present invention, the refractive index nz in the thickness direction of the polyphenylene sulfide film is preferably 1.720 or higher. More preferably, the refractive index nz is 1.730 or higher, even more preferably 1.740 or higher, and particularly preferably 1.750 or higher. On the other hand, the refractive index nz is preferably 1.830 or lower. More preferably, the refractive index nz is 1.820 or lower, even more preferably 1.810 or lower, and particularly preferably 1.800 or lower. Furthermore, these upper and lower limits can be combined as appropriate; for example, the refractive index nz is 1.720 or higher and 1.83 or lower.

[0019] Furthermore, the plane orientation degree ΔP of the polyphenylene sulfide film in the present invention is preferably 0.119 or less. More preferably, the plane orientation degree ΔP is 0.115 or less, even more preferably 0.110 or less, and particularly preferably 0.105 or less. On the other hand, the plane orientation degree ΔP is preferably 0.045 or more. More preferably, the plane orientation degree ΔP is 0.050 or more, even more preferably 0.055 or more, and particularly preferably 0.060 or more. These upper and lower limits can be combined as appropriate; for example, the plane orientation degree ΔP is 0.045 or more and 0.119 or less. Within this range, the workability of battery production by lamination and winding of electrode materials is improved. In particular, when the plane orientation degree ΔP is 0.119 or less, it is possible to prevent problems such as breakage during battery production and to improve battery life. The plane orientation degree ΔP is expressed by the following formula: ΔP = (nx + ny) / 2 - nz

[0020] In the present invention, the tilt of the orientation angle measured using a microwave transmission type molecular orientation meter (MOA) for the polyphenylene sulfide film is preferably 3.2° or less. More preferably, the tilt of the orientation angle is 3.1° or less, even more preferably 3.0° or less, and particularly preferably 2.5° or less. Within this range, shrinkage wrinkles during post-processing are less likely to occur, preventing problems and thus improving battery productivity. From the viewpoint of manufacturing cost, the tilt of the orientation angle is preferably 0.01° or more. More preferably 0.1° or more. The above upper and lower limits can be combined as appropriate, and the tilt of the orientation angle is, for example, 0° or more and 3.2° or less. In order to control the tilt of the orientation angle to the above-mentioned specific value, it is preferable to control the ratio of the first-stage stretching ratio to the second-stage stretching ratio (first-stage stretching ratio / second-stage stretching ratio). The first-stage stretching is preferably transverse stretching, and the second-stage stretching is preferably longitudinal stretching. When the first stage stretching is transverse stretching and the second stage stretching is longitudinal stretching (hereinafter sometimes referred to as "TM stretching"), the ratio of the first stage stretching ratio to the second stage stretching ratio is preferably, for example, 1.30 to 2.00, and more preferably 1.30 to 1.80. The temperature during the first stage stretching is preferably, for example, 80°C to 120°C. The temperature during the second stage stretching is also preferably, for example, 80°C to 120°C. Even in the case of TM stretching, or when the first stage stretching is longitudinal stretching and the second stage stretching is transverse stretching (hereinafter sometimes referred to as "MT stretching"), it is preferable that the absolute value of the difference between the second stage stretching temperature and the first stage stretching temperature is 9°C or less. This makes it possible to avoid or reduce an excessively large difference between the physical properties of the polyphenylene sulfide film in the direction of the first stage stretching and the physical properties of the film in the direction of the second stage stretching. In both TM and MT stretching, it is preferable that the stretching temperature for longitudinal stretching is higher than the stretching temperature for transverse stretching.

[0021] The NZ coefficient of the polyphenylene sulfide film of the present invention is preferably 0.6 or more and 2.5 or less. The NZ coefficient is a value obtained by |ny-nz| / |ny-nx|. The upper limit of the NZ coefficient is more preferably 2.0, even more preferably 1.8, and particularly preferably 1.5. The lower limit of the NZ coefficient is more preferably 0.7, and even more preferably 0.8. These upper and lower limits can be combined as appropriate, and the NZ coefficient is, for example, more preferably 0.8 or more and 1.8 or less, and even more preferably 0.8 or more and 1.5 or less. The closer the NZ coefficient is to 1.0, the higher the uniaxial orientation. If the slope of the orientation angle is large and the NZ coefficient exceeds 2.0, tensile stress and shear stress compete during slitting, and crack propagation tends to meander and accelerate, leading to instability of the cutting line. On the other hand, by reducing the inclination of the orientation angle and controlling the NZ coefficient to be between 0.6 and 2.5, the skewness of the in-plane orientation is suppressed, and the direction of stress concentration during cutting is made constant. As a result, fluctuations in the cutting load are reduced, burrs and fuzzing at the film edge are suppressed, and good slitting suitability is obtained. In order to control the NZ coefficient to a specific range, for example, the ratio of the first-stage stretching ratio to the second-stage stretching ratio, the total stretching ratio, and the stretching temperature can be set appropriately. For example, the lower the total stretching ratio and the higher the stretching temperature, the lower the NZ coefficient can be obtained.

[0022] Furthermore, in the polyphenylene sulfide film of the present invention, the tensile breaking strength in the first direction and the second direction is preferably 90 MPa or more, and more preferably 100 MPa or more. In the polyphenylene sulfide film of the present invention, the tensile breaking strength in the first direction and the second direction is preferably 300 MPa or less, and more preferably 250 MPa or less. These upper and lower limits can be combined as appropriate, for example, the tensile breaking strength in the first direction and the second direction is 90 MPa or more and 300 MPa or less, respectively. Within this range, the workability of battery production by lamination and winding of electrode materials is good. In particular, at 90 MPa or more, it is possible to prevent problems such as breakage during battery production and to improve battery life. Note that the tensile breaking strength in the first direction and the second direction may be about the same or different within the above range. For example, the tensile breaking strength in the first direction and the second direction may be 110 MPa or more, or 120 MPa or more, respectively.

[0023] Here, the first direction is any direction in the plane of the polyphenylene sulfide film of the present invention, preferably the MD direction. On the other hand, the second direction is a direction perpendicular to the first direction in the plane, preferably the TD direction.

[0024] Next, in the polyphenylene sulfide film of the present invention, the tensile elongation at break in the first direction and the second direction is preferably 50% or more, and more preferably 55% or more. The tensile elongation at break in the first direction and the second direction is preferably 200% or less, and more preferably 190% or less. These upper and lower limits can be combined as appropriate; for example, the tensile elongation at break in the first direction and the second direction is 50% or more and 200% or less, respectively. Within this range, the workability of battery production by lamination and winding of electrode materials is good. In particular, at 50% or more, it is possible to prevent problems such as breakage from occurring during battery production. Next, in the polyphenylene sulfide film of the present invention, the ratio of the tensile elongation at break in the first direction to the tensile elongation at break in the second direction (i.e., tensile elongation at break in the first direction / tensile elongation at break in the second direction; hereinafter sometimes referred to as "ELAS-MD / ELAS-TD") is preferably 1.5 or more, and more preferably 2.0 or more. ELAS-MD / ELAS-TD is preferably 3.5 or less, and more preferably 3.0 or less. These upper and lower limits can be combined as appropriate; for example, ELAS-MD / ELAS-TD is between 1.5 and 3.5. Within this range, the workability of battery production by laminating and winding electrode materials is good. In particular, at 1.5 or higher, it is possible to prevent problems such as breakage during battery production.

[0025] The tensile modulus in the first direction and the tensile modulus in the second direction may each be, for example, 1500 MPa or more, or 2500 MPa or more. On the other hand, the tensile modulus in the first direction and the tensile modulus in the second direction may each be, for example, 5000 MPa or less, or 4500 MPa or less. These upper and lower limits can be combined as appropriate; for example, the tensile modulus in the first direction and the tensile modulus in the second direction may each be between 1500 MPa and 4500 MPa. The ratio of the tensile modulus in the first direction to the tensile modulus in the second direction (i.e., tensile modulus in the first direction / tensile modulus in the second direction) may be, for example, 1.5 or less, or 1.0 or less. It may also be 0.5 or more. These upper and lower limits can be combined as appropriate; for example, this ratio may be between 0.5 and 1.5.

[0026] The polyphenylene sulfide film of the present invention preferably has a heat shrinkage rate of 4% or less in the first and second directions at 180°C for 30 minutes. More preferably, it is 3.5% or less, and more preferably 3% or less. If the heat shrinkage rate is too high, excessive thermal deformation of the electrodes of the secondary battery may occur when heat is generated due to internal resistance, which may cause a short circuit. The heat shrinkage rates in the first and second directions may be similar or different. The heat shrinkage rate is measured by the following method: A test piece with a width of 10 mm and a length of 250 mm is cut from the polyphenylene sulfide film. A pair of marks (i.e., a pair of gauge marks) are made at 200 mm intervals along the length of this test piece, and the distance between the gauge marks is measured under a tension of 5 gf. This test piece is heat-treated at 180°C for 30 minutes under no load, and the distance between the gauge marks is measured under a tension of 5 gf. The test piece is then heat-treated at 180°C for 30 minutes, and the distance between the gauge marks is measured under a tension of 5 gf. From these measurement results, the heat shrinkage rate is calculated using the following formula. Heat shrinkage rate (%) = {(A - B) / A} × 100 Here, A is the gauge length before heat treatment, and B is the gauge length after heat treatment. Using this procedure, the heat shrinkage rates in the first and second directions are determined.

[0027] The polyphenylene sulfide film of the present invention can have its surface roughened by adding inert particles (inert particles) to the polymer as a surface roughening agent, to the extent that it does not impair the effects of the present invention. In other words, the polyphenylene sulfide film of the present invention may contain inert particles. The surface roughness of the film is preferably such that the center plane average roughness SRa is 5 nm or more and 70 nm or less, and more preferably 6 nm or more and 65 nm or less. Furthermore, the ten-point average roughness SRz is preferably 200 nm or more and 950 nm or less, and more preferably 250 nm or more and 900 nm or less. If SRa is less than 5 nm and SRz is less than 200 nm, the transportability of the film is significantly reduced. Furthermore, if SRa exceeds 70 nm and SRz exceeds 950 nm, it is difficult to obtain proper adhesion with the cooling roll during vapor deposition. Therefore, by having the above roughness, the present invention can further improve transportability and provide good proper adhesion with the cooling roll during vapor deposition.

[0028] Furthermore, it is preferable that the surface roughness satisfies the following formula (2). By satisfying the following formula, the air release when winding the polyphenylene sulfide film of the present invention onto a roll is improved, and wrinkles and folds on the roll can be suppressed. 10 ≤ SRz / SRa ≤ 50 ... (2)

[0029] The above formula (2) can take the following forms: 10 ≤ SRz / SRa ≤ 40, or 12 ≤ SRz / SRa ≤ 38. By taking such values, the air release properties when winding the polyphenylene sulfide film of the present invention onto a roll are further improved, and wrinkles and folds on the roll can be suppressed more effectively.

[0030] The roughening agent is preferably fine particles with an average particle size of 0.05 μm to 5 μm. Preferably, the fine particles are inert particles. The amount added is preferably 500 ppm to 20,000 ppm, more preferably 1,000 ppm to 15,000 ppm, and even more preferably 1,500 ppm to 10,000 ppm. Here, ppm refers to mass ppm.

[0031] Examples of roughening agents include calcium carbonate, magnesium carbonate, barium carbonate, barium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon dioxide (silica), titanium dioxide, kaolin, talc, carbon black, silicon nitride, boron nitride, and crosslinked polymer fine particles.

[0032] The polyphenylene sulfide film of the present invention preferably has a melting peak temperature of 250°C or higher, more preferably 260°C or higher, and even more preferably 270°C or higher in DSC temperature measurement. The melting peak temperature is, for example, 300°C or lower. By having a melting peak temperature of 250°C or higher, for example, when used in a secondary battery, thermal deformation of the electrodes can be suppressed or reduced when heat is generated due to internal resistance, and short circuits can also be prevented or reduced.

[0033] The polyphenylene sulfide resin is preferably a homopolymer, but may also be a copolymer. Alternatively, it may be a polymer blend consisting of two or more of these homopolymers and / or copolymers.

[0034] The melting peak temperature (hereinafter sometimes referred to as the "melting point") of polyphenylene sulfide resin, specifically the melting peak temperature in DSC temperature rise measurement, is preferably 250°C or higher, more preferably 260°C or higher, and even more preferably 270°C or higher. The melting peak temperature of polyphenylene sulfide resin is, for example, 300°C or lower. A melting peak temperature of 250°C or higher allows for suppression or reduction of thermal deformation of electrodes when heat is generated due to internal resistance, for example, when used in a secondary battery, and also prevents or reduces short circuits.

[0035] The number-average molecular weight of the polyphenylene sulfide resin may be, for example, between 5,000 and 20,000, or between 8,000 and 15,000. The number-average molecular weight of the polyphenylene sulfide resin is a value calculated in polystyrene equivalent using gel permeation chromatography (GPC).

[0036] In the polyphenylene sulfide film of the present invention, the content of the polyphenylene sulfide resin is preferably 98% by mass or more, more preferably 99% by mass or more.

[0037] The polyphenylene sulfide film of the present invention can be produced according to conventionally known methods. For example, after sufficiently drying a raw material polymer under predetermined conditions, the raw material polymer is supplied to a melt extrusion apparatus (represented by an extruder), and heated and melted at a temperature not lower than the melting point (Tm: °C) of the polymer, particularly at a temperature not lower than Tm and not higher than (Tm + 70) °C. In this extrusion step, the raw material polymer is melt-kneaded so as to be uniform, and the degree of melt-kneading is adjusted.

[0038] Next, the melt-kneaded polymer is extruded into a sheet from a slit-shaped die lip, and quenched and solidified on a rotating cooling drum to obtain a substantially amorphous unstretched sheet. In this case, in order to enhance the adhesion to the rotating cooling drum and improve the surface flatness (planarity and smoothness) of the sheet, an electrostatic charge application adhesion method and / or a liquid application adhesion method is preferably employed. The electrostatic charge application adhesion method is a method in which a DC voltage is applied to a linear electrode stretched in a direction orthogonal to the flow of the sheet extruded from a die to apply an electrostatic charge to the surface (non-drum side) of the sheet, and this effect improves the adhesion between the sheet and the rotating cooling drum. The liquid application adhesion method is a method in which a liquid is uniformly applied to all or part of the surface of the rotating cooling drum (for example, portions that contact both end portions of the sheet) to improve the adhesion between the sheet and the rotating cooling drum. In the present invention, both methods may be used in combination as needed. In addition, as a method for producing a substantially amorphous unstretched sheet, an inflation casting method or a casting method can also be employed.

[0039] The unstretched sheet obtained in this manner is then stretched biaxially to obtain a biaxially stretched film. A sequential biaxial stretching method (tenter method) can be used as this stretching method. As stretching conditions for the sequential biaxial stretching method, the unstretched sheet is stretched in the TD direction at a temperature of (Tg-10)°C or higher and (Tg+70)°C or lower to a draw ratio of 3.2 times to 6.0 times, preferably 3.3 times to 5.5 times. In order to set the temperature-rising crystallization temperature of the film after uniaxial stretching and before biaxial stretching within the temperature range described below, this temperature (that is, the first-stage stretching temperature) is preferably 95°C or higher. Similarly, the first-stage stretching temperature is preferably 115°C or lower. Next, stretching is performed in the MD direction orthogonal to the first stage at a temperature of Tg or higher and (Tg+70)°C or lower to a draw ratio of 1.5 times to 6 times, preferably 1.8 times to 5.5 times. Furthermore, a method in which stretching in at least one of the two axial directions is performed in multiple stages of two or more steps can also be used. In such cases, it is also desirable that the final draw ratio falls within the range described above. Further, after performing intermediate heat setting after the second-stage stretching, stretching may be performed again in the same direction as the first stage and / or the same direction as the second stage. The area draw ratio of biaxial stretching is preferably 9.0 times or less, more preferably 8.5 times or less, and still more preferably 8.2 times or less. The area draw ratio may be, for example, 6.0 times or more.

[0040] The draw ratio in the TD direction is preferably set in a range of 1.3 times to 2.0 times relative to the draw ratio in the MD direction.

[0041] In order to perform the second-stage stretching such that the difference in draw ratio relative to the draw ratio in the first-stage stretching direction falls within the above range, the temperature-rising crystallization temperature of the polyphenylene sulfide film after uniaxial stretching and before biaxial stretching is preferably within the following temperature range. That is, the temperature-rising crystallization temperature is preferably 104°C or higher, more preferably 105°C or higher. Further, the temperature-rising crystallization temperature is preferably 115°C or lower, more preferably 110°C or lower. For example, the temperature-rising crystallization temperature is preferably 104°C or higher and 115°C or lower. The temperature-rising crystallization temperature refers to the temperature at which crystallization occurs when the temperature of a resin molded in a state of insufficient crystallization is increased.

[0042] It is preferable to perform heat fixing on the biaxially oriented film obtained in this manner. The heat fixing temperature is preferably 100°C to 200°C, and more preferably 110°C to 290°C. The heat fixing temperature may be, for example, 180°C or lower, or 170°C or lower. This heat fixing is preferably carried out for 1 second to 10 minutes. In this case, the heat fixing may be carried out under a limited shrinkage or elongation of 20% or less, or under a constant length, and may be carried out in two or more stages.

[0043] The polyphenylene sulfide film of the present invention preferably has a density of 1.340 g / dL or higher. For example, the density is 1.40 g / dL or lower. When the density is within this range, crystallization is sufficiently promoted, and therefore thermal shrinkage can be suppressed.

[0044] In the polyphenylene sulfide film of the present invention, the degree of crystallinity measured by differential scanning calorimetry (DSC) is preferably 25% or more, more preferably 25.5% or more. Furthermore, the degree of crystallinity is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. The upper and lower limits can be combined as appropriate, and the degree of crystallinity is preferably, for example, 25% or more and 50% or less. A degree of crystallinity of 25% or more improves the stability and durability of the film's physical properties, thereby extending the battery's lifespan. On the other hand, a degree of crystallinity of 50% or less prevents the film from becoming excessively rigid, and therefore prevents an excessive decrease in the workability of battery production by winding.

[0045] The polyphenylene sulfide film of the present invention may be surface-treated to improve its adhesion to metal thin films. The surface treatment method is not particularly limited, but preferred examples include coating of an adhesive layer, corona treatment, plasma treatment, etc.

[0046] The polyphenylene sulfide film of the present invention can be used to manufacture battery electrodes, is suitably used to manufacture secondary battery electrodes, and is more suitably used to manufacture lithium-ion secondary battery electrodes. In order to use the polyphenylene sulfide film of the present invention as a film for secondary battery electrodes, a thin metal film can be formed on at least one of its surfaces. Examples of metals for forming the thin metal film include aluminum, nickel, gold, silver, copper, and cadmium. The thickness of the thin metal film is usually 1 nm to 1000 nm, but is preferably 10 nm to 1000 nm in order to suppress internal resistance heating of the battery. Examples of methods for forming the thin metal film include vacuum deposition, electroplating, and sputtering.

[0047] An embodiment of the present invention comprises a polyphenylene sulfide film of the present invention and a metal thin film provided on at least one of the two surfaces of the polyphenylene sulfide film.

[0048] The laminated film of the present invention can be used as a battery electrode by laminating an electrode material onto its metal thin film surface. Conventional electrode materials such as lithium cobalt oxide and graphite can be used. Furthermore, a battery can be manufactured using this battery electrode by conventional methods. For example, when manufacturing a lithium-ion secondary battery, a film for secondary battery electrodes having a copper thin film formed by sputtering, coated with lithium cobalt oxide, is used as the positive electrode, and a film for secondary battery electrodes having an aluminum vapor-deposited film, coated with graphite, is used as the negative electrode. A separator made of polyethylene microporous membrane is then interposed between the positive and negative electrodes during winding, and an organic solvent containing a dissolved lithium salt is used as the electrolyte to form a lithium-ion secondary battery.

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. The various physical properties and characteristics in the present invention were measured and defined as follows.

[0050] [Measurement or Evaluation Method] (1) Film thickness A film was sandwiched between a spindle detector (K107C, manufactured by Anritsu Electric Co., Ltd.), and the thickness was measured at 10 different positions using a digital differential electronic micrometer (K351, manufactured by Anritsu Electric Co., Ltd.), and the average value was calculated as the film thickness.

[0051] (2) Tensile properties A test piece with a width of 10 mm and a length of 150 mm was cut out from the film. The test piece was pulled with a distance between chucks of 100 mm at a speed of 100 mm / min using a precision universal testing machine (Autograph AGS-X, manufactured by Shimadzu Corporation). The stress (MPa) when the test piece broke was determined as the tensile breaking strength. The percentage (%) of the increase in the distance between chucks when the test piece broke relative to the initial distance between chucks (i.e., 100 mm) was determined as the tensile elongation at break. Here, the "increase in the distance between chucks when the test piece broke" is the difference between the distance between chucks at break and the initial distance between chucks (i.e., distance between chucks at break − initial distance between chucks). The maximum value of the slope of the stress-strain curve was determined as the tensile modulus of elasticity.

[0052] (3) Refractive index Using a laser refractometer (Model 2010 Prism Coupler) manufactured by Metricon, the center of one film was sandwiched under a pressure corresponding to the 40th scale of the built-in pressure gauge, measurement was performed with a laser beam of 633 nm wavelength, and a spectrum chart was obtained. On the obtained spectrum chart, the point where the detector output dropped sharply was read, and this value was taken as the refractive index. The in-plane orientation degree ΔP was calculated from the following formula based on the refractive index nx in the machine direction (hereinafter sometimes referred to as "nx １ "), the refractive index ny in the transverse direction (hereinafter sometimes referred to as "ny １ ") and the refractive index nz in the thickness direction: ΔP = (nx １ + ny １ ) / 2 − nz Birefringence (hereinafter sometimes referred to as "Δn") was calculated by the following formula: Δn = |nx １ − ny １ | The average refractive index of nx １ , ny １ and nz (hereinafter sometimes referred to as "nave") was also calculated. The NZ coefficient is |ny １ − nz| / |ny １-nx １ The value obtained using | was calculated.

[0053] (4) A 5 mg crystallization film was placed in a TA Instruments differential scanning calorimeter DSC250 and heated in a nitrogen gas stream at a heating rate of 10°C / min. The exothermic behavior associated with crystallization and the endothermic behavior associated with melting of the film were analyzed using first and second derivatives, and the temperature at which a peak or shoulder appeared was determined to obtain the heating crystallization energy Hc1 (unit: J / g) and the melting energy Hm (unit: J / g). Assuming that the melting heat energy of a perfect crystal is 146.2 J / g, the degree of crystallization was calculated using the following formula: Degree of crystallization = (Hm - Hc1) / 146.2 × 100

[0054] (5) Orientation Angle Tilt The orientation angle of the film and the tilt of the orientation angle were measured using a microwave transmission molecular orientometer (Oji Instruments MOA6004). Unlike (3) above, in this microwave transmission molecular orientometer, the refractive index that is maximum in each direction within the plane of the film is expressed as nx, and the refractive index in the direction perpendicular to the direction showing the maximum refractive index nx within the plane is expressed as ny. Here, in order to distinguish it from (3) above, the former (i.e., the maximum refractive index within the plane of the film) is expressed as nx ２ It is sometimes referred to as the latter (i.e., nx ２ (Refractive index in the direction perpendicular to the direction showing and in the plane) ２ It is sometimes referred to as the orientation angle of the film. The orientation angle of the film is this maximum refractive index (i.e., nx ２ This is the angle between the direction indicated by the TD direction and the MD direction. The slope of the orientation angle is the difference between 90° in the TD direction and the absolute value of the orientation angle, as shown by the following formula: Slope of orientation angle = 90° - |Orientation angle|

[0055] (6) Melting peak temperature (Tm), heating crystallization temperature 5 mg of polyphenylene sulfide resin was placed in a TA Instruments differential scanning calorimeter DSC250 and heated in a nitrogen gas stream at a heating rate of 10°C / min. The endothermic behavior associated with the melting of the film was analyzed using first and second derivatives, and the temperature at which a peak was observed was determined as the melting peak temperature (unit: °C). 5 mg of the film, after uniaxial stretching but before biaxial stretching, was similarly heated in a TA Instruments differential scanning calorimeter DSC250, and the exothermic behavior associated with the heating crystallization of the film was analyzed using first and second derivatives. The temperature at which a peak was observed was determined as the heating crystallization temperature (unit: °C).

[0056] (7) Battery Capacity Continuous discharge was performed on the lithium-ion secondary batteries manufactured using the method described below. If the amount of electricity discharged (i.e., discharge capacity) by the time the discharge voltage reached 80% of the rated value was 2100 mAh or more, it was judged as ○ (i.e. good), and if it was less than 2100 mAh, it was judged as × (i.e. poor).

[0057] (8) Productivity of battery manufacturing When manufacturing 100 lithium-ion secondary batteries using the method described below, the number of lithium-ion secondary batteries in which at least one of the fractures and wrinkles occurred from the coating of the electrode material to winding (i.e., winding the positive electrode material, separator, and negative electrode material while overlapping them) was counted. If the number was less than 9 (i.e. less than 9%), it was judged as ○ (i.e. good), and if the number was 10 or more (i.e. 10% or more), it was judged as × (i.e. poor).

[0058] (9) Battery life A repeated charge-discharge test was performed on lithium-ion secondary batteries manufactured using the method described below under conditions of 100°C. If the degradation cycle until a short circuit occurred in 10% of the total number of lithium-ion secondary batteries was 550 or more, it was judged as ○ (i.e. good); if it was 300 or more but less than 550, it was judged as △ (i.e. moderately good); and if it was less than 300, it was judged as × (i.e. poor).

[0059] (10) Slitting properties (processability) The cut surface of the film after slitting with a slitter, i.e., the cut end of the film divided into two equal parts, was observed with an optical microscope and evaluated according to the following criteria. ○: No bulging in the cross-section and no slitting debris is observed. △: There is bulging in the cross-section and a small amount of powdery or elongated slitting debris is observed. ×: There is bulging in the cross-section and powdery or elongated slitting debris is clearly observed.

[0060] (11) Overall Evaluation If all four items are marked with ○, the overall evaluation is ◎. If three of the four items are marked with ○ and one is marked with △, the overall evaluation is ○. If three of the four items are marked with ○ and one is marked with ×, the overall evaluation is △. If two or more of the four items are marked with ×, the overall evaluation is ×.

[0061] [Example 1] A masterbatch with a calcium carbonate particle concentration of 6000 ppm was prepared by melt-kneading a polyphenylene sulfide resin and calcium carbonate particles with an average particle size of 0.6 μm using a twin-screw extruder. The polyphenylene sulfide resin exhibited a Tg of 89°C, a Tm of 278°C, a number-average molecular weight Mn of 9000, and a melt viscosity of 235 Pa·s at 300°C with a shear rate of 122 / s. After drying and crystallizing this masterbatch, it was melt-extruded through a slit-shaped die set at a temperature of 315°C, and rapidly cooled and solidified on a rotating cooling drum with a surface temperature of 30°C using an electrostatic charge application adhesion method to obtain an unstretched sheet.

[0062] After preheating the unstretched sheet, it underwent sequential biaxial stretching: first, it was stretched 3.5 times in the width direction at a stretching temperature of 101°C, and second, it was stretched 2.0 times in the longitudinal direction at a stretching temperature of 105°C. Next, it was heat-set at 200°C for 30 seconds and cooled to room temperature to obtain a biaxially oriented film with a thickness of 20.4 μm. The measurement and evaluation results of the obtained biaxially oriented film are shown in Table 3.

[0063] Thin copper films were formed on both sides of this biaxially oriented film by sputtering, and lithium cobalt oxide was coated on top to form the positive electrode material. Aluminum vapor deposition was applied to both sides of the same biaxially oriented film, and graphite was coated on top to form the negative electrode material.

[0064] A lithium-ion secondary battery was fabricated by winding a separator made of polyethylene microporous membrane between the positive electrode material and the negative electrode material, and using a solution of lithium hexafluoride phosphate dissolved in a mixed solvent of ethylene carbonate / diethyl carbonate / ethyl acetate as the electrolyte.

[0065] The productivity, capacity, and lifespan of the obtained batteries during the series of processes are shown in Table 3.

[0066] [Example 2] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat setting temperature was set to 120°C. [Example 3] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat setting temperature was set to 160°C.

[0067] [Example 4] Film deposition and battery fabrication were carried out in the same manner as in Example 1, except that the heat-fixing temperature was set to 180°C.

[0068] [Example 5] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat-fixing temperature was set to 140°C and the film thickness was set to 11.6 μm by adjusting the extrusion amount.

[0069] [Example 6] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat-fixing temperature was set to 140°C, the stretching ratio and area magnification were changed, and the film thickness was adjusted to 10.3 μm by adjusting the extrusion amount.

[0070] [Example 7] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat-fixing temperature was set to 140°C, the stretching ratio and area magnification were changed, and the film thickness was adjusted to 9.7 μm by adjusting the extrusion amount.

[0071] [Comparative Example 1] After drying and crystallizing the masterbatch described above (see Example 1), it was melt-extruded through a slit-shaped die set at a temperature of 315°C, and rapidly cooled and solidified on a rotating cooling drum with a surface temperature of 30°C using an electrostatic charge application adhesion method to obtain an unstretched sheet.

[0072] After preheating the unstretched sheet, it underwent sequential biaxial stretching: first, it was stretched 3.0 times in the longitudinal direction at a stretching temperature of 110°C, and second, it was stretched 3.8 times in the width direction at a stretching temperature of 100°C. Next, it was heat-set at 200°C for 30 seconds and cooled to room temperature to obtain a biaxially oriented film with a thickness of 4.8 μm. The measurement and evaluation results of the obtained biaxially oriented film are shown in Table 3.

[0073] The battery was fabricated in the same manner as in Example 1, except that this biaxially oriented film was used. The evaluation results of the battery are shown in Table 3.

[0074] [Comparative Example 2] Film formation and battery fabrication were carried out in the same manner as in Comparative Example 1, except that the second stretching temperature was set to 98°C.

[0075] In this table, the stretching ratio refers to the ratio of the first-stage stretching ratio to the second-stage stretching ratio (i.e., first-stage stretching ratio / second-stage stretching ratio). In the stretching method column of this table, TM refers to sequential biaxial stretching, where stretching in the width direction is followed by stretching in the longitudinal direction. On the other hand, MT refers to sequential biaxial stretching, where stretching in the longitudinal direction is followed by stretching in the width direction.

[0076] The present invention can provide polyphenylene sulfide films, laminated films, battery electrodes, and batteries. Therefore, the present invention has industrial applicability.

Claims

1. A polyphenylene sulfide film containing polyphenylene sulfide resin, having a thickness of 0.2 μm or more and 30 μm or less, and having an orientation angle tilt of 3.2° or less as measured using a microwave transmission type molecular orientation meter.

2. The polyphenylene sulfide film according to claim 1, wherein the tensile breaking strength in a first in-plane direction and in a second direction perpendicular to the first direction in the plane are both 90 MPa or more, and the plane orientation degree ΔP is 0.119 or less.

3. The polyphenylene sulfide film according to claim 1, wherein the NZ coefficient is 0.6 or more and 2.5 or less.

4. The polyphenylene sulfide film according to claim 1, wherein the degree of crystallinity measured by differential scanning calorimeter (DSC) is 25% or more.

5. The polyphenylene sulfide film according to claim 1, wherein the tensile elongation at break in a first direction in the plane and in a second direction perpendicular to the first direction in the plane are both 50% or more, and the ratio of the tensile elongation at break in the first direction to the tensile elongation at break in the second direction is 1.5 or more.

6. The polyphenylene sulfide film according to claim 1, wherein the polyphenylene sulfide film is a polyphenylene sulfide film that has been biaxially stretched by sequential biaxial stretching, and the crystallization temperature of the polyphenylene sulfide film after uniaxial stretching and before biaxial stretching is 104°C or higher.

7. The polyphenylene sulfide film according to claim 1, used for manufacturing electrodes for batteries.

8. A laminated film comprising a polyphenylene sulfide film according to any one of claims 1 to 7 and a metal thin film provided on at least one surface of the polyphenylene sulfide film.

9. A battery electrode comprising a laminated film according to claim 8 and an electrode material provided on a metal thin film of the laminated film.

10. A battery comprising the battery electrode described in claim 9.

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