JP2011174009A - Flame-retardant polyester film for electric storage element electrode, electrode for electric storage element comprising the same, and electric storage element comprising the same - Google Patents

Abstract

A power storage element having high piercing resistance, bending resistance and flame resistance suitable for a power storage element electrode application while being a thin polyester film capable of higher volume and weight energy density than conventional products. A flame-retardant polyester film for electrodes is provided.
A flame-retardant polyester film having at least one polyester layer A mainly composed of polyethylene naphthalene dicarboxylate, wherein the polyester layer A is at least one of a carboxyphosphinic acid compound and a carboxyphosphinic acid compound. Is equivalent to a diffraction peak having a Bragg angle of 25 ° to 29 ° obtained by wide-angle X-ray diffraction measurement in the polyester film. A flame-retardant polyester film for a storage element electrode, wherein the degree of coincidence of the crystal plane normal to the film plane normal is 0.95 or more and the film thickness is 0.2 μm or more and 30 μm or less.
[Selection figure] None

Description

  The present invention relates to a flame retardant polyester film for an electricity storage element electrode, an electrode for an electricity storage element comprising the same, and an electricity storage element comprising the same. More specifically, a flame retardant polyester film for a storage element electrode that uses a polyester film as a base material instead of a conventional metal electrode and has excellent safety such as ignition due to a short circuit, an electrode for a storage element comprising the same, and It is related with the electrical storage element which becomes.

In recent years, the use of local electrical energy has increased due to the generation of natural energy such as sunlight and wind power, the spread of next-generation vehicles such as HV, EV, and FCV, and the spread of portable electronic devices. Along with this, the need for power storage systems is increasing.
Specifically, input and output, such as temporarily storing power supplied from fluctuating natural energy according to consumption, or assisting power supply to follow a power supply source such as a fuel cell to fluctuate power consumption. There is an increasing need for a power storage system that can follow the large fluctuations of the power storage system and a power storage system that can carry a large amount of stored power in order to enhance the convenience of local use.

The main components of such a power storage system are power storage elements such as secondary batteries and capacitors, and in particular, lithium ion secondary batteries, electric double layer capacitors, lithium ion capacitors, etc. will be promising in the future. .
These energy storage devices store and release (charge / discharge) electrical energy through the oxidation / reduction reactions of ions on the positive and negative electrode surfaces and the generation of electric double layers (charge / discharge). A function as a current collector for taking out is necessary, and a metal foil having a thickness of about 10 to 30 μm is conventionally used as a base material for an electrode.

In order to meet the demand for larger capacity and smaller size required for power storage systems in recent years, the electrode substrate has been made thinner for the purpose of improving volumetric energy density and weight energy density to meet the demand for portability. Is underway. However, there is a limit to thinning the film while maintaining characteristics such as piercing resistance so that the electrode does not penetrate through conduction due to process handling of the electrode, bending resistance, and nail.
Therefore, as a new material to replace metal, the present inventor has a current collector function of a material having a structure in which a metal thin film layer is provided on the surface of a biaxially stretched polyester thin film excellent in mechanical properties and heat-resistant dimensional stability. (Patent Documents 1 and 2), however, have not yet been fully examined for various characteristics at a practical level in place of metal plates.

  Further, in the next generation power storage system with extremely high energy density, there is a concern about the risk of ignition in the event of a short circuit, and the components used in the next generation power storage system are required to be flame retardant. Even when a polyester film is used as an electrode base material layer, high flame retardancy is required, but polyester itself is not a flame retardant material. In recent years, various studies have been made to impart flame retardancy to a polyester film using a flame retardant containing no halogen, but it has been pointed out that it is difficult to achieve both flame retardancy and other properties. Among them, it has been proposed to use a carboxyphosphinic acid compound for a polyethylene naphthalate film as a flame retardant capable of achieving both flame retardancy and mechanical properties (Patent Document 3). However, the film disclosed in Patent Document 3 still does not have sufficient characteristics required as an electrode base material for a power storage element, such as puncture resistance.

Furthermore, in order to increase the volume / weight energy density of the electricity storage element compared to conventional products using a polyester film as an electrode base material having a current collector function, although the effect is higher as the film thickness is thinner, it is thinner. Therefore, the puncture resistance and the bending resistance are likely to be lowered.
As described above, a polyester film having a specific gravity smaller than that of the metal foil is used as the electrode base material of the electricity storage element instead of the metal foil, and the volume and weight energy density is higher than that of the conventional product when the thickness is reduced. In addition, there is a need for a film for a storage element electrode that can prevent a short circuit due to conduction due to excellent puncture resistance and bending resistance, and has a flame retardant function in the event of ignition due to a short circuit. .

Japanese Patent Laid-Open No. 10-40919 Japanese Patent Laid-Open No. 10-40920 Japanese Patent Laid-Open No. 2007-9111

  The object of the present invention is to eliminate the problems of the prior art and to provide a high puncture resistance suitable for use as a storage element electrode while being a thin polyester film capable of higher volume and weight energy density than conventional products. It is providing the flame retardant polyester film for electrical storage element electrodes which has a property, a bending resistance, and a flame retardance.

  As a result of intensive studies to solve the above problems, the present inventors have added at least one of a carboxyphosphinic acid compound or a carboxyphosphinic acid compound as a phosphorus flame retardant to a polyethylene naphthalene dicarboxylate base film. In this case, flame retardancy can be imparted without hindering the high bending resistance of the polyester film, and at the same time, by arranging the naphthalene ring parallel to the film surface to be extremely high, It has been found that the high puncture resistance required for an electrode substrate film can be obtained, and as a result, it is possible to reduce the thickness of the electrode substrate electrode, and the present invention has been completed.

  That is, an object of the present invention is a flame retardant polyester film having at least one polyester layer A mainly composed of polyethylene naphthalene dicarboxylate, and the polyester layer A is at least one of a carboxyphosphinic acid compound and a carboxyphosphinic acid compound. Or a component derived from one kind as a phosphorus atom with respect to the polyester layer A in the range of 0.01% by weight to 3% by weight, and a Bragg angle obtained by wide-angle X-ray diffraction measurement in the polyester film of 25 ° Achieved by a flame-retardant polyester film for a storage element electrode having a degree of coincidence of a crystal plane normal corresponding to a diffraction peak of 29 ° with a film plane normal of 0.95 or more and a film thickness of 0.2 μm or more and 30 μm or less. The

（式中、Ｒ^１は炭素数１〜１０のアルキル基または炭素数６〜１８のアリール基、Ｒ^２およびＲ^３は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^１〜Ｒ^３はそれぞれ同一でも異なっていてもよい）
該カルボキシ亜ホスフィン酸化合物が下記式（II）で表わされる化合物であること、

（式中、Ｒ^４は炭素数１〜１０のアルキル基または炭素数６〜１８のアリール基、Ｒ^５およびＲ^６は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^４〜Ｒ^６はそれぞれ同一でも異なっていてもよい）
該難燃ポリエステルフィルムが該ポリエステル層Ａの少なくとも片面にさらにポリエステル層Ｂが積層された積層構成であり、該ポリエステル層Ｂの主たる成分がポリエチレンナフタレンジカルボキシレートであって、さらに層Ｂにおけるカルボキシホスフィン酸化合物またはカルボキシ亜ホスフィン酸化合物の少なくともいずれか１種に由来する成分のリン原子としての含有量が層Ｂを基準として０重量％以上１重量％以下かつ層Ａのリン原子含有量以下であること、ポリエステル層Ａとポリエステル層Ｂとが交互に３層以上積層された積層構成であること、の少なくともいずれか一つを具備するものを包含する。 The flame retardant polyester film for an electricity storage element electrode of the present invention is, as a preferred embodiment thereof, the carboxyphosphinic acid compound being a compound represented by the following formula (I):

Wherein R ¹ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ² and R ³ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom. X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{1 to} R ³ may be the same or different.
The carboxyphosphinic acid compound is a compound represented by the following formula (II):

(Wherein R ⁴ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ⁵ and R ⁶ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group, or a hydrogen atom) X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{4 to} R ⁶ may be the same or different.
The flame-retardant polyester film has a laminated structure in which a polyester layer B is further laminated on at least one surface of the polyester layer A, the main component of the polyester layer B is polyethylene naphthalene dicarboxylate, and the carboxyphosphine in the layer B The content as a phosphorus atom of a component derived from at least one of an acid compound or a carboxyphosphinic acid compound is 0% by weight or more and 1% by weight or less based on the layer B and less than or equal to the phosphorus atom content of the layer A In other words, the invention includes at least one of the following: a laminated structure in which three or more polyester layers A and polyester layers B are alternately laminated.

  Furthermore, as a preferred embodiment of the flame retardant polyester film for an electricity storage element electrode of the present invention, a conductive thin film is formed on at least one surface of the flame retardant polyester film, the conductive thin film is a metal thin film, metal The thin film is mainly composed of aluminum element, the metal thin film is composed mainly of copper element, the metal thin film is formed on both sides of the flame-retardant polyester film, and is formed on one side The metal thin film includes an aluminum element as a main component, and the metal thin film formed on the other surface includes at least one of a copper element as a main component.

The present invention also relates to an electrode for an electric storage element obtained by further laminating an electrode agent on the surface of the conductive thin film of the flame-retardant polyester film for an electric storage element electrode of the present invention. The main component of the electrode agent in the battery is a lithium / transition metal composite oxide, the main component of the electrode agent in the electrode for the storage element is carbon having an amorphous carbon structure, and the aluminum element of the flame retardant polyester film for the storage element electrode An electrode agent mainly composed of lithium / transition metal composite oxide is laminated on the surface of the metal thin film mainly composed of copper, and the carbon having the amorphous carbon structure is mainly disposed on the surface of the metal thin film mainly composed of copper element. It is used for laminated electrode materials, lithium ion secondary batteries or electric double layer capacitors. It include those comprising at least one of.
The present invention further relates to a power storage device in which the power storage device electrode of the present invention is incorporated.

  The flame retardant polyester film for power storage element electrode of the present invention is a thin polyester film that enables higher volume and weight energy density than conventional products, but has high puncture resistance and bending resistance suitable for power storage element electrode applications. In addition, since it has flame retardancy, it is possible to provide a film suitable for an electrode for an electricity storage element, particularly for a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor.

A cross-sectional view of the configuration of the lithium ion battery in the measurement method (10-1) is shown in FIG.

  The present invention will be described in detail below.

<Polyester layer A>
The flame-retardant polyester film of the present invention has at least one polyester layer A (hereinafter sometimes referred to as layer A) containing polyethylene naphthalene dicarboxylate as a main component, and the polyester layer A is a carboxyphosphinic acid compound or A component derived from at least one of carboxyphosphinic acid compounds (hereinafter sometimes referred to as phosphorus-based component P) in the range of 0.01% by weight to 3% by weight as phosphorus atoms with respect to the polyester layer A Including.
Here, “main” means 65% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, particularly preferably 85% by weight or more based on the weight of the layer A.
The polyethylene naphthalene dicarboxylate of the present invention is preferably polyethylene-2,6-naphthalene dicarboxylate.

（式中、Ｒ^１は炭素数１〜１０のアルキル基または炭素数６〜１８のアリール基、Ｒ^２およびＲ^３は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^１〜Ｒ^３はそれぞれ同一でも異なっていてもよい） Specific examples of the carboxyphosphinic acid compound contained as a flame retardant component derived from a phosphorus compound in the layer A include compounds represented by the following formula (I).

Wherein R ¹ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ² and R ³ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom. X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{1 to} R ³ may be the same or different.

（式中、Ｒ^４は炭素数１〜１０のアルキル基または炭素数６〜１８のアリール基、Ｒ^５およびＲ^６は炭素数１〜１８のアルキル基、アリール基、モノヒドロキシアルキル基または水素原子、Ｘは炭素数１〜１８の２価の炭化水素基をそれぞれ表わし、Ｒ^４〜Ｒ^６はそれぞれ同一でも異なっていてもよい） Specific examples of the carboxyphosphinic acid compound include compounds represented by the following formula (II).

(Wherein R ⁴ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ⁵ and R ⁶ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group, or a hydrogen atom) X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{4 to} R ⁶ may be the same or different.

  By using such a phosphorus compound as a flame retardant component, high flame retardancy is exhibited without the use of other phosphorus compounds, and there is little reduction in the bending resistance inherent in polyethylene naphthalene dicarboxylate. Have. On the other hand, when a phosphorus compound other than a carboxyphosphinic acid compound or a carboxyphosphinic acid compound is used, the mechanical properties of the polyester film are reduced by the flame retardant, and sufficient flame resistance cannot be obtained. It is difficult to balance sex.

  Examples of the carboxyphosphinic acid compound represented by the formula (I) include carboxymethylphenylphosphinic acid, (2-carboxyethyl) phenylphosphinic acid, (2-carboxyethyl) toluylphosphinic acid, (2-carboxyethyl) 2,5- Dimethylphenylphosphinic acid, (2-carboxyethyl) cyclohexylphosphinic acid, (3-carboxypropyl) phenylphosphinic acid, (4-carboxyphenyl) phenylphosphinic acid, (3-carboxyphenyl) phenylphosphinic acid, and their lower alcohols Examples include esters and lower alcohol diesters. Among these, particularly preferred compounds include (2-carboxyethyl) phenylphosphinic acid represented by the following formula (III), (3-carboxypropyl) phenylphosphinic acid represented by the following formula (IV), and 2-carboxyethylmethylphosphine. Examples include acid ethylene glycol esters. At least one of these carboxyphosphinic acid compounds is preferably used, and two or more of them may be used in combination.

  Further, as the carboxyphosphinic acid compound represented by the formula (II), carboxymethylphenylphosphinic acid, (2-carboxyethyl) phenylphosphinic acid, (2-carboxyethyl) toluylphosphinic acid, (2-carboxyethyl) ) 2,5-dimethylphenylphosphinic acid, (2-carboxyethyl) cyclohexylphosphinic acid, (3-carboxypropyl) phenylphosphinic acid, (4-carboxyphenyl) phenylphosphinic acid, (3-carboxyphenyl) Examples thereof include phenylphosphinic acid and lower alcohol esters and lower alcohol diesters thereof.

These phosphorus-based components P are contained in the range of 0.01 wt% or more and 3 wt% or less as phosphorus atoms with respect to the weight of the polyester layer A. The lower limit of the content of the phosphorus component P is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and particularly preferably 0.7% by weight or more. The upper limit of the content of the component is preferably 2.0% by weight or less, more preferably 1.5% by weight or less, and particularly preferably 1.0% by weight or less.
When the content of these phosphorus-based components P is less than the lower limit value, sufficient flame retardancy is not exhibited as a film, whereas when the content exceeds the upper limit value, the bending resistance inherent in polyethylene naphthalenecarboxylate is reduced. Connected.

  Moreover, in the flame-retardant polyester film of the present invention, the phosphorus component P is preferably copolymerized as a polyester copolymer component in a range of 30 to 100 mol% with respect to the total amount contained in the layer A, More preferably, it is 60-100 mol%, Most preferably, it is 80-100 mol%. When the phosphorus component P is copolymerized with the polyester within the above range, high flame retardancy can be obtained while suppressing bleed-out of the phosphorus component.

Polyethylene naphthalene dicarboxylate is a conventionally known method, for example, a method of directly obtaining a low polymerization degree polyester by reaction of dicarboxylic acid and glycol, or a reaction of lower alkyl ester of dicarboxylic acid and glycol using a conventionally known transesterification catalyst. And then a polymerization reaction is performed in the presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony compound, a germanium compound, or a titanium compound can be used.
The phosphorus component P is added at any time during the production of the polyester, but a more preferable addition time is after the completion of the first stage reaction for producing a low polymer by esterification or transesterification, This is until the start of the second stage in which the obtained low polymer is subjected to a polycondensation reaction. By adding the phosphorus-based component P at this time, it becomes easy to exist as a polyester copolymer component.
For the purpose of deactivating the transesterification catalyst, a phosphorus compound usually used as a deactivator of the transesterification catalyst in the polycondensation step may be used as a phosphorus element within a very small range of 100 ppm or less. The amount is extremely small and is not added for the purpose of imparting flame retardancy.

The polyethylene naphthalene dicarboxylate used for the layer A can further have a copolymer component other than the phosphorus-based component P within a range of 10 mol% or less based on the total dicarboxylic acid component. As a copolymer component constituting the copolymer, a compound having two ester-forming functional groups in the molecule can be used. Succinic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid, terephthalic acid 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, tetralindicarboxylic acid, decalindicarboxylic acid, diphenyletherdicarboxylic acid and other dicarboxylic acids, p-oxy Oxycarboxylic acids such as benzoic acid and p-oxyethoxybenzoic acid, or ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanedimethanol, neopentyl glycol, bisphenol sulfo Diols such as ethylene oxide adduct of bisphenol A, ethylene oxide adduct of bisphenol A, diethylene glycol and polyethylene oxide glycol can be preferably used. These copolymer components may be used alone or in combination of two or more.
Among these copolymer components, preferred acid components are isophthalic acid, terephthalic acid, 4,4′-diphenyldicarboxylic acid, 2,7-naphthalenedicarboxylic acid, p-oxybenzoic acid, and preferred diol components. Is an ethylene oxide adduct of trimethylene glycol, hexamethylene glycol, neopentyl glycol, bisphenol sulfone. These copolymer components may be copolymerized as monomer components, or may be copolymerized by transesterification with other polyesters.

  The intrinsic viscosity of polyethylene naphthalene dicarboxylate is preferably 0.40 dl / g or more, more preferably 0.40 to 0.90 dl / g in o-chlorophenol at 35 ° C. When the intrinsic viscosity is less than 0.40 dl / g, it may be difficult to reduce the thickness required for an electrode substrate film while frequently causing process cutting, bending resistance, puncture resistance, and the like. If the intrinsic viscosity is higher than 0.9 dl / g, melt extrusion is difficult and the polymerization time is long and uneconomical.

  The layer A constituting the flame retardant polyester film may further contain a resin component other than the above polyethylene naphthalene dicarboxylate. For example, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, Examples include polycarbonate, polyarylate, polyetherimide, polyphenylene ether, and phenoxy resin. Such a resin can be used in an amount of preferably 30% by weight or less, more preferably 20% by weight or less based on the weight of the layer A. When such a resin is used in excess of the upper limit, the physical properties inherent to polyethylene naphthalene dicarboxylate may be impaired.

<Polyester layer B>
The flame-retardant polyester film of the present invention may have a laminated structure. In the case of a laminated structure, a polyester layer B (hereinafter sometimes referred to as layer B) is further laminated on at least one surface of the layer A, and the polyester The main component of the layer B is polyethylene naphthalene dicarboxylate, and the content of the component derived from at least one of the carboxyphosphinic acid compound and the carboxyphosphinic acid compound in the layer B is the layer B. It is preferable that the content is 0% by weight or more and 1% by weight or less and not more than the phosphorus atom content of layer A as a reference.
Here, “main” means that the content of polyethylene naphthalene dicarboxylate is 80% by weight or more, more preferably 90% by weight or more, particularly preferably 95% by weight or more based on the weight of the layer B.
By further including the layer B that does not contain the phosphorus-based component P or has a low content, the original bending resistance of polyethylene naphthalene dicarboxylate can be further maintained.

  The polyethylene naphthalene dicarboxylate constituting the layer B is preferably polyethylene-2,6-naphthalene dicarboxylate. Copolymerization components other than the phosphorus-based component P of the polyester, production methods and the like are the same as those for the polyethylene naphthalene dicarboxylate of the layer A.

The specific type of the phosphorus component P conforms to the description of the phosphorus component P of the layer A. The content of the phosphorus component P is preferably 0% by weight or more and 1% by weight or less based on the weight of the layer B and less than or equal to the phosphorus atom content of the layer A. The content is more preferably 0.5% by weight or less, further preferably 0.4% by weight or less, and particularly preferably 0.2% by weight or less.
The polyester layer B is 20% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less based on the weight of the layer B, and is a thermoplastic resin other than inert particles and polyethylene naphthalene dicarboxylate. In addition, other additives may be contained.

<Other ingredients>
In order to improve the handleability of the film, inert particles or the like may be added to the flame-retardant polyester film of the present invention within a range not impairing the effects of the invention. Examples of the inert particles include inorganic particles (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide) containing the elements of Periodic Tables IIA, IIB, IVA, and IVB, and crosslinked silicone resins. , Particles made of a polymer having high heat resistance such as crosslinked polystyrene and crosslinked acrylic resin particles.
When the inert particles are contained, the average particle diameter of the inert particles is preferably in the range of 0.001 to 5 μm, and preferably in the range of 0.01 to 10% by weight with respect to the total weight of the film. More preferably, it is 0.05-5 weight%, Most preferably, it is 0.05-3 weight%.
Moreover, when a flame-retardant polyester film has a laminated structure of two or more layers, the inert particles may be blended in any layer.

<Crystal orientation>
The flame-retardant polyester film of the present invention has a degree of coincidence (referred to as crystal orientation) of a crystal plane normal corresponding to a diffraction peak with a Bragg angle of 25 ° to 29 ° obtained by wide-angle X-ray diffraction measurement. Is 0.95 or more.
The crystal plane corresponding to the diffraction peak with a Bragg angle of 25 to 29 ° defined in the present invention is 0.31 to 0.36 nm in terms of the crystal plane spacing, and the ethylene naphthalene dicarboxylate component constituting the polyester of the present invention This corresponds to the interval between the stacked naphthalene rings in the crystal structure. That is, the crystal plane (the (−110) plane in the crystal lattice of the ethylene naphthalene dicarboxylate component, Bragg angle = about 27 °) is substantially parallel to the naphthalene ring in the polyester molecular chain.

Specifically, the degree of crystal orientation is obtained by quantifying the degree of coincidence between the normal to the crystal plane of the naphthalene ring in the polyester molecular chain and the direction perpendicular to the film plane, often referred to as the z-axis. That the degree of coincidence of the crystal plane normal to the film plane normal (z direction) is 0.95 or more means that the naphthalene ring in the molecular chain in the polyester film of the present invention is located parallel to the film plane. (Hereinafter, such a molecular orientation state is sometimes expressed as “high degree of plane orientation”).
The degree of crystal orientation is determined by measuring the X-ray diffraction pole figure by rotating a sample fixed at a Bragg angle corresponding to the crystal plane to be observed over the whole sphere by wide-angle X-ray diffraction measurement. From the distribution behavior, the degree of coincidence with the axis of the film to be evaluated (in the present invention, the film surface normal (z direction)) is calculated.
The calculated degree of crystal orientation takes a value of -0.5 to 1, and the closer the degree of crystal orientation is to 1, the more the distribution in which the normal vector of the measured crystal plane is parallel to the evaluated direction is distributed. The closer the degree of orientation is to -0.5, the more distributed the normal vector of the measured crystal plane and the evaluation direction are orthogonal.

Since the naphthalene ring has a rigid molecular structure, a film with a high degree of plane orientation having a crystal orientation of 0.95 or more is highly resistant to damage in the direction of the film surface such as piercing, and has a thinned electrode substrate. Sufficient puncture resistance is exhibited as a material. In particular, in the case of a flame-retarded film as in the present invention, the mechanical strength tends to decrease, but by using the phosphorus-based component P of the present invention as a flame retardant component and further increasing the crystal orientation of the film. In addition, sufficient puncture resistance is developed as a thinned electrode substrate. If the degree of crystal orientation is less than the lower limit, sufficient puncture resistance cannot be obtained.
The preferable range of the crystal orientation is 0.975 or more, more preferably 0.985 or more.

  In order to obtain a film having such a degree of crystal orientation, as described in detail in the film production method, the film longitudinal direction (hereinafter sometimes referred to as film continuous film-forming direction, longitudinal direction or MD direction) and film width direction ( Hereinafter, the stretching ratio of the direction perpendicular to the film longitudinal direction, the transverse direction or the TD direction) may be more than 3.6 times and not more than 8.0, preferably 3.8 times or more and 7. It is achieved by performing the stretching treatment in a range of 0 times or less, more preferably 3.9 times or more and 6.0 times or less.

<Out-of-plane birefringence>
The flame retardant polyester film of the present invention preferably has an out-of-plane birefringence of 0.25 or more, and more preferably 0.27 or more. Further, the upper limit value of the out-of-plane birefringence is limited to the value of the α-type single crystal having a crystallinity of 100%, and is in the range of 0.42 or less.
The degree of crystal orientation described above is a molecular orientation focusing on the crystalline region, whereas the out-of-plane birefringence is a characteristic that defines the overall molecular orientation including the amorphous region in addition to the crystalline region. Defined in 1).
Ns = (n _MD + n _TD ) / 2−n _Z (1)
(In the above formula, Ns represents out-of-plane birefringence, n _MD represents the refractive index in the MD direction, n _TD represents the refractive index in the TD direction, and n _Z represents the refractive index in the film thickness direction.)

  By having out-of-plane birefringence within such a range, it has excellent puncture resistance when used as a thin electrode substrate. The specific means for obtaining such out-of-plane birefringence characteristics can use the same method as the degree of crystal orientation, and the naphthalene ring of the ethylene naphthalene dicarboxylate component has a large polarizability in the ring plane direction. Since it has a small polarizability in the linear direction, the value of out-of-plane birefringence is increased by orienting the naphthalene ring in parallel to the film surface regardless of the crystalline or amorphous part due to molecular orientation by stretching.

<Film thickness>
The flame-retardant polyester film of the present invention has a film thickness of 0.2 μm or more and 30 μm or less. If a thick film exceeding the upper limit is used as the electrode base material, it becomes thicker than the conventional metal foil, and does not lead to an improvement in the energy density of the electricity storage device, particularly the volume energy density. On the other hand, when the film thickness is so thin that it does not reach the lower limit, the production of the film becomes extremely difficult. The film thickness is more preferably 0.2 μm or more and 20 μm or less, further preferably 0.2 μm or more and 12 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less. Even when the flame-retardant polyester film of the present invention has a laminated structure, the film thickness is preferably within the range.

<Heat shrinkage>
In the flame-retardant polyester film of the present invention, the film shrinkage ratio after unrestrained heat treatment at 150 ° C. for 30 minutes is 5% or less in both the film MD direction and the film TD direction. In order to prevent short circuit, etc., the reaction area can be stabilized. Such thermal shrinkage is more preferably 3% or less, and particularly preferably 2% or less.
As a means for obtaining these heat shrinkage characteristics, it is preferable to perform heat setting treatment on the stretched film in the range of not less than the glass transition point of the polyester and not more than (melting point−15 ° C.). Moreover, you may attach toe-in within the range by which the optical axis stability of the both ends of a film is not impaired by a bowing phenomenon.

<Layer structure>
The flame-retardant polyester film of the present invention is characterized by having at least one polyester layer A containing a predetermined amount of a phosphorus-based component P corresponding to a flame-retardant component and having a certain degree of crystal orientation. By having such a layer, when used as a substrate film for a storage element electrode, a flame retardant function is exhibited upon ignition due to a short circuit, and at the same time, high puncture resistance and bending resistance suitable for storage element electrode applications It has.

In the flame-retardant polyester film of the present invention, the content of the phosphorous component P is at least 0% by weight and not more than 1% by weight on at least one side of the layer A, and the phosphorous atom content of the layer A is not more than the main component. It is preferable that the layer B which is the naphthalene dicarboxylate is further laminated.
In addition, when the flame-retardant polyester film of the present invention further has a layer B, it has a two-layer structure such as a layer A | layer B or a laminated structure in which three or more layers A and B are alternately laminated. May be. For example, in the case of three layers, layer A | layer B | layer A, layer B | layer A | layer B are exemplified.

In the case of three or more layers, the number of layers may be 11 or more. The greater the number of layers, the better the bending resistance and puncture resistance.
The upper limit of the number of layers is not particularly limited, but if the bending resistance and puncture resistance effects exceed a certain number of layers, the further effect is poor, and the merging device for both resins for layer A and layer B From the viewpoint of the size, it is limited to 2001 layers or less. The number of stacked layers is further limited to 1001 layers or less, usually 201 layers or less.

The layer thickness ratio of layer A and layer B is not particularly limited, but the ratio of the total thickness of layer A to the total thickness of layer B is in the range of 1: 5 to 5: 1. It is preferable from the point of balance of strength characteristics.
In the case of a laminated structure having the layer B, the layer A mainly has a function of expressing flame retardancy, and the layer B can further improve the bending resistance and workability.

<Film surface processing>
The flame-retardant polyester film of the present invention may be surface-treated for the purpose of improving adhesiveness with a conductive thin film described later. The method of surface treatment is not particularly limited, but preferred examples include easy-contact layer application, corona treatment, and plasma treatment. These surface treatments may be performed in the process of forming a film, or may be performed in a process different from the film forming process.

<Conductive thin film>
In the flame-retardant polyester film of the present invention, a conductive thin film is preferably formed on at least one surface. In order to use the polyester film of the present invention as an electrode base film having a function as a current collector in a power storage device, an electrode agent is provided on the film by coating or the like. However, in many cases, such electrode agent layers are formed by joining fine particles of an electrode agent compound with a binder resin, and collecting current from one end of the layer increases internal resistance. As a result, voltage loss may occur.
Therefore, in providing the electrode agent layer, by first providing a conductive thin film on at least one surface of the flame retardant polyester film to impart conductivity, and providing the electrode agent layer on the conductive thin film, It is possible to collect current, and loss due to internal resistance can be reduced. That is, by forming a conductive thin film on at least one surface of the polyester film, the electrical connection between the electrode agent and the polyester film can be enhanced via the conductive thin film, and it can function sufficiently as an electrode of a storage element. Can be made.

  In order to obtain sufficient conductivity, the conductive thin film is preferably a metal thin film. The metal forming the thin film is not particularly limited as long as it is conductive for the purpose of the present invention. For example, aluminum, nickel, gold, silver, copper, cadmium, etc. are mentioned. From the viewpoint of high conductivity, film formation, handling, and stability, that is, the potential difference between the positive and negative electrodes (called “potential window”) to prevent the electrode agent compound from causing an undesirable reaction. In the case where the element is a lithium ion secondary battery, it is preferable to use a positive electrode having an aluminum element as a main component and a negative electrode having a copper element as a main component. Moreover, when an electrical storage element is an electric double layer capacitor, since an electrochemical reaction does not occur, any of the exemplified metal thin films may be used, and the same type of metal thin film may be used for both electrodes.

The thickness of the conductive thin film is preferably in the range of 1 nm to 5000 nm, and more preferably in the range of 10 nm to 5000 nm for the purpose of suppressing the internal resistance heat generation of the battery. Further, from the viewpoint of contribution to weight reduction and bending resistance of the thin film, the thickness is more preferably from 10 nm to 3000 nm.
The method for producing the conductive thin film is not limited, and examples thereof include plating, vacuum deposition, electroplating, and sputtering.
Specific examples of the conductive thin film other than the metal thin film may be an inorganic conductor such as a metal oxide or an organic conductor.

Moreover, the electroconductive thin film of this invention may be formed in the at least one surface of the polyester film, and may be laminated | stacked on both surfaces. When laminating a conductive thin film on both surfaces of a film, the same kind of material may be used, or different materials may be used.
For example, a metal thin film containing a copper element as a main component can be formed on one or both sides of a polyester film, and a negative electrode agent described later can be further laminated thereon to be used as a negative electrode.
Further, for example, a metal thin film mainly composed of an aluminum element can be formed on one side or both sides of a polyester film, and a positive electrode agent described later can be further laminated thereon to be used as a positive electrode. .

Furthermore, as a specific example in which a metal thin film is formed on both sides of a polyester film and the both sides are of different materials, the metal thin film formed on one side is mainly composed of aluminum element and formed on the other side. An embodiment in which the metal thin film to be formed is mainly composed of a copper element. In this case, by laminating an electrode agent for a positive electrode on a metal thin film containing aluminum as a main component, one surface functions as a positive electrode, while the metal thin film containing a copper element as a main component is used. By laminating an electrode agent for a negative electrode thereon, the opposite surface can function as a negative electrode.
In the case of such a structure in which different types of metal thin films are formed on both sides, particularly when used as an electrode base material of a lithium ion secondary battery, an aluminum layer that is a positive electrode current collector and a copper layer that is a negative electrode current collector are: Since it is separated by the polyester film which is an insulator, there is an advantage that the possibility of a short circuit is reduced. Also, when a battery is manufactured by winding or laminating after laminating with a separator, an electrolyte layer, etc., the number of constituent elements is less than that of the conventional product, which is excellent in productivity and extremely preferable.

<Electrode for power storage element and power storage element>
By forming a conductive thin film on at least one surface of the flame retardant polyester film for an electricity storage device electrode of the present invention and further laminating an electrode agent on the surface, it can be used as an electrode for an electricity storage device.
By using the flame retardant polyester film for an electricity storage element electrode of the present invention as an electrode base material layer, the volume energy density of the electricity storage element can be improved by making the base material thinner than a conventional metal base material. In addition, by using a polyester film instead of the metal substrate, it is possible to improve the weight energy density of the electricity storage element by reducing the weight of the electrode substrate.
Furthermore, by using the flame retardant polyester film for an electricity storage element electrode of the present invention as an electrode base material layer, it has excellent puncture resistance and bending resistance while being a thin resin base material, so that short-circuiting due to conduction is prevented. It can be prevented, and can exhibit a flame retardant function even in the event of ignition due to a short circuit.

  When used as an electrode of a lithium ion secondary battery, it is preferable to stack an electrode agent having an intercalation function for lithium ions. Specific examples of such an electrode agent include those conventionally known, for example, an electrode agent mainly composed of a lithium / transition metal composite oxide such as lithium cobaltate, lithium nickelate and lithium manganate for a positive electrode, For the negative electrode, an electrode agent mainly composed of carbon having an amorphous carbon structure such as graphite and carbon nanotube can be used.

The positive electrode agent is formed on the surface of a conductive thin film such as an aluminum metal thin film. Moreover, the electrode agent for negative electrodes is formed on the surface of electroconductive thin films, such as a copper metal thin film. Specifically, an electrode agent mainly composed of a lithium / transition metal composite oxide is laminated on the surface of a metal thin film mainly composed of an aluminum element of a flame retardant polyester film for a storage element electrode, and a component mainly composed of a copper element. An electrode for a secondary battery in which an electrode agent mainly composed of carbon having an amorphous carbon structure is laminated on the surface of the metal thin film is exemplified.
The method for laminating the electrode agent on such a conductive thin film is not particularly limited, and examples thereof include a method in which a raw material for the electrode agent is mixed with polyvinylidene fluoride or styrene butadiene rubber and applied.

The present invention also includes a power storage element in which such a power storage element electrode is incorporated. The power storage element has at least one power storage element electrode, and a separator, an electrolyte layer, or the like is laminated on one or both sides of the power storage element. A power storage device manufactured by times or lamination is exemplified.
As a specific configuration of the electrode for the storage element, a configuration in which a conductive thin film is formed on one side of the flame retardant polyester film for the storage element electrode of the present invention, and an electrode agent is laminated thereon, or the same kind on both sides of the polyester film is used. In the case of a configuration in which a conductive thin film is formed and the same type of electrode agent is laminated on both surfaces, one electrode member functions as one pole. In such a case, by using at least one electrode member prepared for the positive electrode and at least one electrode member prepared for the negative electrode, and further having at least one separator layer, a function as a power storage element is achieved.

  In addition, as another specific configuration of the electrode for the storage element, different types of conductive thin films are formed on both sides of the flame retardant polyester film for the storage element electrode of the present invention, and an electrode agent suitable for each electrode is further laminated. When one is a positive electrode and the other is a negative electrode, at least one of the electrode members is used, and at least one separator is provided, so that a function as a power storage element is achieved.

When used as an electrode for a lithium ion capacitor, a lithium ion capacitor can be prepared by using an electrolyte of a lithium salt in combination with an electrode similar to that for a lithium ion secondary battery negative electrode.
When used as an electrode of an electric double layer capacitor, in order to generate a sufficient amount of an electric double layer at the electrolyte interface in contact with the electrode, the conductive thin film surface of the film of the present invention has a conductive and main component of activated carbon. A substance having a large surface area (porous carbon or the like) is preferably laminated as an electrode agent.

  The electricity storage device obtained by using the electrode for electricity storage device comprising the flame retardant polyester film for electricity storage device electrode of the present invention as an electrode base material layer is capable of higher volume and weight energy density than conventional products, and moreover than before Although it is a thin substrate layer, it has high piercing resistance and bending resistance, so it can prevent short circuit due to conduction, and can also exhibit a flame retardant function even in the event of ignition due to a short circuit. It is excellent in safety. Specific examples of the power storage element include a secondary battery and a capacitor, and more specifically, a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor.

<Film production method>
Examples of the method for producing the polyester film of the present invention include a biaxially stretched film production method in which a sheet obtained by melt-extruding and solidifying polyester is stretched in two directions, ie, the film longitudinal direction and the width direction.
The film-forming method can be manufactured using a known film-forming method. For example, after sufficiently drying the copolyester containing the phosphorus-based component P prepared for the layer A, the melting point to (melting point + 70) ° C. Melt in the extruder at a temperature of Moreover, in the case of the laminated | multilayer film which laminated | stacked the layer B, after fully drying the polyester adjusted for the layer B, it is supplied to another extruder and is made to melt | dissolve at the temperature of melting | fusing point- (melting | fusing point +70) degreeC.

  The molten resin is formed into a sheet through a T-die and cooled with a cooling drum to produce an unstretched film. In the case of a laminated film, a laminated unstretched film is produced by a method of laminating both molten resins inside a die, for example, a simultaneous laminated extrusion method using a multi-manifold die. According to this simultaneous lamination extrusion method, the melt of the resin forming one layer and the melt of the resin forming another layer are laminated inside the die, and formed into a sheet form from the T-die while maintaining the laminated form. Is done.

  Next, the unstretched film can be produced by a method of sequentially biaxially stretching or simultaneously biaxially stretching and heat-setting. In the case of forming a film by sequential biaxial stretching, the film stretching temperature is preferably a temperature of the glass transition point (Tg) to (Tg + 40 ° C.) of the polyester. Moreover, it is necessary to perform a extending | stretching process in the range from which a draw ratio exceeds 3.6 times and becomes 8.0 or less in both the film longitudinal direction and a film width direction. By highly stretching in two directions, the crystal orientation of the present invention can be achieved. The draw ratio is preferably 3.8 times or more and 7.0 times or less, and more preferably 3.9 times or more and 6.0 times or less.

In addition, when the stretching is performed, when the stretching ratio in the film longitudinal direction and the film width direction represented by the following formula (2) is more than 0.75 and 1.33 or less, the molecular chain direction is biased in one direction. It is possible to prevent a drop in the piercing strength due to the above.
Film stretch ratio = R ^TD / R ^MD (2)
(In the above formula, R ^TD represents the stretching ratio in the film width direction, and R ^MD represents the stretching ratio in the film longitudinal direction.)

After the stretching, it is preferable to further perform a heat setting treatment. The lower limit value of the heat setting temperature is preferably a glass transition point of the polyester, and the upper limit value of the heat setting temperature is preferably 15 ° C. lower than the melting point of the polyester. The heat setting temperature is more preferably 180 ° C. or higher and 240 ° C. or lower. By performing such heat setting treatment, it is possible to obtain the heat shrinkage characteristic defined in the present invention.
The stretched film may be subjected to post-processing such as surface activation treatment (coating, corona discharge, plasma treatment, etc.) as necessary, such as improvement in adhesion at the time of pasting with another member. This post-processing may be performed during the film stretching process or may be performed in a separate process.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Polyester component About each layer of the film sample, the component of the polyester and the copolymerization component were specified by ¹ H-NMR measurement.

(2) Method for measuring phosphorus content The phosphorus atom content of the obtained polyester was measured by fluorescent X-rays.

(3) Film thickness A film sample is sandwiched between spindle detectors (K107C manufactured by Anritsu Electric Co., Ltd.), and 10 points of thickness are measured at different positions using a digital differential electronic micrometer (K351 manufactured by Anritsu Electric Co., Ltd.). Then, the average value was obtained and defined as the film thickness.

(4) Degree of crystal orientation Method of crystal plane to be evaluated for film samples by wide-angle X-ray diffraction pole measurement using an X-ray diffractometer (ROTAFLEX RINT2500HL manufactured by Rigaku Corporation) and a pole sample table (multipurpose sample table manufactured by Rigaku Corporation) <Cos ² Φ _Z >, which is the integral average value of the direction cosine of the line vector in the film thickness direction, was determined, and the degree of crystal orientation (−110) was determined from the following equation (3).
fc _Z = 2/3 <cos ² Φ _Z > −1/2 (3)
The crystal plane to be evaluated was determined by the following method. About the obtained film, wide-angle X-ray diffraction 2θ-θ scan (reflection method) using a powder X-ray diffractometer (Rigaku Denki RINT2500HL) (X-ray source CuK-α, divergence slit 1/2 °, scattering slit 1 / 2 °, receiving slit 0.15 mm, scan speed 1.000 ° / min), and 2θ dependence of diffraction intensity is measured, and the Pseudo Voice peak model is used for the largest diffraction peak between Bragg angle 25 ° to 29 ° The peak position is detected after separating the diffraction peak derived from the crystal plane from the halo and background derived from the amorphous surface by the multiple peak separation method, and the optical system is fixed at the angle in the above-mentioned extreme point measurement. did. The crystal plane in the examples of the present invention is considered to be mostly derived from the (-110) plane in the crystal lattice of poly (ethylene-2,6-naphthalenedicarboxylate), and the Bragg angle is about 27. °.

(5) Out-of-plane birefringence About the obtained film, the refractive index with respect to NaD line | wire (589.3 nm) was measured with the following method, and it used for calculation of out-of-plane birefringence. That is, the refractive indexes nx, ny, and nz in the three directions of the film measured with a refractometer (manufactured by Metricon, prism coupler) with three types of laser light having wavelengths of 473 nm, 633 nm, and 830 nm are shown below. Cauchy's refractive index chromatic dispersion fitting equation n _i (λ) = a / λ ⁴ + b / λ ² + c
(Where n _i (λ): refractive index in each direction at wavelength λ (nm) (i = MD, TD, Z), a, b, c: constants, respectively)
And the constants of a, b, and c are obtained from the obtained three equations, and then the refractive index at 589.3 nm (n _MD (589.3), n _TD (589.3), n _Z (589) .3)) was calculated. Out-of-plane birefringence Ns was calculated from the obtained refractive index according to the following formula.
Ns = (n _MD + n _TD ) / 2−n _Z
(In the above formula, Ns represents out-of-plane birefringence, n _MD represents the refractive index in the MD direction, n _TD represents the refractive index in the TD direction, and n _Z represents the refractive index in the film thickness direction.)

(6) Heat shrinkage rate A 30 cm square film in which the longitudinal direction (MD direction) and the lateral direction (TD direction) of the film are marked in an oven set at a temperature of 150 ° C., and an accurate length is measured in advance. Is loaded with no load, taken out after holding for 30 minutes, returned to room temperature, and the change in dimensions is read. From the length (L ₀ ) before the heat treatment and the dimensional change (ΔL) due to the heat treatment, the thermal shrinkage rates (%) in the MD direction and the TD direction were obtained from the following formula (4).
Thermal contraction rate = (ΔL / L ₀ ) × 100 (4)

(7) Puncture strength Measured according to JAS P1019. The obtained film sample was fixed in a plane, and a semicircular needle having a diameter of 1.0 mm and a tip shape radius of 0.5 mm was pierced at a speed of 50 ± 0.5 mm per minute perpendicular to the sample surface. The maximum load until penetrating was measured and used as the piercing strength.

(8) Bending strength Using a MIT folding resistance tester, the number of times of bending until the film sample broke was measured according to JIS C5016 at a bending portion polar radius of 0.38 mm, a load of 10 N, and a bending speed of 175 cpm. .

(9) Flame retardancy Evaluation was made according to the UL-94 VTM method. The obtained film was cut into 20 cm × 5 cm and allowed to stand in 23 ± 2 ° C. and 50 ± 5% RH for 48 hours. Thereafter, the lower end of the sample was separated from the burner by 10 mm and held vertically. The bottom end of the sample was indirectly heated for 3 seconds using a Bunsen burner having an inner diameter of 9.5 mm and a flame length of 19 mm as a heating source. Flame retardancy was evaluated according to the evaluation criteria of VTM-0, VTM-1, and VTM-2.

(10) Evaluation of Lithium Ion Battery (10-1) Production of Lithium Ion Battery An aluminum thin film having a thickness of 500 nm was formed on both surfaces of the films obtained in Examples and Comparative Examples by vacuum deposition. The surface of the aluminum thin film so as to have a thickness of 100 μm after drying using a slurry prepared by mixing lithium cobaltate powder with an N-methylpyrrolidone solution of polyvinylidene fluoride so that the lithium cobaltate content after drying is 95 wt% After coating, drying and calendering, it was cut into a size of 21 cm × 30 cm to prepare a positive electrode.
Moreover, as a sample for negative electrodes, a copper thin film having a thickness of 250 nm was formed on both surfaces of the films obtained in Examples and Comparative Examples by sputtering. Using a slurry prepared by mixing graphite powder with an aqueous dispersion of styrene butadiene rubber latex so that the graphite content after drying is 95 wt%, it is applied to the surface of the copper thin film so that the thickness after drying is 100 μm, dried, After calendering, it was cut into a size of 21 cm × 30 cm to prepare a negative electrode.
As shown in Fig. 1, 20 sets of separators (20cm x 30cm) made of porous polyethylene film are laminated as shown in Fig. 1, attached with leads, and stored in a polyethylene laminated container. After that, an electrolytic solution (an organic solvent of lithium hexafluorophosphate (ethylene carbonate + diethyl carbonate = 1: 1) solution (concentration: 1 mol / L)) was filled, and the container was sealed to prepare a test battery.

(10-2) Long-term durability Deterioration cycle until 50 batteries prepared by the procedure of (10-1) are repeatedly charged / discharged under the condition of 100 ° C. and a short circuit occurs in 10% of the total number of batteries. Is determined to be good (denoted as “◯” in Table 1) at 500 times or more, and defective (×) when the deterioration cycle is less than 500 times.

(10-3) Puncture resistance For the battery created in the procedure of (10-1), a fully charged battery sample equipped with a voltmeter is fixed in a planar shape, and the diameter is 2.5 mm perpendicular to the sample surface. The iron nail needle was pierced at a speed of 50 ± 0.5 mm per minute, and the load accompanying the nail penetration was measured while monitoring the voltage. When a large change in voltage due to penetration of the nail is observed, a load of 20 kg or more is good (“◯” in Table 1), and a load of less than 20 kg is bad (“×” in Table 1). To do.

[Example 1]
After 100 parts by weight of naphthalene-2,6-dicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol were transesterified according to a conventional method using 0.03 parts by weight of manganese acetate tetrahydrate as a transesterification catalyst, 0.07 part by weight of spherical silica particles having an average particle size of 0.3 μm dispersed in glycol was added. Subsequently, 6 parts by weight of 2-carboxyethylphenylphosphinic acid represented by the following formula (III) is added, 0.024 part by weight of antimony trioxide is added, and then polycondensation reaction is performed in a conventional manner under high temperature and high vacuum. To obtain a polyester having an intrinsic viscosity of 0.61 dl / g. The phosphorus atom concentration in the polyester was as shown in Table 1.

The obtained polyester was dried with a 180 ° C. dryer for 6 hours, put into an extruder, melt-kneaded at 295 ° C., and formed into a sheet form from a 290 ° C. die. This melt was extruded onto a rotary cooling drum having a surface temperature of 60 ° C. to obtain an unstretched film having a thickness of 88 μm.
The obtained unstretched film was led to a roll group heated to 140 ° C., stretched 4.1 times in the longitudinal direction (longitudinal direction), and cooled with a roll group at 60 ° C. Subsequently, the both ends of the longitudinally stretched film were guided to a tenter while being held by clips, and stretched 4.3 times in a direction (lateral direction) perpendicular to the longitudinal direction in an atmosphere heated to 150 ° C. Thereafter, heat setting was performed at 230 ° C. in a tenter, and after 3% relaxation at 180 ° C., the film was uniformly removed and cooled to room temperature to obtain a biaxially stretched film having a thickness of 4.5 μm. The properties of the obtained film are shown in Table 1.

[Example 2]
The polyester obtained by the same method as in Example 1 was dried with a 180 ° C. dryer for 6 hours, then charged into an extruder, and melt-kneaded at 295 ° C. (Layer A).
On the other hand, the polyester for layer B was obtained by the following method. After 100 parts by weight of naphthalene-2,6-dicarboxylic acid dimethyl ester and 60 parts by weight of ethylene glycol were transesterified according to a conventional method using 0.03 part by weight of manganese acetate tetrahydrate as a transesterification catalyst, The transesterification reaction was substantially stopped by adding 0.023 part by weight of phosphate. Subsequently, 0.024 parts by weight of antimony trioxide was added, and subsequently a polycondensation reaction was carried out in a conventional manner under high temperature and high vacuum to obtain a polyethylene having an intrinsic viscosity of 0.61 dl / g and a diethylene glycol copolymerization amount of 1.3 mol%. 2,6-Naphthalenedicarboxylate (PEN) was obtained. The obtained polyethylene-2,6-naphthalene dicarboxylate was dried with a 180 ° C. dryer for 6 hours and then charged into the other extruder (layer B), and laminated in three layers in a melted state (thickness ratio layer A). : Layer B: layer A = 1: 8: 1), and after forming into a sheet form from a die while maintaining such a laminated structure, an unstretched film was obtained in the same manner as in Example 1. The film thickness was 80 μm.
A stretched film was obtained under the same conditions as in Example 1 except that the stretching ratio was 3.9 times in the longitudinal direction and 4.1 times in the transverse direction. The properties of the obtained film are shown in Table 1.

[Example 3]
As the phosphorus compound used for the polyester of the layer A, 2-carboxyethylmethylphosphinic acid ethylene glycol ester represented by the following formula (V) was used instead of the phosphorus compound (III), and the phosphorus atomic weights in Table 1 were changed. Obtained a stretched film by the same method as in Example 2. The properties of the obtained film are shown in Table 1. In addition, the intrinsic viscosity of the polyester for layer A was 0.61 dl / g.

[Example 4]
As the phosphorus compound used for the polyester of layer A, 2-carboxyethylphenylphosphinic acid represented by the following formula (VI) was used in place of the phosphorus compound (III), and the phosphorus atomic weight was changed to that shown in Table 1. A stretched film was obtained in the same manner as in Example 2. The properties of the obtained film are shown in Table 1. In addition, the intrinsic viscosity of the polyester for layer A was 0.61 dl / g.

[Example 5]
A stretched film was obtained in the same manner as in Example 2 except that the amount of the phosphorus compound in layer A was changed and changed to the phosphorus atomic weight shown in Table 1. The properties of the obtained film are shown in Table 1. In addition, the intrinsic viscosity of the polyester for layer A was 0.61 dl / g.

[Example 6]
A stretched film was obtained in the same manner as in Example 2 except that the thickness of the unstretched film was 65 μm and the stretch ratio was 3.7 times in the longitudinal direction and 3.9 times in the transverse direction. The properties of the obtained film are shown in Table 1.

[Comparative Example 1]
A stretched film was obtained in the same manner as in Example 1, except that the polyester for layer B of Example 2 was used instead of the polyester used in Example 1. The properties of the obtained film are shown in Table 1. Since it did not contain a phosphorus component, it was inferior in flame retardancy.

[Comparative Example 2]
A stretched film was obtained in the same manner as in Example 2 except that the thickness of the unstretched film was 36.5 μm and the stretch ratio was 2.8 times in the longitudinal direction and 2.9 times in the transverse direction. The properties of the obtained film are shown in Table 1. The degree of crystal orientation was not sufficient, and sufficient piercing characteristics could not be obtained.

[Comparative Example 3]
A stretched film was obtained under the same conditions as in Example 2, except that dimethyl terephthalate was used instead of dimethyl ester naphthalene-2,6-dicarboxylic acid. The properties of the obtained film are shown in Table 1. In addition, it is thought that the measurement crystal plane in this comparative example originates from the (100) plane in the crystal lattice of polyethylene terephthalate, and the Bragg angle was about 26 °. Since the naphthalene-2,6-dicarboxylate component is not contained as a main constituent as defined in the present invention, the puncture resistance was not sufficient.

[Comparative Example 4]
A battery was prepared by the above method (10) using the metal foil shown in Table 1 as a positive and negative electrode current collector instead of the stretched film laminated with the metal film, and the same evaluation was performed. Since a polyester film as defined in the present invention was not used, the puncture resistance was not sufficient.

  The flame retardant polyester film for power storage element electrode of the present invention is a thin polyester film that enables higher volume and weight energy density than conventional products, but has high puncture resistance and bending resistance suitable for power storage element electrode applications. In addition, since it has flame retardancy, it is possible to provide a film suitable for an electrode for an electricity storage element, particularly for a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor.

1: Polyester film 2: Aluminum thin film 3: Positive electrode 4: Copper thin film 5: Negative electrode 6: Separator

Claims (16)

  A flame-retardant polyester film having at least one polyester layer A mainly composed of polyethylene naphthalene dicarboxylate, wherein the polyester layer A is derived from at least one of a carboxyphosphinic acid compound and a carboxyphosphinic acid compound Is equivalent to a diffraction peak having a Bragg angle of 25 ° to 29 ° obtained by wide-angle X-ray diffraction measurement in the polyester film. A flame retardant polyester film for a storage element electrode, wherein the coincidence of the crystal plane normal to the film plane normal is 0.95 or more and the film thickness is 0.2 μm or more and 30 μm or less. The flame-retardant polyester film for a storage element electrode according to claim 1, wherein the carboxyphosphinic acid compound is a compound represented by the following formula (I).

Wherein R ¹ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ² and R ³ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group or a hydrogen atom. X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{1 to} R ³ may be the same or different. The flame-retardant polyester film for a storage element electrode according to claim 1, wherein the carboxyphosphinic acid compound is a compound represented by the following formula (II).

(Wherein R ⁴ is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 18 carbon atoms, R ⁵ and R ⁶ are alkyl groups having 1 to 18 carbon atoms, an aryl group, a monohydroxyalkyl group, or a hydrogen atom) X represents a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ^{4 to} R ⁶ may be the same or different.   The flame-retardant polyester film has a laminated structure in which a polyester layer B is further laminated on at least one surface of the polyester layer A, the main component of the polyester layer B is polyethylene naphthalene dicarboxylate, and the carboxyphosphine in the layer B The content as a phosphorus atom of a component derived from at least one of an acid compound or a carboxyphosphinic acid compound is 0% by weight or more and 1% by weight or less based on the layer B and less than or equal to the phosphorus atom content of the layer A The flame-retardant polyester film for electrical storage element electrodes according to any one of claims 1 to 3.   The flame-retardant polyester film for a storage element electrode according to claim 4, wherein the polyester layer A and the polyester layer B have a laminated structure in which three or more layers are alternately laminated.   The flame retardant polyester film for a storage element electrode according to any one of claims 1 to 5, wherein a conductive thin film is formed on at least one surface of the flame retardant polyester film.   The flame retardant polyester film for a storage element electrode according to claim 6, wherein the conductive thin film is a metal thin film.   The flame-retardant polyester film for a storage element electrode according to claim 7, wherein the metal thin film contains an aluminum element as a main component.   The flame-retardant polyester film for a storage element electrode according to claim 7, wherein the metal thin film contains a copper element as a main component.   A metal thin film is formed on both sides of the flame retardant polyester film, the metal thin film formed on one side is mainly composed of aluminum element, and the metal thin film formed on the other side is mainly composed of copper element. The flame-retardant polyester film for a storage element electrode according to claim 7.   The electrode for electrical storage elements formed by laminating | stacking an electrode agent further on the surface of the electroconductive thin film of the flame-retardant polyester film for electrical storage element electrodes in any one of Claims 1-10.   The electrode for electrical storage elements whose main component of the electrode agent in the electrode for electrical storage elements of Claim 11 is lithium * transition metal complex oxide.   The electrode for electrical storage elements in which the main component of the electrode agent in the electrode for electrical storage elements of Claim 11 is carbon which has an amorphous carbon structure.   An electrode agent mainly composed of a lithium / transition metal composite oxide is laminated on a surface of a metal thin film mainly composed of an aluminum element of the flame retardant polyester film for a storage element electrode according to claim 10, and mainly composed of a copper element. An electrode for a storage element, in which an electrode agent mainly composed of carbon having an amorphous carbon structure is laminated on the surface of a metal thin film as a component.   The electrode for an electrical storage element according to claim 11, which is used for a lithium ion secondary battery or an electric double layer capacitor.   The electrical storage element formed by incorporating the electrode for electrical storage elements in any one of Claims 11-15.

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