JP2002299169A - Separator for electric double-layer capacitor and the electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an electric double-layer capacitor in which short-circuit is hard to be generated and internal resistance can be reduced, and to provide the electric double-layer capacitor which uses the separator. SOLUTION: The separator for an electric double-layer capacitor consists of a fiber sheet containing two or more fiber layers which contain synthetic fiber having fibril and a fiber whose fineness is at most 0.45 dtex. At least two layers from among the fiber layers are fiber layers of different apparent densities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for an electric double layer capacitor and an electric double layer capacitor.

[0002]

2. Description of the Related Art Electric double-layer capacitors (Electri)
c Double Layer Capacitor;
EDLC) has a relatively large capacity, and has a long life and is capable of rapid charge and discharge. Therefore, besides conventional uses such as power supply smoothing or noise absorption, a memory backup power supply for a personal computer, or In recent years, it has been used as a secondary battery for an electric vehicle. The electric double layer capacitor is a capacitor using an electric double layer generated at the interface between the polarizable electrode and the electrolyte. In other words, when a pair of electrodes is immersed in an ionic electrolyte and a voltage lower than the electrolysis voltage of the electrolyte is applied,
Ions of the opposite sign to the electrode are distributed very close to the electrode to form an ion layer. On the other hand, the electric charge of the opposite sign to that of the ion layer is accumulated inside the electrode. The ionic layer and the charge layer are called an electric double layer. The electric charge accumulated in the electric double layer is discharged when a load is connected between the positive and negative electrodes, and at the same time, ions are separated from the electrodes and the electrolyte returns to a neutralized state. Since the capacity of an electric double layer capacitor is determined by the surface area of the electrode, activated carbon with a large surface area is used for the electrode, and an ionic electrolytic solution is an organic type that is advantageous in terms of capacity, withstand voltage, energy density, etc. Things are used.

In such an electric double layer capacitor, if a pair of electrodes come into contact with each other, it becomes difficult to form an ionic layer and a charge layer at the interface between the electrode and the electrolyte. A separator having ion permeability and electrical insulation is arranged between the electrodes. As a conventional separator for an electric double layer capacitor, electrolytic paper comprising two or more fiber sheets formed by a papermaking net is known. However, in some cases, sufficient short-circuit prevention properties cannot be obtained with this electrolytic paper. In this case, if two or more electrolytic papers are used, the above problem can be reduced, but there is a problem that the internal resistance is increased.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a separator for an electric double layer capacitor which solves the above-mentioned disadvantages of the prior art, hardly causes a short circuit, and can reduce the internal resistance. And an electric double layer capacitor using the same.

[0005]

The object of the present invention is to provide a fibril-containing synthetic fiber and a fineness of 0.45 dt according to the present invention.
ex, and at least two of the fiber layers are fiber layers having different apparent densities from each other. The problem can be solved by using a separator. The present invention also relates to an electric double layer capacitor including the electric double layer capacitor separator.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A separator for an electric double layer capacitor (hereinafter sometimes simply referred to as a separator) of the present invention is a synthetic fiber having fibrils (hereinafter referred to as a fibril synthetic fiber) having a fineness of 0.45 dtex or less. And at least two of the fiber layers are fiber layers having different apparent densities. The mode of the fiber sheet is not particularly limited, but may be, for example, a woven fabric, a knitted fabric, a nonwoven fabric, or a composite thereof. Among these, a nonwoven fabric is preferable because the thickness can be reduced, and a wet nonwoven fabric is more preferable because it has excellent uniform dispersion of fibers, hardly causes short circuit, and has high reliability.

[0007] The fibril synthetic fiber used in preparing the separator of the present invention is composed of one fiber (that is, a stem fiber), and a part thereof is branched to form an infinite number of fine fibers (that is, a branched fiber). It is not particularly limited as long as it is a generated fiber, or a fiber in which an innumerable fine fiber is generated by dividing the whole, for example, fibril synthetic fiber composed of only fine fiber Alternatively, a fibril synthetic fiber including a fine fiber portion and a stem fiber portion can be used. In a fibril synthetic fiber including a fine fiber portion and a stem-like fiber portion, the fine fiber portion can be located at an end (one or both ends) and / or inside the fibril synthetic fiber.

[0008] The fibril synthetic fiber used in the separator of the present invention can be made of an arbitrary resin. It is preferable in manufacturing an electric double layer capacitor. The “melting temperature” in the present specification is a differential thermal analysis curve (DTA curve) obtained by a differential thermal analysis defined in JIS K7121.
Means the temperature obtained from In addition, the “carbonization temperature” in the present specification means a temperature obtained by thermogravimetry defined in JIS K 7120.

For example, in an electric double layer capacitor using an organic electrolyte, individual materials (for example,
If the collector electrode, the electrode, or the separator contains moisture, it is difficult to manufacture an electric double layer capacitor with a high withstand voltage or an electric double layer capacitor with a high energy density. It needs to be dry. However, a separator made of polypropylene fiber or a separator made of cellulose pulp, which has been conventionally used, has a lower heat-resistant temperature as compared with materials such as a collector and an electrode, and thus the collector, the electrode, and the separator were assembled. Subsequent drying at a temperature of 150 ° C. or more causes significant deterioration such as melting or carbonization of the separator, making it difficult to simultaneously dry these materials after assembling them. On the other hand, if the individual materials are separately dried and then assembled, the deterioration of the separator can be prevented, but there is a problem that it takes too much time. Therefore, as described above, the fibril synthetic fiber constituting the separator has a melting temperature or a carbonization temperature of 300.
The use of fibril synthetic fibers composed of a resin at a temperature of at least
Because it can be dried at a temperature of 50 ° C or more at the same time,
An electric double layer capacitor having a high withstand voltage and an electric double layer capacitor having a high energy density can be easily manufactured.

As a resin having a melting temperature of 300 ° C. or more,
For example, polytetrafluoroethylene or polyphenylene sulfide can be used. Examples of the resin having a carbonization temperature of 300 ° C. or higher include, for example, meta-based wholly aromatic polyamide, para-based wholly aromatic polyamide, polyamideimide, aromatic polyetheramide, polybenzimidazole, and wholly aromatic polyester. be able to. Among these, meta-based wholly aromatic polyamides or para-based wholly aromatic polyamides are also preferable because of their excellent affinity with the electrolytic solution, and in view of a high carbonization temperature, para-based wholly aromatic polyamides are preferred. More preferred.

The "fiber having a fineness of 0.45 dtex or less" used for preparing the separator of the present invention has a fineness of 0.15 dtex.
There is no particular limitation as long as the fiber is 45 dtex or less. In this specification, “fineness” refers to J
It means the value obtained by the method A defined in IS L 1015. Fineness 0 used in the separator of the present invention.
The fiber of 45 dtex or less can be made of any resin, but if the softening temperature is made of a resin having a temperature of 200 ° C or more, the fibril synthetic fiber is made of a resin having a melting temperature or a carbonization temperature of 300 ° C or more. For the same reason as described above, it is preferable in manufacturing an electric double layer capacitor. In the present specification, “softening temperature” refers to JIS
D obtained by heat flux differential scanning calorimetry (DSC, heating temperature = 10 ° C./min) specified in K 7121
It means the temperature that gives the starting point of the melting endothermic curve in the SC curve.

As the resin constituting the fiber having a fineness of 0.45 dtex or less, for example, a polyamide resin (for example,
66 nylon), polyester resin, acrylic resin, polyvinyl alcohol, and the like. Among these, polyester resins are preferred because they have excellent stability in an electrolytic solution and have a softening temperature of 200 ° C. or higher.

The fiber length of the fibers having a fineness of 0.45 dtex or less used in preparing the separator of the present invention is not particularly limited, and varies depending on the mode of the fiber sheet. For example, when the fiber sheet is made of a wet nonwoven fabric, the fiber length is preferably 1 to 25 mm, and 3 to 2 mm.
More preferably, it is 0 mm. The “fiber length” in the present invention means a length obtained by the method B (corrected staple diagram method) of JIS L 1015.
The cross-sectional shape of the fiber having a fineness of 0.45 dtex or less is
There is no particular limitation, for example, it can be circular or non-circular, for example, an ellipse, an ellipse,
It can also be star-shaped, various alphabetic character types (for example, Y-shaped or X-shaped, etc.), or a plus (+) type.

In the separator of the present invention, at least two of the plurality of fiber layers constituting the fiber sheet are fiber layers having different apparent densities. In this specification, the “apparent density” of the fiber layer means a value obtained by dividing the area density by the thickness [that is, (area density) / (thickness)]. In this specification, “area density” refers to JIS P 8124
(Paper and paperboard-Basis weight measurement method) means the basis weight based on the method defined in, and the "thickness" is a value measured by the method specified in JIS B7502, that is, measured by the outer micrometer under a 5N load. Mean measured value. In the separator of the present invention, as long as the apparent density of the fiber layer is different,
The difference in apparent density is not particularly limited.
It is preferably from ⁵ to 0.3 g / cm ³ .

In the separator of the present invention, the means for causing a difference in the apparent density of the fiber layer is not particularly limited. For example, by mixing fibers having different fiber diameters, A method of giving a difference in hanging density or a method of giving a difference in apparent density to the target fiber layer depending on a difference in pressure applied to the target fiber layer can be used, and further, a combination of these methods can be used.

In the separator of the present invention, it is preferable that the difference in the apparent density of the fiber layers is caused by mixing fibers having different fiber diameters. As such a separator of the present invention, for example, as a fiber having a fineness of 0.45 dtex or less, in a fiber layer having a high apparent density (hereinafter sometimes referred to as a dense fiber layer), a fiber having a relatively small fineness is used. In a fiber layer having a low apparent density (hereinafter, sometimes referred to as a crude fiber layer), the fibers used in the dense fiber layer (that is,
Separators using fibers having a relatively large fineness than fibers having a relatively small fineness can be given. In this case, the coarse fiber layer may further include the fibers used in the dense fiber layer (that is, fibers having relatively small fineness), or the dense fiber layer may further include the fibers used in the coarse fiber layer. Fiber (ie, relatively fine fiber)
Can also be included.

More specifically, for example, it consists essentially of (a) a fibril synthetic fiber and (b) a fine fiber having a fineness of 0.2 dtex or less (hereinafter sometimes simply referred to as "fine fiber"). At least one dense fiber layer, (a) a fibril synthetic fiber, (b) a fine fiber having a fineness of 0.2 dtex or less, and (c) a fineness exceeding 0.2 dtex.
A separator made of a fiber sheet including at least one coarse fiber layer substantially consisting of a thick fiber of 45 dtex or less (hereinafter sometimes simply referred to as “thick fiber”) can be given. Hereinafter, the separator of the present invention will be further described based on this specific embodiment. In the present specification, the phrase "a certain fiber layer is substantially composed of specific fibers" means that the fiber layer does not contain fibers other than the specific fibers in a substantial amount. For example, it means that the ratio of the specific fiber in the fiber layer is 95% or more.

The fine fibers capable of forming the dense fiber layer and the coarse fiber layer (that is, having a fineness of 0.2 dtex)
Except that the fineness is 0.2 dtex or less, the description given above regarding the “fiber having a fineness of 0.45 dtex or less”, that is, the type of the resin that can constitute the fiber, the fiber Each description regarding the length and the cross-sectional shape of the fiber is directly applicable. Also, the thick fiber (that is, a thick fiber having a fineness of more than 0.2 dtex and 0.45 dtex or less) that can constitute the coarse fiber layer has a fineness of more than 0.2 dtex and 0.45 dtex.
except that the fineness is 0.45 dt
The description given above for "fibers of ex or less" applies as it is.

That is, the fine fibers and the thick fibers are
Each of them can be made of any resin, but when the softening temperature is made of a resin having a temperature of 200 ° C. or more, the same reason as when the fibril synthetic fiber is made of a resin having a melting temperature or a carbonization temperature of 300 ° C. or more. Is preferable in manufacturing an electric double layer capacitor. Examples of the resin constituting the fine fiber and the thick fiber include a polyamide resin (for example, 66 nylon), a polyester resin, an acrylic resin, and polyvinyl alcohol. Among these, polyester resins are preferred because they have excellent stability in an electrolytic solution and have a softening temperature of 200 ° C. or higher. Further, the fiber length of the fine fiber and the thick fiber is not particularly limited, and varies depending on the mode of the fiber sheet. For example, when the fiber sheet is made of a wet nonwoven fabric, the fiber length is preferably 1 to 25 mm, and more preferably 3 to 20 mm. Furthermore, the cross-sectional shapes of the fine fibers and the thick fibers are not particularly limited, and may be, for example, circular, or
It can also be non-circular, for example, oval, elliptical, star-shaped, various alphabetic character-types (eg, Y-shaped or X-shaped, etc.), or plus (+)-shaped.

The dense fiber layer in the separator of the present invention comprises:
Substantially composed of fibril synthetic fibers and fine fibers of 0.2 dtex or less is preferable because entry of the electrode constituent substance can be prevented. In addition, the form can be maintained by mechanical entanglement with the fibril synthetic fibers, and the strength is excellent, so that a short circuit is less likely to occur. Moreover, when it is substantially composed of the fibril synthetic fiber and the fine fiber of 0.2 dtex or less, the state can be reduced in thickness, and the energy density per fixed volume can be easily increased. Furthermore,
When the fineness of the fine fibers is 0.2 dtex or less, the generation of pinholes can be further prevented.

The dense fiber layer in the separator of the present invention comprises:
When substantially composed of fibril synthetic fibers and fine fibers of 0.2 dtex or less, the ratio of fibril synthetic fibers to fine fibers is not particularly limited, but may be 35: 6.
The ratio is preferably 5 to 90:10. The apparent density of the dense fiber layer is not particularly limited, but may be 0.6%.
It is preferably from 0.9 g / m ³ to 0.9 g / m ³ . Further, the surface density of the dense fiber layer is not particularly limited, but 10 g
/ M ² or more.

The dense fiber layer in the separator of the present invention comprises:
When substantially composed of a fibril synthetic fiber and a fine fiber of 0.2 dtex or less, the fibril synthetic fiber may include only one kind of fibril synthetic fiber, or may differ in terms of fiber diameter and / or resin composition. Two or more types can be included. Further, in the dense fiber layer, 0.2 d
It can also contain only one kind of fine fiber of tex or less,
Alternatively, two or more types of fine fibers differing in fiber diameter and / or resin composition may be included.

On the other hand, the crude fiber layer in the separator of the present invention comprises fibril synthetic fiber, fine fiber of 0.2 dtex or less, 0.2 dtex and 0.45 dtex.
When substantially composed of the following thick fibers, the fineness of the thick fibers exceeds 0.2 dtex and is 0.45 dtex or less, so that the internal resistance can be reduced without generating pinholes.

The crude fiber layer in the separator of the present invention comprises:
When the fibril synthetic fiber, a fine fiber of 0.2 dtex or less, and a thick fiber exceeding 0.2 dtex and substantially 0.45 dtex or less, the proportion of the thick fiber contained in the crude fiber layer is: The ratio is not particularly limited as long as the ratio can prevent the short circuit, but is 5 to 40% by mass of all the fibers constituting the crude fiber layer (that is, fibril synthetic fibers, fine fibers, and thick fibers). Is preferred. The ratio of the fibril synthetic fibers contained in the crude fiber layer is not particularly limited, but is preferably 35 to 70 mass% of all the fibers constituting the crude fiber layer. Furthermore, the proportion of fine fibers contained in the crude fiber layer is
Although not particularly limited, the content is preferably 25 to 60 mass% of all fibers constituting the crude fiber layer. The apparent density of the crude fiber layer is not particularly limited,
It is preferably 0.55~0.7g / m ^3. The difference between the apparent density of the dense fiber layer and the apparent density of the coarse fiber layer is not particularly limited, but may be 0.05 to 0.3.
g / m ³ . Furthermore, the areal density of the crude fiber layer in the separator of the present invention is not particularly limited, but is preferably 10 g / m ² or more.

The crude fiber layer in the separator of the present invention comprises:
In the case of substantially consisting of fibril synthetic fibers, fine fibers of 0.2 dtex or less, and thick fibers of more than 0.2 dtex and 0.45 dtex or less, only one type of fibril synthetic fibers may be included. Alternatively, two or more types of fibril synthetic fibers differing in fiber diameter and / or resin composition may be included. The crude fiber layer may include only one type of fine fiber having a size of 0.2 dtex or less, or may include two or more types of fine fiber having different fiber diameters and / or resin configurations. Furthermore,
In the crude fiber layer, it exceeds 0.2 dtex and 0.4
Only one type of thick fiber of 5 dtex or less may be included, or two or more types of thick fiber differing in fiber diameter and / or resin composition may be included.

[0026] In the separator of the present invention, it is preferable that the fibers constituting each of the fiber layers are in a state of being pressed together. In the present specification, the term "compression bonding" means that the fibers are brought into close contact with each other by applying pressure in a state where the fibers are not heated or in a state where all the constituent fibers are heated below the softening temperature. The temperature at which all the fibers of the constituent fibers do not soften is one temperature lower than the softening temperature of the resin having the lowest softening temperature among the resins forming the constituent fibers.
The temperature is preferably 0 ° C. or lower, more preferably 20 ° C. or lower. In addition, the pressure applied in the pressure treatment is not particularly limited, but as the fibers are pressure-bonded with each other, the strength can be maintained.
The linear pressure is preferably 50 N / cm or more. When the separator of the present invention is in a state where the respective fibers constituting the respective fiber layers are pressure-bonded to each other, the separator can be in a state of high strength, and thus can be in a state of small thickness. Further, unlike in the case where the fibers are fused together, the film is not formed into a film and does not hinder the ion permeability. Further, the internal resistance is low, and the energy density per fixed volume can be increased.

The number of dense fiber layers and coarse fiber layers is not particularly limited as long as the separator of the present invention includes at least one dense fiber layer and at least one coarse fiber layer.
The order of arranging the dense fiber layer and the coarse fiber layer in the separator of the present invention is not particularly limited. However, when manufacturing an electric double layer capacitor in which two separators of the present invention are arranged in a stacked state. The arrangement order of the dense fiber layer and the coarse fiber layer in each separator is such that the apparent density increases stepwise from one surface fiber layer to the other surface fiber layer, or in a stepwise manner. It is preferable to arrange them so as to reduce the number.

The areal density of the separator of the present invention is not particularly limited, but is preferably, for example, 20 to 40 g / m ² . Further, the thickness of the separator of the present invention is not particularly limited.
It is preferably 0 μm. Furthermore, the apparent density of the separator of the present invention is not particularly limited, but is preferably, for example, 0.5 to 0.8 g / cm ³ .
When the areal density, thickness, and apparent density are within the above-mentioned preferred ranges, a separator having excellent strength, high energy density per fixed volume, and low internal resistance can be obtained.

The electric double layer capacitor of the present invention includes the separator for an electric double layer capacitor of the present invention, and preferably includes two or more of the separators. By using two or more separators, the short circuit can be more reliably prevented. The electric double layer capacitor of the present invention can have the same configuration as a conventionally known electric double layer capacitor except that the separator of the present invention is included as a separator. For example, the electric double layer capacitor of the present invention can be configured by disposing the separator of the present invention between a pair of electrodes. More specifically,
For example, as shown in Examples described later, each is a sheet-like collector electrode (for example, an aluminum thin plate), an electrode (for example, an electrode obtained by mixing and kneading granular activated carbon, carbon black, and polytetrafluoroethylene), a separator, Forming an electric double layer capacitor of the present invention by stacking an insulating sheet on the uppermost layer and / or the lowermost layer in which the electrode and the collecting electrode are stacked in this order, and then processing this electrode group into a wound shape. Can be.

In the electric double layer capacitor of the present invention, the method of arranging the separator and the electrode is not particularly limited, but it is preferable that the dense fiber layer of the separator is in contact with the electrode.
It is preferable to arrange a separator and an electrode. With such an arrangement, entry of the electrode constituent material can be reliably prevented, and the crude fiber layer can contribute to lowering the internal resistance.

The method for producing the separator of the present invention is not particularly limited. For example, a method of producing a fiber sheet having a difference in density by a conventional method, and laminating and integrating the fiber sheet to use as a separator. Thereby, the separator of the present invention can be manufactured. For example, a suitable wet nonwoven fabric including a dense fiber layer and a coarse fiber layer can be manufactured as follows. First, fibril synthetic fiber,
A fine fiber of 0.2 dtex or less and a thick fiber of more than 0.2 dtex and 0.45 dtex or less are prepared. Since these fibril synthetic fibers, fine fibers, and thick fibers are all commercially available, they can be easily obtained. Then, using a fibril synthetic fiber and a fine fiber, a conventional wet method (for example, a horizontal long net system, an inclined wire short net system, a circular net system, a short net / circular net combination system, or a long net / circle) A wet fiber web for a dense fiber layer is formed by a net combination method or the like. On the other hand, using a fibril synthetic fiber, a fine fiber, and a thick fiber, an ordinary wet method (for example, a horizontal long net system, a slanted wire short net system, a circular net system, a short net / circular net combination system, or A wet fiber web for a crude fiber layer is formed by a long net / circular net combination method. When forming each of these fiber webs, a thickener is added to maintain a uniform dispersion state of the fibers, a surfactant is added to increase the affinity between water and the fibers, or agitation is caused by stirring or the like. An antifoam can be added to remove air bubbles.

Next, these wet fiber webs are laminated and then dried in a wet state, or separately dried for each individual web to remove moisture, and laminated to obtain a dry and wet nonwoven fabric. be able to.
The drying is performed at a temperature at which the fibers constituting the fiber web do not melt. The fibers can be pressed against each other by applying pressure to the obtained dry wet nonwoven fabric using a calender or the like, if desired.
By applying pressure in this way, for example, to adjust the thickness, to reduce the thickness, to equalize the thickness,
The fibrillation of the fibril synthetic fibers can be advanced to make them more dense, or the fine fibers of the fibril synthetic fibers can be brought into close contact with each other to improve the strength. In addition, when applying pressure, it can be carried out in a heated state or in a non-heated state, but when heated, the above-mentioned thickness adjusting effect and strength improving effect are easily exerted. However, when heated to such an extent that the constituent fibers are melted, a film is formed and ion permeability deteriorates. Therefore, when heating, the resin having the lowest softening temperature of the resin having the lowest softening temperature among the constituent resins of the constituent fibers is heated. Also one
The heating is preferably performed at a temperature lower than 0 ° C, more preferably at a temperature lower than 20 ° C.

[0033]

EXAMPLES The present invention will be described below in more detail with reference to examples, but these examples do not limit the scope of the present invention.

Example 1 Fibril synthetic fibers made of para-based wholly aromatic polyamide [Kevlar (registered trademark); manufactured by Dupont, carbonization temperature = 500 ° C. or more], and fine fibers made of polyethylene terephthalate (fineness = 0.11 dtex, fiber length) =
3 mm, melting temperature = 260 ° C., softening temperature = 253 ° C., cross section = circular) and thick fiber made of polyethylene terephthalate (fineness = 0.3 dtex, fiber length = 3 mm, melting temperature = 260 ° C., softening temperature = 253 ° C.) (Cross section = circular). The fibril synthetic fiber and the fine fiber,
A first slurry mixed at a mass ratio of 50:50, the fibril synthetic fiber, the fine fiber, and the thick fiber,
A second slurry mixed at a mass ratio of 50:10:40 was prepared. Next, in a paper machine equipped with a slanted wire type short net, a downstream net, and a Yankee dryer, the first slurry is sent to the short net, the second slurry is sent to the round net, and each wet sheet is fed. To form a wet sheet, and then the laminated wet sheet was dried using a Yankee dryer set at a temperature of 120 ° C. The obtained dried sheet is heated at a temperature of 220.
C. (a linear pressure = 500 N / cm) by a pair of heat calenders set to a wet nonwoven fabric, that is, the separator of the present invention (area density = 30 g / m ² , thickness = 43 μm).
m, apparent density = 0.7 g / cm ³ ). The fibril synthetic fiber constituting the separator was a fiber including a fine fiber portion and a stem fiber portion. Further, although the fine fiber and the thick fiber were somewhat compressed, they were not heat-sealed, so that no film was formed. In this separator, the fiber layer derived from the first slurry had a dense surface (area density = 15 g / m ² , apparent density = 0.83 g / c).
m ³ ), and the fiber layer derived from the second slurry has a rough surface (area density = 15 g / m ² , apparent density = 0.6 g / cm ³ )
Was composed.

[0034]

Embodiment 2 In a paper machine equipped with both a first combination of a slanted wire net and a Yankee dryer and a second combination of a downstream mesh and a Yankee dryer, a first slurry similar to that of the first embodiment is used. Was supplied to the inclined wire-type short net, and the same second slurry as in Example 1 was supplied to the downstream circular net to form wet sheets. Each of these wet sheets was dried by a Yankee dryer set at a temperature of 120 ° C. Each of the obtained dried sheets has a surface density of 15 g for both the short net and the circular net.
/ M ² . The dried short netting sheet and the dried circular netting sheet are overlapped and pressed by a pair of heat calenders set at a temperature of 220 ° C. (linear pressure = 500 N / c).
m) to obtain a wet nonwoven fabric, that is, the separator of the present invention (area density = 30 g / m ² , thickness = 43 μm, apparent density =
0.7 g / cm ³ ). The fibril synthetic fiber constituting this separator was a fiber containing a fine fiber portion and a stem fiber portion. In addition, fine fibers and thick fibers are
Although the film was somewhat pressed, no film was formed because it was not thermally fused. Also, this separator
The fiber layer derived from the first slurry has a dense surface (area density = 15 g).
/ M ² , apparent density = 0.83 g / cm ³ )
The fiber layer derived from the slurry has a rough surface (area density = 15 g / m
² , apparent density = 0.6 g / cm ³ ).

[0035]

Example 3 A slurry in which fibril synthetic fibers, fine fibers and thick fibers were mixed at a mass ratio of 50:40:10 was used as a second slurry, and two forward-flow circular nets were used as a paper machine. A wet-type nonwoven fabric, that is, a separator of the present invention (area density = 30 g / m ² , thickness = 43 μm, Apparent density = 0.7 g / cm ³ ). The fibril synthetic fiber constituting this separator was a fiber containing a fine fiber portion and a stem fiber portion. Further, although the fine fibers and the thick fibers were somewhat compressed, they were not heat-sealed, and thus no film was formed. In this separator, the fiber layer derived from the first slurry has a dense surface (area density =
15 g / m ² , apparent density = 0.75 g / cm ³ ), and the fiber layer derived from the second slurry has a rough surface (area density = 1).
5 g / m ² , apparent density = 0.65 g / cm ³ ).

[0036]

Embodiment 4 The same first slurry as in Embodiment 1 was supplied to a paper machine provided with a slanted wire type short net and a Yankee dryer to form a wet sheet, and the wet sheet was heated to 120 ° C. And dried with a Yankee dryer set to Separately, a wet sheet is formed by supplying the same second slurry as in Example 1 to a paper machine equipped with a slanted wire-type short net and a Yankee dryer. It was dried with a Yankee dryer set at 120 ° C. Each of the obtained dried sheets was a sheet having an areal density of 15 g / m ² . Two of these dry sheets are stacked and the temperature is 220 ° C.
Pressed by a pair of thermal calendars set to
500 N / cm) to obtain a wet nonwoven fabric, that is, the separator of the present invention (area density = 30 g / m ² , thickness = 43 μm).
m, apparent density = 0.7 g / cm ³ ). The fibril synthetic fiber constituting this separator was a fiber containing a fine fiber portion and a stem fiber portion. Further, although the fine fibers and the thick fibers were somewhat compressed, they were not heat-sealed, and thus no film was formed. In this separator, the fiber layer derived from the first slurry had a dense surface (area density = 15 g / m ² , apparent density = 0.81 g / c).
m ³ ), and the fiber layer derived from the second slurry has a rough surface (area density = 15 g / m ² , apparent density = 0.61 g / c).
m ³ ).

[0037]

Comparative Example 1 The same first slurry as in Example 1 was supplied to a paper machine equipped with two forward-flow circular nets and a Yankee dryer, and a laminated wet sheet in which the respective wet sheets of each circular net were laminated. Was formed. The laminated wet sheet is heated at a temperature of 12
It was dried with a Yankee dryer set at 0 ° C. The obtained dried sheet is pressed (linear pressure = 500 N / cm) by a pair of heat calenders set at a temperature of 220 ° C. to obtain a wet nonwoven fabric, that is, a comparative separator (area density = 30 g / m ² , thickness). = 43μm, apparent density = 0.7g
/ Cm ³ ). The fibril synthetic fiber constituting this separator was a fiber containing a fine fiber portion and a stem fiber portion. Further, although the fine fibers constituting the separator were somewhat pressure-bonded, they were not heat-sealed, and thus no film was formed. Further, this separator had a single-layer structure with no apparent density difference.

[0038]

[Evaluation of physical properties] (1) Production of capacitor A thin aluminum plate was prepared as a collecting electrode. In addition, an electrode (made by a rolling method) prepared by mixing and kneading granular activated carbon, carbon black, and polytetrafluoroethylene was prepared. Further, as a separator, in addition to the separator of the present invention manufactured in Examples 1 to 4 and the comparative separator manufactured in Comparative Example 1, a commercially available cellulose separator for capacitors (Comparative Example 2; areal density = 20 g / m ² , thickness = 48 μm, apparent density = 0.4
g / cm ³ ). The collector, electrode, and separator were dried at 100 ° C. for 5 hours, 180 ° C. for 5 hours, and 100 ° C. for 5 hours, respectively. Next, the collector sheet, the electrode, two separators, the electrode, and the insulating sheet were stacked on the lowermost layer stacked with the collector electrode in the glow box, and then this electrode group was processed into a wound shape with a load of 500 g.
A solution obtained by dissolving tetraethylammonium / tetrafluoroborate in propylene carbonate as an electrolytic solution was impregnated under reduced pressure, and then sealed to produce four types of capacitors of the present invention and two types of comparative capacitors. Regarding the separators of the present invention manufactured in Examples 1 to 4, the dense layers of the two separators were respectively arranged outside and inserted so as to be in contact with the electrodes on both sides.

(2) Performance Evaluation of Capacitor The following measurements were obtained from charge / discharge curves measured by a charge / discharge tester under the following charge / discharge conditions. That is,
The internal resistance was determined from a charge / discharge curve obtained by an operation of charging to 2.5 V for 2 minutes at a constant current of 1 A and discharging for 2 minutes. The capacitance is 1 at a constant current of 0.02 A.
It was obtained from a charge / discharge curve obtained by an operation of charging to 2.5 V for 0 minute and discharging for 10 minutes. The leakage current is calculated based on the amount of voltage drop of the capacitor applied to 0.9 V after 72 hours based on the following equation (1): i = C × (dV / dt) (1) Means current, C means capacitance, dV means voltage drop, and dt means time]. Table 1 shows the results.

<< Table 1 >> Separator Capacitance Internal resistance Leakage current number used (F) (Ω) (mA) Example 1 2 820 0.040 0.13 Example 2 2 822 0.041 0.12 Example 3 2 817 0.039 0.15 Example 4 2 820 0.048 0.17 Comparative Example 1 798 0.028 0.45 Comparative Example 2 4 685 0.037 0.10

As is clear from Table 1, the separator of the present invention exhibited a value comparable to that of the conventional cellulose separator (Comparative Example 2) with respect to the internal resistance. Further, when the number of sheets used in the conventional cellulose separator is three or less, it cannot be manufactured stably due to the occurrence of partial breakage or the like during winding. For this reason, the volume occupied by the separator increases, so that the electrode material in the volume of the capacitor decreases, and the capacitance decreases. As is clear from the comparison with Comparative Example 1, the separator of the present invention hardly caused a micro short circuit and was excellent in electrical insulation. The separator of the present invention is thin and has an effect of preventing short circuit by loading two sheets in the above arrangement,
Internal resistance is also reduced. As a result, the energy density can be improved, and the separator is most suitable for producing an electric double layer capacitor.

[0042]

According to the separator of the present invention, since the separator has the dense fiber layer, the intrusion of the electrode constituent substance can be prevented, and since the separator has the crude fiber layer, the internal resistance can be reduced. Further, since at least two layers including at least one dense fiber layer and at least one coarse fiber layer are provided, pinholes can be prevented from occurring, and short circuits can be prevented.

Claims (7)

[Claims] 1. A fiber sheet comprising two or more fiber layers containing synthetic fibers having fibrils and fibers having a fineness of 0.45 dtex or less, wherein at least two of the fiber layers have an apparent density of one another. A separator for an electric double layer capacitor, which is a different fiber layer. 2. The electric double layer capacitor separator according to claim 1, wherein the difference in the apparent density of the fiber layers is caused by blending fibers having different fiber diameters. 3. The fiber layer having a high apparent density is a dense fiber layer substantially composed of synthetic fibers having fibrils and fine fibers having a fineness of 0.2 dtex or less, and a fiber having a low apparent density. The layer is a synthetic fiber having fibrils, a fine fiber having a fineness of 0.2 dtex or less, and a fineness of 0.2 dte.
3. The separator for an electric double layer capacitor according to claim 1, wherein the separator is a crude fiber layer substantially consisting of thick fibers exceeding x and not more than 0.45 dtex. 4. 4. The separator for an electric double layer capacitor according to claim 1, wherein fibers constituting each fiber layer are pressure-bonded. 5. An electric double layer capacitor comprising the separator for an electric double layer capacitor according to claim 1. 6. The electric double layer capacitor according to claim 5, wherein two or more electric double layer capacitor separators are arranged between the pair of electrodes. 7. The electric double layer capacitor according to claim 6, wherein each of the contact surfaces with the electrodes is a fiber layer having a high apparent density.