Biaxially oriented polyester film for thick vapor deposition, film for electrode of battery, and battery

Abstract

To reduce pin holes to endure processing tension using a metal vapor deposition film as an electrode substrate, further to provide a biaxially oriented polyester film for thick vapor deposition which improves resistance characteristic of an electrode sheet in order to improve battery performance such as high output and long life of a battery, and a film for an electrode of the battery using the same.SOLUTION: A biaxially oriented polyester film for thick vapor deposition satisfies the following (1)-(3). (1) A degree of crystallinity obtained by differential scan calorimetry is 30.0 to 50.0%. (2) An inherent viscosity (IV, dl / g) is 0.60 to 0.80. (3) A DEG (diethylene glycol) amount in the polyester film is 1.5 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polyester film for thick deposition, and a battery electrode film using the same. [Background technology]

[0002] In recent years, the promotion of renewable energy has become increasingly important as a measure to simultaneously reduce greenhouse gas emissions and ensure energy security. In particular, it is difficult to ensure stable output from solar and wind power generation because the amount of power generated depends on weather conditions, and lithium-ion secondary batteries are effectively used in renewable energy power generation facilities.

[0003] Recently, lithium-ion secondary batteries have started to be used in automobiles, including electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), and are also widely used in small electronic devices such as mobile phones, laptops, and portable music players. To miniaturize lithium-ion secondary batteries in line with the development of the portable electronic device market, it is necessary to improve their performance and reliability.

[0004] The electrodes used in these lithium-ion secondary batteries have the function of absorbing (storing) and releasing (releasing) lithium in both the positive and negative electrodes, and lithium ions move to the negative electrode during charging and to the positive electrode during discharging. Each electrode must be in contact with an electrolytic solution or a solid electrolyte to transfer lithium ions between the electrodes, and metal foils with a thickness of about 10 to 30 μm have conventionally been used as the substrate for the electrodes (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-054339 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in recent years, as the volumetric energy density has improved due to the increased capacity of lithium-ion secondary batteries, it has become necessary to improve the weight energy density by miniaturizing the batteries, and efforts are being made to make electrode substrates thinner. However, the conventional technology of thinning the substrate by rolling metal foil has posed issues such as the generation of pinholes that cause the coating liquid to leak through, or the substrate being too weak to withstand the processing tension, resulting in cuts or wrinkles.

[0007] In view of the above, the present invention provides a biaxially oriented polyester film for thick deposition in order to improve the resistance characteristics of the electrode sheet, and a battery electrode film using the same, by using a metal vapor deposition film as the electrode substrate, which has fewer pinholes and can withstand processing tension, and which leads to improved battery performance such as higher output and longer life. [Means for solving the problem]

[0008] As a result of extensive investigations aimed at solving the above problems, it was found that the above problems could be solved by using a biaxially oriented film having specific physical properties as a substrate film, which led to the present invention.

[0009] That is, a preferred embodiment of the biaxially oriented polyester film for thick deposition of the present invention and a battery electrode film using the same have the following configuration. 1. A biaxially oriented polyester film for thick deposition that satisfies the following (1) to (3). (1) The degree of crystallinity as determined by differential scanning calorimetry using the following method is 30.0 to 50.0%. <Measurement method> Measure by heating from 25°C to 300°C at a heating rate of 20°C / min. The degree of crystallinity (Χc) is calculated from the differential scanning calorimetry chart obtained using the heat of crystalline fusion (ΔHm) and the heat of cold crystallization (ΔHc) according to the following formula. Χc=(ΔHm-ΔHc) / ΔHm0 Here, ΔHm0 is 140.10 J / g, which is the heat of fusion of perfectly crystalline PET. (2) Intrinsic viscosity (IV, unit dl / g) is 0.60 to 0.80. (3) The amount of DEG (diethylene glycol) in the polyester film, as determined by the following method, is 1.5 mass% or less. <Measurement method> 1.0 g of polyester film is decomposed at 260°C using 2.5 mL of monoethanolamine containing 0.4% by mass of 1,6-hexanediol. Next, 10 mL of methanol is added and cooled, neutralized with terephthalic acid, centrifuged, and the supernatant is subjected to gas chromatography to measure the diethylene glycol (DEG) content. Note that since added components such as inorganic particles settle as insoluble matter during centrifugation, the settled components are filtered and mass measured, and the mass is subtracted from the measured sample mass to correct the measured sample mass. 2. The biaxially oriented polyester film for thick deposition according to 1., having a minute endothermic peak temperature (Tmeta) of 220°C or higher. 3. The biaxially oriented polyester film for thick deposition according to 1. or 2., wherein the biaxially oriented polyester film has a thickness of 1.5 to 15 μm. 4. A film for a battery electrode, which uses the biaxially oriented polyester film for thick deposition according to any one of 1. to 3. 5.4. An electrode film for a secondary battery. 6.5. An electrode film for a lithium-ion secondary battery. 7. A battery having the electrode film for a battery according to any one of 1 to 6. Effect of the Invention

[0010] According to the present invention, by using a metal-deposited film as an electrode substrate, it is possible to reduce pinholes and to withstand processing tension. Furthermore, it is possible to provide a biaxially oriented polyester film for thick deposition that can improve the resistance characteristics of an electrode sheet to improve battery performance such as high output and long life, and a battery electrode film using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below.

[0012] A preferred embodiment of the biaxially oriented polyester film for thick deposition of the present invention is a biaxially oriented polyester film for thick deposition that satisfies the following (1) to (3). (1) The crystallinity as determined by differential scanning calorimetry using the method described below is 30.0 to 50.0%. (2) Intrinsic viscosity (IV, unit dl / g) is 0.60 to 0.80. (3) The amount of DEG (diethylene glycol) in the polyester film, as determined by the method described below, is 1.5 mass% or less.

[0013] In this embodiment, the use of a metal-deposited film as the electrode substrate reduces pinholes and allows the electrode substrate to withstand processing tension. Furthermore, a biaxially oriented polyester film for thick deposition that can improve the resistance characteristics of an electrode sheet to improve battery performance such as high output and long life, and a battery electrode film using the same can be provided.

[0014] The biaxially oriented polyester film of the present invention is produced by stretching an unstretched resin sheet or film in two directions, the longitudinal direction and the transverse direction, and shows a biaxially oriented pattern by wide-angle X-ray diffraction. As a method for stretching in the biaxial directions, either a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used.

[0015] In the present invention, the term "thick deposition" refers to an application in which metal deposition of 0.5 μm or more is laminated on both sides or one side, and may be deposited multiple times on the same side. A vacuum process is used as a method for forming a metal deposition film. The vacuum process can be formed by vacuum deposition, sputtering, ion plating, plasma vapor phase epitaxy (CVD), etc. However, considering productivity, the vacuum deposition method is currently the most excellent. As a heating means for a vacuum deposition device using the vacuum deposition method, an electron beam heating method, a resistance heating method, or an induction heating method is preferable. In addition, the thickness of the metal layer is generally preferably in the range of 0.5 to 10 μm, and more preferably in the range of 1 to 8 μm. If the film thickness is in the above range or more, the flexibility of the deposited thin film is lost, and it becomes easier to suppress the occurrence of cracks, pinholes, etc. in the thin film due to external forces such as bending and pulling after film formation (in post-processing steps, etc.), which may deteriorate the electrode performance. On the other hand, if the film thickness is in the above range or less, the conductivity decreases, and the electrode characteristics (surface resistivity) may deteriorate.

[0016] The polyester constituting the polyester film of the present invention is a general term for a polymer having an ester bond as the main bonding chain of the main chain, and is preferably one having ethylene terephthalate and / or ethylene naphthalate units as the main constituent components from the viewpoints of heat resistance, film formability, etc. The definition of the main constituent components will be described later.

[0017] The polyester of the present invention may contain other copolymerization components within the range that does not impair the properties, and examples of the dicarboxylic acid components that can be used include aromatic dicarboxylic acids such as diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid, and isophthalic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, eicosanoic acid, adipic acid, sebacic acid, dimer acid, dodecanedioic acid, maleic acid, and fumaric acid, alicyclic dicarboxylic acids such as cyclohexynedicarboxylic acid, oxycarboxylic acids such as p-oxybenzoic acid, and polyfunctional acids such as trimellitic acid and pyromellitic acid. On the other hand, examples of the glycol components that can be used include aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, and triethylene glycol, alicyclic glycols such as cyclohexanedimethanol, aromatic glycols such as bisphenol A and bisphenol S, diethylene glycol, and polyalkylene glycol. Furthermore, polyethers such as polyethylene glycol, polytetramethylene glycol, etc. may be copolymerized. In the present invention, it is preferable that the polyester resin contains 70 mol % or more of an ethylene glycol component in 100 mol % of the diol component.

[0018] These dicarboxylic acid components and glycol components may be used in combination of two or more kinds, or two or more kinds of polyesters may be blended for use.Furthermore, two or more layers may be co-extruded to be used as a laminate film.

[0019] The polyester resin constituting the polyester film of the present invention is preferably one having ethylene terephthalate and / or ethylene naphthalate units as the main constituent component from the viewpoints of heat resistance and film formability, and more preferably one having ethylene terephthalate units as the main constituent component. Having ethylene terephthalate and / or ethylene naphthalate units as the main constituent component means that the polyester resin contains 70 mol % or more of an ethylene glycol component in 100 mol % of the diol component and contains 70 mol % or more of a terephthalic acid and / or a naphthalenedicarboxylic acid component in 100 mol % of the dicarboxylic acid component.

[0020] Furthermore, the polyester resin may contain polyethylene naphthalate, and in this case, it is preferable that the content is 0.5% by mass or more and 20% by mass or less from the viewpoint of heat resistance. More preferably, it is 1% by mass or more and 10% by mass or less. Even more preferably, it is 3% by mass or more and 5% by mass or less. If the content of polyethylene naphthalate is less than 0.5% by mass, the effect of improving heat resistance may not be effective. If the content of polyethylene naphthalate is more than 20% by mass, the compatibility of polyethylene terephthalate and polyethylene naphthalate is poor, it is difficult to form a crystal structure, and the orientation, heat resistance, and moist heat resistance may be reduced due to an increase in the amorphous structure. The biaxially oriented polyester film is preferably a biaxially oriented polyethylene terephthalate film / or a biaxially oriented polyethylene naphthalate film, and it is more preferable that the biaxially oriented polyester film is a biaxially oriented polyethylene terephthalate film. In addition, it is preferable that the melting point of the polyester is 250°C or more and 280°C or less. By setting the melting point to 250°C or more, durability against heat load during processing is good.

[0021] In addition, various additives, such as heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, and nucleating agents, may be blended into this polyester resin within the scope of not impairing the effects of the present invention.

[0022] The intrinsic viscosity (IV, unit: dl / g) of the polyester film is preferably 0.60 or more and 0.80 or less. When the thickness of the vapor-deposited film is 3 μm or more, it is more preferably 0.65 or more and 0.80 or less. When the IV is 0.60 or more, the molecular chain is sufficiently long, and the molecular mobility in a moist heat resistant environment is suppressed, thereby improving the heat resistance, and the end portion is reduced, thereby improving the hydrolysis resistance. Furthermore, the molecular chain is long, and even when the polyester film is heated to a high temperature during the thick film vapor deposition process, the molecular mobility is low, and the vapor-deposited film can be made uniform when the thick film is vapor-deposited, and the conductivity is improved and the electrode performance is stabilized. Furthermore, when the intrinsic viscosity is 0.80 or less, the viscosity does not become too high, and the breakage during film formation is reduced, improving productivity, and the thickness unevenness can be reduced. When the thickness unevenness is reduced, the vapor-deposited film can be made uniform when the thick film is vapor-deposited, and the conductivity is improved and the electrode performance is stabilized. The method for adjusting the IV is not particularly limited, but includes a method of performing melt polymerization or solid-phase polymerization in a batch or continuous manner at the stage of polyester raw materials, similar to the case of commonly used polyesters. The solid-phase polymerization method is more preferable because the polymerization time is relatively short and the carboxyl end group concentration can be reduced with an increase in viscosity, and adjustment is possible by the solid-phase polymerization time and the amount of catalyst added. In addition, when the polyester raw materials are melt-formed into a polyester film, hydrolysis and thermal decomposition due to the moisture remaining in the molten state progress, so it is preferable that the IV of the polyester raw materials before melt extrusion used as the raw materials for the film is higher than the target value of the IV of the polyester resin constituting the film. Therefore, even if the IV of the polyester resin of the raw materials for the film is higher than the target value of the IV of the polyester resin constituting the film, it is preferable that the difference is small, and the IV of the polyester resin of the raw materials for the film is preferably 0.05 to 0.15 higher than the target value of the IV of the polyester resin constituting the film. In addition, the IV is determined by the method described in the examples.

[0023] The degree of crystallinity of the polyester film of the present invention as determined by differential scanning calorimetry is preferably 30.0 to 50.0%, more preferably 35.0 to 50.0%, and further preferably 40.0 to 50.0%. The degree of crystallinity is determined by the following method. <Measurement method> Measure by heating from 25°C to 300°C at a heating rate of 20°C / min. The degree of crystallinity (Χc) is calculated from the differential scanning calorimetry chart obtained using the heat of crystalline fusion (ΔHm) and the heat of cold crystallization (ΔHc) according to the following formula. Χc=(ΔHm-ΔHc) / ΔHm0 Here, ΔHm0 is 140.10 J / g, which is the heat of fusion of perfectly crystalline PET.

[0024] By setting the crystallinity at 30.0% or more, the heat resistance and dimensional stability are improved, and the deposited film can be made uniform by regularly arranging the deposited metal during thick-film deposition, which tends to cause the film to reach high temperatures, and the surface resistivity can be improved. Furthermore, by setting the crystallinity at 50.0% or less, embrittlement of the film surface can be suppressed, and defects in the deposited film can be suppressed in the transport system after deposition, which can prevent the surface resistivity from decreasing. Methods for adjusting the crystallinity include a method of adding a crystal nucleating agent and a method of adjusting the conditions of the stretching process and the heat treatment process, and from the perspective of cost, a method of adjusting the crystallinity at the stretching process and the heat treatment process is preferable. Furthermore, adjustment at the heat treatment process is preferable, as it is easier to control the melting subpeak described below. When adjusting at the stretching process and the heat treatment process, it is important to balance the strength and the heat shrinkage rate.

[0025] The polyester constituting the polyester film of the present invention preferably has a diethylene glycol (DEG) content of 1.5% by mass or less in the polyester film. More preferably, it is 1.2% by mass or less, and even more preferably, it is 1.0% by mass or less. The present inventors have found that parts of the polyester film with a large amount of DEG tend to become random amorphous parts, and molecular chains are more likely to move when heated than crystalline parts or oriented amorphous parts, and have found that by setting the DEG content to 1.5% by mass or less, even if the polyester film becomes hot during thick-film deposition, the molecular chains are less likely to move due to the small number of random amorphous parts, and the heat resistance is improved and flatness is maintained. By setting the IV and crystallinity within the above-mentioned ranges and the DEG content in the film within the above-mentioned ranges, the evaporated metal atoms on the flat film surface during thick-film deposition are regularly arranged, and the evaporated film becomes uniform due to the small number of missing parts, and the electrode performance can be stabilized. Furthermore, the heat history that the polyester film receives in the vapor deposition process reduces the heat resistance of the film, which can cause the film to stretch in response to external forces in subsequent processing steps, resulting in wrinkles, unstable running properties of the film, and poor processability. It is also possible to prevent defects from occurring in the vapor deposition film and a decrease in surface resistivity.

[0026] The amount of DEG can be reduced by, but is not limited to, shortening the polymerization time, limiting the amount of antimony compounds, germanium compounds, titanium compounds, etc. used as polymerization catalysts, combining liquid-phase polymerization with solid-phase polymerization, or adding an alkaline component. For example, when potassium hydroxide is added as an alkaline component to adjust the amount of DEG, a polyester resin having a DEG amount of 0.01% by mass or more and 1.5% by mass or less can be obtained by adding 0.01 parts by mass or more and 0.10 parts by mass or less of potassium hydroxide per 100 parts by mass of dimethyl terephthalate. The amount of DEG in the film is determined by the method described in the examples.

[0027] Representative examples of particles that can be contained in the polyester film of the present invention include inorganic particles such as particles, aggregates, silicon dioxide particles, calcium carbonate particles, alumina particles, titanium oxide particles, barium sulfate particles, aluminum silicate particles, calcium phosphate particles, mica, kaolin, clay, etc., which are produced by various nucleating agents during polymerization, and organic particles such as crosslinked polystyrene particles, acrylic particles, imide particles, silicone particles, etc., or mixtures thereof. Among these, inorganic particles such as silicon dioxide particles, calcium carbonate particles, alumina particles, aluminum silicate particles, etc., or mixtures of these inorganic particles with particles produced by various nucleating agents during polymerization are preferred.

[0028] The diameter of the various particles used is not particularly limited, but the average particle diameter measured by a sedimentation method or a light scattering method is preferably 0.05 to 8.0 μm, more preferably 0.1 to 4.0 μm. The content of such particles is preferably 0.01 to 0.2 mass % of the entire film, more preferably 0.02 to 0.15 mass %.

[0029] The polyester constituting the polyester film of the present invention preferably has a carboxyl end group amount of 25 to 55 equivalents / ton, more preferably 35 to 50 equivalents / ton. By making the carboxyl end group amount 25 equivalents / ton or more, the adhesion between the polyester film and the vapor-deposited film during vapor deposition is improved. In addition, by making the carboxyl end group amount 55 equivalents / ton or less, problems such as coloration of the polyester film and deterioration of the film formability of the polyester film can be suppressed.

[0030] The polyester film of the present invention preferably has a thickness of 1.5 to 15 μm. By making the thickness 1.5 μm or more, even when a minute foreign object enters the battery, there is partial stress concentration, and the battery operating temperature is high, the electrode film is less likely to be punctured (i.e., the temperature at which the electrode film begins to be punctured becomes high), and the efficiency decrease due to the deformation of the electrode can be suppressed even at high operating temperatures. From the same viewpoint, it is more preferable that the thickness is 3.0 μm or more, and even more preferable that the thickness is 5.0 μm or more. In addition, by making the thickness 15 μm or less, the weight of the electrode can be reduced, which can contribute to improving the energy density of the battery. From the same viewpoint, it is more preferable that the thickness is 13 μm or less, more preferably 6.9 μm or less, and particularly preferably less than 6.5 μm. The thickness is determined by the method described in the examples.

[0031] The substrate film used in the present invention may have a single layer structure, or a laminate structure composed of resin compositions A, B, and C having different compositions, such as a two-layer structure of A / B, a three-layer structure of A / B / A or A / B / C, or a laminate structure having more than three layers. The laminate thickness ratio in this case may also be set arbitrarily. These laminate structures can be produced as laminate films by coextrusion.

[0032] The polyester film of the present invention preferably has a center surface average roughness (SRa) of 40 to 100 nm on both sides. More preferably, it is 50 to 100 nm. The center surface average roughness SRa is a parameter of three-dimensional surface roughness obtained by a measurement method described later. By setting the SRa within the above-mentioned range, the adhesive surface area with the vapor-deposited film during vapor deposition processing is increased, and sufficient adhesiveness as an electrode can be obtained. Furthermore, the slipperiness is also good, which makes it easy to wind up in the processing step and suppresses the occurrence of blocking. On the other hand, if the SRa is less than 40 nm, the adhesive surface area with the vapor-deposited film is reduced, and sufficient adhesiveness as an electrode may not be obtained. Also, if it exceeds 100 nm, the protrusions may damage the vapor-deposited film during winding in vapor deposition processing, thereby reducing the electrode performance.

[0033] The polyester film of the present invention preferably has a strength of 110 MPa or more when elongated by 5% in the longitudinal direction. More preferably, it is 120 MPa or more. If the strength of the polyester film at 5% elongation in the longitudinal direction is less than 110 MPa, the film may be wrinkled due to the process tension during the transport process after deposition in the deposition process, or the substrate film may be stretched, which may cause the deposition film to easily break or crack, thereby deteriorating the electrode performance. The strength at 5% elongation in the longitudinal direction is determined by the method described in the Examples.

[0034] The method for setting the breaking strength and the strength at 5% elongation within the above-mentioned range is not particularly limited, but examples include a method of adjusting the stretching temperature and stretch ratio in the longitudinal stretching process. In this case, if the film ends are heated using an infrared heater for end heating, the longitudinal stretching process is stabilized and becomes easier to control. At this time, since each strength is affected by the stretching temperature, stretch ratio, and temperature and time of the heat setting treatment in the transverse stretching process, it is preferable to balance each strength so that it falls within the range.

[0035] The polyester film of the present invention has a heat shrinkage rate after heating at 190°C for 20 minutes of preferably 3 to 8% in the longitudinal direction and the width direction. More preferably, it is 4 to 7%. By setting the heat shrinkage rate within the above range, when an electrode is short-circuited due to a conductive needle-like object, such as a nail, being pierced in a lithium ion secondary battery, heat is generated due to the short circuit once, but the damaged part (hole) of the film instantly expands due to heat shrinkage, and at this time, the vapor deposition film also becomes a hole together with the film, so that the short circuit can be prevented from continuing. If it is less than 3%, the heat shrinkage is insufficient, so that the damaged part (hole) of the film is small and it may not be possible to prevent the short circuit from continuing. On the other hand, if it exceeds 8%, the damaged part (hole) of the film may become large, causing defects such as leakage of electrolyte, or the film itself may be deformed significantly, causing the electrode to be short-circuited by the vapor deposition film itself.

[0036] Furthermore, the polyester film of the present invention preferably has a heat shrinkage rate of 1.0% or more in both the longitudinal and transverse directions after heating at 190°C for 20 minutes. More preferably, it is 1.5% or more. When the heat shrinkage rate is within the above-mentioned range, the shape of the broken part (hole) is well balanced, and the continuation of short circuit can be prevented. When it is less than 1%, the shape of the broken part (hole) may be biased, or the area of ​​the hole may be too small to prevent the continuation of short circuit of the electrode, and further, the shrinkage speed may be slowed, and the prevention of short circuit may be delayed. There is no particular limitation on the method for making the heat shrinkage rate in the longitudinal and transverse directions after heating at 190°C for 20 minutes within the above-mentioned range, but examples of the method include a method of controlling the stretching temperature and stretch ratio in the longitudinal stretching process, the stretching temperature and stretch ratio in the transverse stretching process, and the temperature and time in the heat setting process, a method of performing a tension heat treatment or a relaxation heat treatment in the heat setting process, and a method of performing a relaxation treatment at a low temperature (for example, 190°C) after the heat setting process. The thermal shrinkage rate after heating at 190° C. for 20 minutes is determined by the method described in the examples.

[0037] The polyester film of the present invention preferably has a planar orientation coefficient (fn) of 0.155 to 0.168. More preferably, it is 0.158 to 0.165. Within the above range, the orientation of the film is good, and the film is less likely to lose strength or stretch due to external forces, and has good suitability for deposition processing. In addition, the film has good adhesion to the deposited film, and peeling and falling off of the deposited film can be suppressed in the processing step after deposition. If the planar orientation coefficient (fn) is less than 0.155, problems such as wrinkles are likely to occur during processing, and if it exceeds 0.168, the deposited film is likely to peel off due to cleavage of the film, etc., and problems during processing may be likely to occur.

[0038] The polyester film of the present invention preferably has an average crystal grain size (χc) of 5.0 to 8.0 nm, more preferably 5.3 to 6.8 nm. When χc is 5.0 or more, the deposited film becomes uniform when deposited, and the adhesion between the film and the deposited film becomes good, thereby improving the electrode performance. From the viewpoint of productivity and film strength, χc is preferably 8.0 nm or less, but if it exceeds 6.8 nm, the film may become brittle and the puncture strength may decrease. The method of controlling χc is not particularly limited, but a method of controlling the crystallization of the polyester resin by heat setting conditions, etc., can be mentioned. For example, if the heat setting temperature after stretching is increased or the heat setting time is extended, the crystallization of the polyester resin can be promoted, so that χc tends to increase. On the other hand, if the heat setting temperature is too high or the heat setting temperature is too long, the crystallized material melts, so that χc tends to decrease. A film having a desired χc value can be obtained by appropriately adjusting the heat setting temperature and time according to the polyester resin constituting the polyester film. It should be noted that χc is determined by the method described in the examples.

[0039] The polyester film of the present invention preferably has a micro endothermic peak temperature (Tmeta) of 220°C or higher. More preferably, it is 225°C or higher, and even more preferably, it is 230°C or higher. When Tmeta is 220°C or higher, the thermal crystallization of the polyester film proceeds sufficiently, and the crystallinity is easily adjusted to the above-mentioned range. Therefore, when vapor-deposited, the vapor-deposited film becomes uniform, and the electrode performance can be improved. Furthermore, the thermal dimensional stability at high temperatures can be improved, and the film is less likely to stretch due to the heat of the vapor-deposited metal during vapor-deposition processing, and the uniformity of the vapor-deposited film can be maintained.

[0040] The minute endothermic peak temperature of the film is obtained by the following measurement. The film is measured with a differential scanning calorimeter (DSC Q100 manufactured by TA Instruments) at a heating rate of 20°C / min to determine the melting peak temperature (melting point), and the minute endothermic peak temperature generated by the transformation of the pseudocrystal during this measurement is defined as Tmeta. Note that Tmeta appears as the history of the heat treatment temperature for the polyester film.

[0041] A preferred embodiment of the method for producing a biaxially oriented polyester film for thick deposition according to the present invention will be specifically described below, although the present invention is not limited to the following method.

[0042] The biaxially oriented polyester film for thick deposition of the present invention may have a structure as a coextruded laminate film of two or more layers.

[0043] The polyester resin used in the polyester film of the present invention preferably has a melting point of 250° C. or higher in terms of heat resistance and film-forming properties. Commercially available polyester resins can be used as they are, but they may also be produced through a polycondensation reaction as described below and used.

[0044] 0.09 parts by mass of magnesium acetate and 0.03 parts by mass of antimony trioxide are added to a mixture of 100 parts by mass of dimethyl terephthalate and 70 parts by mass of ethylene glycol, and the mixture is gradually heated, and finally, at 220°C, an ester exchange reaction is carried out while distilling off methanol, to synthesize a precursor of polyethylene terephthalate. Next, 0.02 parts by mass of an 85% aqueous solution of phosphoric acid (molar concentration 14.6 mol / L) is added to the precursor, and the mixture is transferred to a polycondensation reaction vessel. The reaction system is gradually depressurized while heating and increasing the temperature in the polycondensation reaction vessel, and a polycondensation reaction is carried out at 290°C under a reduced pressure of 1 hPa, to obtain a polyester resin having a desired molecular weight. When particles are added, it is preferable to add a slurry in which particles are dispersed in ethylene glycol to the polycondensation reaction vessel so as to obtain a predetermined particle concentration, and then carry out the polycondensation reaction. The intrinsic viscosity and the amount of DEG are adjusted by the above-mentioned method.

[0045] Next, a preferred method for producing the polyester film of the present invention using the polyester resin will be specifically described. First, the polyester resin to be used is heated under reduced pressure or in a nitrogen atmosphere, and dried, for example, at 150° C. for 5 hours, preferably to reduce the moisture content in the resin to 50 ppm or less.

[0046] Then, the resin is fed to an extruder to perform melt extrusion. When a vent-type twin-screw extruder is used, the drying step may be omitted. When a plurality of polyester resins are mixed and used, they may be mixed in a drying step to a predetermined mixing ratio, or the mixing ratio may be measured when feeding the resin to the extruder. The resin thus melt-extruded is filtered to remove foreign matter while in the molten state, the extrusion amount is measured by a gear pump, and the resin is extruded as a molten sheet from a T-die having a slit-shaped discharge port, and is solidified by adhering to a cooling roll to obtain a cast film (unoriented film (unstretched film)). In order to improve the adhesion between the molten sheet and the cooling roll, it is usually preferable to adopt an electrostatic application adhesion method and / or a liquid surface application adhesion method.

[0047] The cast film is biaxially stretched. First, the film is heated by a group of rolls heated to a temperature higher than the glass transition temperature of the polyester resin, for example, 90°C to 135°C, more preferably 100°C to 130°C, by heating the film with two or more infrared heaters for full width heating and end heating, and stretched 4.0 to 5.5 times in the film longitudinal direction (MD) to obtain a uniaxially oriented film (uniaxially stretched film). Next, the film is stretched 3.5 to 5.0 times in the film transverse direction (TD), preferably at a temperature higher than 100°C and lower than 130°C.

[0048] The film thus obtained is preferably subsequently heat-set in-line and / or off-line. Furthermore, if necessary, it may be stretched again in MD and / or TD before or after heat-setting. The heat-setting temperature is preferably 220 to 245°C, which can prevent heat damage due to the heat of deposition by promoting crystallization of the film surface on the deposition side, and can improve the electrode characteristics (surface resistivity) by homogenizing the deposition film (orderly arranging metal particles). Therefore, it is more preferable to set it to 225 to 245°C, and particularly preferable to set it to 230 to 245°C. The heat treatment time is usually 1 second to 1 minute. In addition, in this heat-setting process, the heat shrinkage characteristics can be adjusted by performing a relaxation treatment in the longitudinal direction and / or the transverse direction.

[0049] After the heat setting treatment, a polyester film with complete crystal orientation can be obtained by passing through a cooling zone at 100 to 200° C. For example, after heat setting, the film can be rapidly or slowly cooled, or an intermediate cooling zone can be provided to adjust the heat shrinkage stress.

[0050] The film may be coated as necessary. By providing a coating layer on the film, the adhesion to the deposition layer and the conductive ink layer in particular can be improved. The coating liquid is dissolved in water, emulsified or suspended in consideration of explosion-proofing and environmental pollution. The coating layer may be applied to a biaxially stretched film after completion of crystal orientation or to a film before completion of crystal orientation and then stretched. The latter method is particularly preferred in order to more significantly exhibit the effects of the present invention. The method of application is not particularly limited, but it is preferable to apply the coating using a roll coater, gravure coater, reverse coater, kiss coater, bar coater, etc. In addition, the surface to be coated may be subjected to corona discharge treatment in air or other various atmospheres before coating, as necessary.

[0051] The coating layer may contain, as necessary, an antifoaming agent, a coating crosslinking agent, a thickener, an organic lubricant, inorganic particles, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

[0052] A preferred embodiment of the battery of the present invention is a battery having the biaxially oriented polyester film for thick deposition described above. This embodiment reduces pinholes and allows the battery to withstand processing tension, and improves the resistance characteristics of the electrode sheet, leading to improved battery performance such as high output and long life. EXAMPLES

[0053] [Method of measuring characteristic values] (1) Thickness Ten stacked test pieces were measured using a micrometer in accordance with JIS C2151 (2019). The thickness measurement was divided by 10 to obtain the thickness at each measurement point, and the average value was obtained.

[0054] (2) Intrinsic viscosity (IV) The polyester resin or polyester film was dissolved in 100 mL of orthochlorophenol (solution concentration C = 1.2 g / mL), and 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 according to the following formula (C), and the obtained value was taken as the intrinsic viscosity (IV). ηsp / C=[η]+K[η]2·C····Formula (C) (Here, ηsp = (solution viscosity / solvent viscosity)-1, and K is the Huggins constant (assumed to be 0.343).)

[0055] In addition, when the solution in which the polyester resin or polyester film was dissolved contained insoluble matter such as inorganic particles, the solution was filtered and the mass was measured, and a correction was performed in which the mass of the filtered matter was subtracted from the mass of the measured sample to obtain the measured sample mass.

[0056] (3) Micro endothermic peak temperature (Tmeta) The film is measured with a differential scanning calorimeter (DSC Q100 manufactured by TA Instruments) at a heating rate of 20°C / min to determine the melting peak temperature (melting point), and the minute endothermic peak temperature generated by the transformation of the pseudocrystal during this measurement is defined as Tmeta. Note that Tmeta appears as the history of the heat treatment temperature for the polyester film.

[0057] (4) Diethylene glycol (DEG) content 1.0 g of the measurement sample (polyester resin or polyester film) was decomposed at 260 ° C. using 2.5 mL of monoethanolamine containing 0.4 mass % of 1,6-hexanediol. Then, 10 mL of methanol was added and cooled, neutralized with terephthalic acid, centrifuged, and the supernatant was measured for diethylene glycol (DEG) content by gas chromatography (Shimadzu Corporation GC-14A). Since additive components such as inorganic particles settle as insoluble matter during centrifugation, the sedimented components were filtered and mass measured, and the mass was subtracted from the measurement sample mass to correct the measurement sample mass. For example, if 1.0 g of the measurement sample was hydrolyzed and the DEG content was detected to be 0.0020 g by gas chromatography, the DEG content was 0.20 mass %.

[0058] (5) Crystallinity 5 mg of film samples were weighed into a sample pan and measured using a differential scanning calorimeter (TA Instruments DSC Q100) by heating from 25°C to 300°C at a heating rate of 20°C / min. The crystallinity (Χc) was calculated from the differential scanning calorimeter chart obtained using the heat of fusion (ΔHm) and the heat of cold crystallization (ΔHc) according to the following formula. Χc=(ΔHm-ΔHc) / ΔHm0 Here, ΔHm0 was used as the heat of fusion of perfectly crystalline PET, 140.10 J / g.

[0059] (6)Surface resistivity The deposited film was left in an environment of 25°C and 65% relative humidity for 24 hours, and then measurements were taken in that atmosphere after applying a voltage of 100 V for 10 seconds using a digital ultra-high resistance / microammeter R8340A (manufactured by Advantest Corporation).

[0060] (7) Average grain size (χc) The diffraction intensity of the sample was measured using a PHILIPS Compact X-ray Diffractrometer System PW1840 with Cu Kα radiation (wavelength 0.1542 nm) as a light source under the following conditions. Scanning range: 18~32° Scanning speed: 0.05° / sec Accelerating voltage: 35 kV Bulb current 15mA The average crystal grain size (χc) is calculated from the half-width (rad) of the maximum peak. χc=0.9λ / βcosθ Calculation was performed using λ: X-ray wavelength (nm), β: half-width of maximum peak (rad), and θ: diffraction angle of maximum peak.

[0061] (8) Adhesion of evaporated film An adhesive prepared by mixing Toyo Morton's "Adcoat" (registered trademark) 503 (AD503), hardener CAT-10, and ethyl acetate in a ratio of 100:5:100 mass% was applied to the deposition surface of the sample using a #12 Mayer bar. After application, the adhesive was dried for 30 seconds in a hot air oven at 70°C, and then laminated to the corona-treated surface of a 60 μm-thick unstretched polypropylene film, and aged for 72 hours at 40°C using a hot air oven. The laminated sample was cut to a width of 15 mm, and the peel force between the polypropylene film and polyester film was measured at a peel angle of 90° using Orientec's "TENSILON" (registered trademark) UCT-100 under an atmosphere of room temperature of 23°C and relative humidity of 65%. A:400g / 15mm width or more B: 200g / 15mm width or more, 400g / 15mm width or less C: Less than 200g / 15mm width.

[0062] Next, the polyester film of the present invention will be specifically described with reference to examples. In the examples, "parts" refers to "parts by mass" unless otherwise noted.

[0063] [Production of polyethylene terephthalate] The polyethylene terephthalate resin was prepared as follows.

[0064] (1) Polyethylene terephthalate resin (PET-1) To a mixture of 100 parts by mass of dimethyl terephthalate and 61 parts by mass of ethylene glycol, 0.04 parts by mass of magnesium acetate and 0.02 parts by mass of antimony trioxide were added, and the temperature was gradually raised, and finally, an ester exchange reaction was carried out while distilling off methanol at 220°C. Next, 0.020 parts by mass of an 85% aqueous solution of phosphoric acid was added to the ester exchange reaction product, and then the mixture was transferred to a polycondensation reaction vessel. Furthermore, the reaction system was gradually depressurized while heating and raising the temperature, and a polycondensation reaction was carried out by a conventional method at 290°C under a reduced pressure of 1 hPa to produce a polyethylene terephthalate resin (hereinafter, "PET-1").

[0065] (2) Isophthalic acid copolymerized polyethylene terephthalate resin (PET-2) Dimethyl terephthalic acid was used in an amount of 150.4 parts by mass, and dimethyl isophthalic acid was used in an amount of 43.6 parts by mass (M=22.5). Polymerization was carried out in the same manner as for PET-1, and polymerization time was adjusted to prepare an isophthalic acid-copolymerized polyethylene terephthalate resin (PET-2).

[0066] (3) Particle Master When producing the polyethylene terephthalate (1) above, after the transesterification reaction, an ethylene glycol slurry of aggregated silica particles having a median diameter (average particle diameter) of 2.1 μm as measured by a laser diffraction / scattering particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.) was added, and then a polycondensation reaction was carried out to obtain a particle master (hereinafter referred to as "PET-3") having a particle concentration of 2.0 mass%.

[0067] The amount of diethylene glycol was adjusted by the amount of potassium hydroxide added, and the intrinsic viscosity was adjusted by the polymerization time by the solid-phase polymerization method. The amount of diethylene glycol and the intrinsic viscosity in the table are values ​​measured in the film state.

[0068] Example 1 PET-1 was mixed at a ratio of 90 parts by mass and 10 parts by mass of PET-3. The mixture of PET-1 and PET-3 was vacuum dried, then fed to an extruder, melt-extruded at 280°C, filtered through a 14μm cut stainless powder sintered filter (PSS), extruded into a sheet from a T-shaped die, and cooled and solidified by electrostatic adhesion onto a cooling drum with a surface temperature of 25°C. The unstretched (unoriented) PET film thus obtained was heated to 127°C and stretched in three stages in the longitudinal direction at 2.21 times in the first stage, 1.14 times in the second stage, and 2.30 times in the third stage to form a uniaxially stretched film. This film was stretched 3.8 times in the width direction while being heated to 112°C (transverse stretching). The film was introduced into hot air at 227°C and heat-treated (heat-set) for 3 seconds without relaxation in the MD and TD directions, then relaxed (relaxed) at 150°C in the width direction by 3.0% relative to the film width after TD stretching, and then cooled. In this way, a polyester film with a thickness of 5.7 μm was finally obtained.

[0069] Aluminum was vapor-deposited at a predetermined vapor deposition rate on the polyester film thus obtained with a thickness of 5.7 μm. The method of vapor-depositing aluminum was to set the film on the unwinding device of a continuous vacuum vapor-depositing machine, run it over a cooled metal drum, and wind the film. At this time, the continuous vacuum vapor-depositing machine was turned on for 10 -4 The pressure was reduced to below Torr, 99.99% pure aluminum metal was loaded into an alumina crucible from the bottom of the cooling drum, and the aluminum metal was heated and evaporated, deposited on the film, and a 1 μm thick aluminum film was formed. This process was repeated three times. The opposite side was also vapor-deposited three times in the same way, forming a 3 μm thick aluminum vapor-deposited film on both sides, resulting in a vapor-deposited film with a total thickness of 11.7 μm.

[0070] The intrinsic viscosity and diethylene glycol amount (DEG amount) in the table are values ​​in the film state (before deposition). In order to approach these values, the intrinsic viscosity was adjusted by changing the polymerization time using the solid-state polymerization method, and the diethylene glycol amount was adjusted by changing the amount of potassium hydroxide added.

[0071] (Examples 2 to 8, Comparative Examples 2 to 3) The film-forming conditions (stretching conditions, heat setting conditions, and cooling conditions) were changed, and a polyester film and an aluminum-deposited film were obtained in the same manner as in Example 1. The results are shown in Table 1.

[0072] Comparative Example 1 PET-2 was mixed at a ratio of 80 parts by mass and 20 parts by mass of PET-3. The mixture of PET-2 and PET-3 was vacuum dried, then fed to an extruder, melt-extruded at 270°C, filtered through a 14μm cut stainless powder sintered filter (PSS), extruded into a sheet from a T-shaped die, and cooled and solidified by electrostatic adhesion onto a cooling drum with a surface temperature of 25°C. The unstretched (unoriented) PET film thus obtained was heated to 110°C and stretched in three stages in the longitudinal direction at 2.20 times the first stage, 1.10 times the second stage, and 1.50 times the third stage to form a uniaxially stretched film. This film was stretched 3.6 times in the width direction while being heated to 110°C (transverse stretching). This film was introduced into hot air at 125°C and heat-treated (heat-set) for 2 seconds without relaxation in the MD and TD directions, and then cooled at 105°C without relaxation in the TD direction. In this manner, a polyester film copolymerized with isophthalic acid having a thickness of 12.0 μm was finally obtained.

[0073] The deposited films using the polyester films obtained in the Examples as substrates were excellent in adhesion to the deposited film and surface resistivity, whereas the aluminum deposited films using the polyester films obtained in the Comparative Examples 1 to 3 as substrates were inferior.

[0074] [Table 1] [Industrial Applicability]

[0075] According to the present invention, it is possible to provide a biaxially oriented polyester film for thick deposition in which the resistance characteristics of the electrode sheet are improved, which leads to improved battery performance such as high output and long life. The film can be suitably used particularly as an electrode film for batteries.

Claims

1. A biaxially oriented polyester film for thick deposition that satisfies the following (1) to (3): (1) The degree of crystallinity determined by differential scanning calorimetry using the following method is 30.0 to 50.0%. <Measurement method> The sample is heated from 25°C to 300°C at a temperature increase rate of 20°C / min and measured. The crystallinity (Xc) is calculated from the differential scanning calorimetry chart obtained using the heat of crystalline fusion (ΔHm) and the heat of cold crystallization (ΔHc) according to the following formula: Χc=(ΔHm−ΔHc) / ΔHm0 Here, ΔHm0 is 140.10 J / g, which is the value of the heat of fusion of perfectly crystalline PET. (2) Intrinsic viscosity (IV, unit: dl / g) of 0.60 to 0.

80. (3) The amount of DEG (diethylene glycol) in the polyester film, as determined by the following method, is 1.5% by mass or less. <Measurement Method> 1.0 g of polyester film was decomposed at 260°C using 2.5 mL of monoethanolamine containing 0.4% by mass of 1,6-hexanediol. 10 mL of methanol was then added, the mixture was cooled, neutralized with terephthalic acid, and centrifuged. The supernatant was then subjected to gas chromatography to measure the diethylene glycol (DEG) content. Since added components such as inorganic particles settle as insoluble matter during centrifugation, the sedimented components were filtered and weighed, and this mass was subtracted from the measured sample mass to correct for the measured sample mass.

2. 2. The biaxially oriented polyester film for thick deposition according to claim 1, wherein the minute endothermic peak temperature (Tmeta) is 220°C or higher.

3. 3. The biaxially oriented polyester film for thick deposition according to claim 1, wherein the thickness of the biaxially oriented polyester film is 1.5 to 15 μm.

4. 3. A battery electrode film using the biaxially oriented polyester film for thick vapor deposition according to claim 1 or 2.

5. The electrode film for a secondary battery according to claim 4 .

6. The electrode film for a lithium ion secondary battery according to claim 5 .

7. A battery comprising the electrode film of claim 4.