JP2003045752A - Electric double-layer capacitor separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor separator which will not break, even a high pressure is applied for adhesion with an electrode, is superior in ion permeability and is superior in ionic solution retaining property. SOLUTION: The electric double-layer capacitor has a fiber layer comprising an ultra-fine fiber of fiber diameter of 4 μm or less and a thick fiber of fiber diameter of 7 μm or more.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a separator for electric double layer capacitors.

[0002]

2. Description of the Related Art Electric double layer capacitors have a relatively large capacity, and since they have a long life and can be rapidly charged and discharged, they are used for memory of personal computers in addition to conventional applications such as smoothing of power supply and noise absorption. It has been used as a backup power source or an auxiliary or substitute for a secondary battery, and in recent years, it is expected to be used as a secondary battery for an electric vehicle.

This electric double layer capacitor has a structure in which a pair of electrodes is immersed in an ionic solution. When a voltage is applied to the electric double layer capacitor, the ions having the opposite sign to the electrodes are distributed in the vicinity of the electrodes to form a layer of ions, while the charges having the opposite sign to the ions are accumulated inside the electrodes. Next, when a load is connected between the electrodes, the electric charges in the electrodes are discharged and, at the same time, the ions distributed in the vicinity of the electrodes are separated from the vicinity of the electrodes and returned to the neutralized state.

In such an electric double layer capacitor, when a pair of electrodes come into contact with each other, it becomes difficult to form an ion layer in the vicinity of the electrodes. Therefore, a separator is usually arranged between the pair of electrodes. . If this separator is not in close contact with the electrode, a portion with a small amount of ionic solution will be formed between the separator and the electrode, and the ion permeability will deteriorate, so in order to avoid such a state, the separator and the electrode Generally, a high pressure is applied so that the and are closely attached.

Conventionally, as this separator, a non-woven fabric obtained by a melt blow method and subjected to a plasma treatment is known. However, when a high pressure is applied to this separator, the separator is torn and the electrodes come into contact with each other, the ion permeability deteriorates, or the retention of the ionic solution is poor, so There is a problem that the ionic solution is easily absorbed and the life of the capacitor is shortened.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and does not break even when a high pressure is applied to bring it into close contact with an electrode, and the ion does not break. It is an object of the present invention to provide a separator for an electric double layer capacitor, which has excellent permeability and excellent retention of an ionic solution.

[0007]

A separator for an electric double layer capacitor (hereinafter, simply referred to as "separator") of the present invention comprises ultrafine fibers having a fiber diameter of 4 μm or less and a fiber diameter of 7
It is provided with a fiber layer containing thick fibers of μm or more. Therefore, even if a high pressure is applied, it is possible to prevent breakage of the separator due to the presence of the thick fibers, and even if a high pressure is applied, it is possible to secure some voids due to the presence of the thick fibers, Since it contains the ultrafine fibers, it is excellent in the retention of the ionic solution, and thus is a separator capable of manufacturing a capacitor having excellent ion permeability and a long life.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The fiber layer constituting the separator of the present invention contains ultrafine fibers having a fiber diameter of 4 μm or less so as to have excellent ionic solution retention and to prolong the life of the capacitor. Since the thinner the fiber diameter is, the better the retention of the ionic solution is, the fiber diameter is preferably 3 μm or less, more preferably 2 μm or less. Although the lower limit of the fiber diameter of the ultrafine fibers is not particularly limited,
About 0.01 μm is suitable.

The "fiber diameter" in the present invention means the diameter of a fiber when the cross-sectional shape of the fiber is circular, and the circle having the same cross-sectional area when the cross-sectional shape of the fiber is non-circular. The diameter of is considered to be the fiber diameter.

It is preferable that the fiber diameters of the ultrafine fibers are substantially the same so that a fiber layer having a uniform pore size is formed by the ultrafine fibers and the distribution of the ionic solution is uniform. That is, the standard deviation value (σ) of the fiber diameter distribution of the ultrafine fibers divided by the average fiber diameter (d) of the ultrafine fibers (=
It is preferable that σ / d) is 0.2 or less (preferably 0.18 or less). When the fiber diameters of the ultrafine fibers are exactly the same, the standard deviation value (σ) becomes 0,
The lower limit of the value (σ / d) is 0.

The "average fiber diameter (d) of the ultrafine fibers" is
An electron micrograph of the fiber layer of the separator is taken, the fiber diameters of 100 or more (n) ultrafine fibers in this electron micrograph are measured, and the measured fiber diameters are averaged. The “standard deviation value (σ)” of the ultrafine fibers refers to a value calculated from the following equation using the measured fiber diameter (χ). Standard deviation = {(nΣχ ² − (Σχ) ² ) / n (n−1)}
^1/2 Here, n means the number of ultrafine fibers measured, and χ means the fiber diameter of each ultrafine fiber.

The ultrafine fibers having a fiber diameter of 4 μm or less are
In the case of consisting of two or more groups from the viewpoint of fiber diameter distribution,
The above relationship is preferably established for each ultrafine fiber group.

Further, in order to form a fiber layer having a uniform pore size, each ultrafine fiber is
It is preferred that the diameters be substantially unchanged (ie have substantially the same diameter).

Such ultrafine fibers in which the diameters of the respective ultrafine fibers are substantially the same, or the ultrafine fibers in which the diameter does not substantially change in the fiber axis direction, are, for example, spinneret regulated in the sea component in the spinneret. Then, it can be obtained by removing the sea component of the sea-island type composite fiber obtained by the composite spinning method in which the island component is extruded and composited.

The sea component of the sea-island type composite fiber obtained by mixing the resin constituting the island component and the resin constituting the sea component, which is generally referred to as a mixed spinning method, and then spinning is removed. Is an ultrafine fiber in which the fiber diameters of the respective ultrafine fibers are substantially the same, or in the fiber axis direction,
Although it is difficult to obtain ultrafine fibers whose diameter does not change substantially, they can be used in the present invention.

It is also difficult to obtain ultrafine fibers in which the diameters of the respective ultrafine fibers are substantially the same, or ultrafine fibers in which the diameter does not substantially change in the fiber axis direction, by the melt blow method. It can be used in the invention.

Further, the ultrafine fibers generated by applying a mechanical action to the splittable fibers which can be split by a mechanical action (for example, a fluid flow such as a water flow, a calender, etc.) are If they are completely divided, it is possible to obtain ultrafine fibers in which the diameters of the ultrafine fibers are substantially the same, or ultrafine fibers in which the diameter does not change substantially in the fiber axis direction. However, in reality, splittable fibers are rarely completely split, and it is common for some splittable fibers to be split, so in reality, the fiber diameters of the ultrafine fibers are It is difficult to obtain ultrafine fibers having substantially the same value, or ultrafine fibers whose diameter does not change substantially in the fiber axis direction. In addition, even ultrafine fibers generated from the splittable fibers can be used in the present invention.

The ultrafine fibers of the present invention need only contain at least one type of the ultrafine fibers described above, and need not be one type. For example, a mechanical action is applied to ultrafine fibers formed from sea-island type composite fibers obtained by the composite spinning method, ultrafine fibers formed from sea-island type composite fibers obtained by the mixing spinning method, and / or splittable fibers. It can contain ultrafine fibers generated by

The ultrafine fibers may be composed of an organic component and / or an inorganic component, but it is preferably composed of an organic component capable of reducing the weight of the capacitor. More specifically, it may be composed of one or more kinds of resins such as polyamide resins and polyolefin resins. In particular, it is preferably composed of a polyolefin resin so as not to be attacked by an ionic solution. For example, polyethylene resin (for example, ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer, etc.), polypropylene resin (for example, polypropylene, propylene copolymer) Union), polymethylpentene resin (for example,
(Polymethylpentene, methylpentene copolymer, etc.), and is preferably made of polypropylene resin or polyethylene resin.

When the ultrafine fibers contain a resin component capable of being involved in fusion (hereinafter sometimes referred to as "fusion component"), and when the fusion components are fused, the ultrafine fibers are surely fixed. This is a preferred embodiment because the ultrafine fibers do not fall off and do not fluff.

When the ultrafine fibers are fused, the ultrafine fibers may be composed of only the fusion component, or the fusion component and a component having a melting point higher than that of the fusion component (hereinafter referred to as “non-fusion component”). It may be referred to as an "adhesive component"). When the ultrafine fiber is composed of two or more kinds of components including a fusion component and a non-fusion component like the latter, the fiber morphology is maintained and the ionic solution is retained even if the fusion component is fused. It is suitable because it has excellent properties.

When the ultrafine fibers are composed of a fusible component and a non-fusible component, it is preferable that the fusible component occupies a part or the whole of the surface of the ultrafine fiber so that they can be fused. More specifically, the cross-sectional shape of the ultrafine fibers is preferably, for example, a core-sheath type, an eccentric type, or a sea-island type. The non-fusing component preferably has a melting point higher than the melting point of the fusing component by 10 ° C. or more so that the fiber shape can be maintained.
More preferably, it has a high melting point.

The ultrafine fibers containing the fusible component and the non-fusible component are used as a die for pushing out the island component when the sea-island type composite fiber is spun by a conventional composite spinning method, and have the above-mentioned cross-sectional shape. (For example, a core-sheath type, an eccentric type, a sea-island type) is used to spin the sea-island type composite fiber to remove sea components, or the sea-island type composite fiber is spun by a conventional composite spinning method. At this time, the resin obtained by mixing the fusion component and the non-fusion component is supplied to the die for extruding the island component, the sea-island type composite fiber is spun, and the sea component is removed.

The "melting point" in the present invention means the temperature which gives the maximum value of the melting endothermic curve obtained by raising the temperature from room temperature using a differential scanning calorimeter at a temperature raising temperature of 10 ° C./min. In addition,
When there are two or more maximum values, the highest temperature maximum value is taken as the melting point.

It is preferable that the ultrafine fibers are short fibers having a high degree of freedom (fiber length is 30 mm or less) so that the ultrafine fibers are easily dispersed, but the ultrafine fibers, the sea-island type composite fibers, or the splittable fibers are cut. At this time, if the ultrafine fibers or the ultrafine fiber-forming resin component (for example, the island component of the sea-island composite fiber) are pressure-bonded to each other, the state becomes the same as that of the fibrillated fiber, and the ion permeability tends to deteriorate. Therefore, it is preferable to use ultrafine fibers, sea-island composite fibers, or splittable fibers in which it is difficult for the ultrafine fibers or the ultrafine fiber-forming resin components to be pressure bonded together during cutting.

Examples of such ultrafine fibers, sea-island type composite fibers, or splittable fibers that are difficult to press-bond include ultrafine fibers, sea-island type composite fibers, or splittable fibers containing polymethylpentene, or having a melting point of 166. It is preferable to use ultrafine fibers, sea-island type composite fibers, or splittable fibers containing polypropylene at a temperature of ℃ or higher (preferably 168 ℃ or higher).

Further, the cross-sectional shape of the ultrafine fibers is preferably circular so that the formation of the fiber layer becomes uniform and the distribution of the ionic solution is uniform.

Such an ultrafine fiber has a length of 5 m in the fiber layer of the separator so as to have excellent retention of the ionic solution.
It is preferable that the content of ass% is 10% or more.
%, More preferably 20% by mass
It is more preferable that the above is included. On the other hand, it is preferably 40 mass% or less, more preferably 35 mass% or less, and further preferably 30 mass% or less, in view of the relationship with the thick fibers as described below.

Since the separator of the present invention contains a thick fiber having a fiber diameter of 7 μm or more in addition to the ultrafine fiber as described above, the thick fiber can prevent the separator from breaking, and the thick fiber can be prevented. Protects against pressure and secures voids, and, in combination with the action of the ultrafine fibers as described above, has excellent ion permeability and ionic solution retention.

Since the thicker the fiber diameter, the more excellent the effect is, the fiber diameter is preferably 8 μm or more, more preferably 9 μm or more, further preferably 12 μm or more. . Incidentally, if the fiber diameter of the thick fiber is too large, the thickness of the separator becomes thicker, which tends to deteriorate the ion permeability,
It is preferably 35 μm or less, and more preferably 30 μm or less.

When the average fiber diameter of the thick fibers is 5 times or more the average fiber diameter of the ultrafine fibers, the thick fibers secure the voids, and the ultrafine fibers are likely to exist in the voids. In other words, the ultrafine fibers are present between the skeletons of thick fibers, and even if pressure is applied, the fibers are unlikely to break, and voids through which ions can pass can be secured, and moreover, an ionic solution can be retained. It is preferable because it is possible. More preferably, the average fiber diameter of the thick fibers is 5.5 times or more the average fiber diameter of the ultrafine fibers.

The average fiber diameter of the thick fibers is a value obtained in the same manner as the average fiber diameter of the ultrafine fibers. That is, it means a value obtained by taking an electron micrograph of the fiber layer of the separator, measuring the fiber diameters of 100 or more (n) thick fibers in the electron micrograph, and averaging the measured fiber diameters.

As such a thick fiber, Young's modulus is 50.
It is preferable to contain thick fibers having high elasticity of cn / dtex or more. This is because the high elastic thick fibers having such a Young's modulus are included, so that the fibers are less likely to be broken by the pressure, and moreover, the voids are easily resisted against the pressure. Since the higher Young's modulus is, the more excellent such an effect is, it is preferably 65 cn / dtex or more, and more preferably 80 cn / dtex or more.

This "Young's modulus" is defined in JIS L 101
5: 1999, the apparent Young's modulus value calculated from the initial tensile resistance measured by the method specified in paragraph 8.11. The initial tensile resistance is a value measured by a constant speed tension type tester.

The fiber diameter of the high-elasticity thick fiber is not particularly limited as long as it is 7 μm or more, but it is preferably 10 μm or more so that it is difficult to break and a void can be secured, and the thickness of the separator. Is preferably 35 μm or less so that it does not become too thick and impair ion permeability. The more preferable fiber diameter of the high elastic thick fiber is 13 to
30 μm, more preferably 13 to 25 μm
Is.

This high-elasticity thick fiber is excellent in the performance of preventing breakage of the separator and ensuring the voids. However, in order to maximize this performance, the average fiber diameter of the high-elasticity thick fiber is the average of the ultrafine fibers. It is preferably 6 times or more of the fiber diameter,
It is more preferably 6.5 times or more.

The average fiber length of the highly elastic thick fibers is preferably 2.5 times or more the average fiber length of the ultrafine fibers. By satisfying such a relationship, it is likely that ultrafine fibers are present between the skeletons made of highly elastic thick fibers. More preferably, the average fiber length of the highly elastic thick fibers is at least 3 times the average fiber length of the ultrafine fibers, and even more preferably 4
It is at least twice, and most preferably at least five times.

The "fiber length" in the present invention means JI.
SL 1015 (Chemical fiber staple test method) The length obtained by the B method (corrected staple diagram method), and the "average fiber length" is the average value of the fiber length of 100 randomly selected fibers.

The high-elasticity thick fiber may be composed of an organic component and / or an inorganic component, but is preferably composed of an organic component capable of reducing the weight of the capacitor. More specifically, it may be composed of one or more kinds of resin components such as polyamide resin and polyolefin resin. In particular, it is preferably composed of a polyolefin resin so as not to be attacked by an ionic solution. For example, polyethylene resin (for example, ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer, etc.), polypropylene resin (for example, polypropylene, propylene copolymer) And a polymethylpentene resin (for example, polymethylpentene, methylpentene copolymer, etc.). Of these, ultrahigh molecular weight polyethylene and polypropylene are preferable.

The high-elasticity thick fiber of the present invention may be composed of the above resin component alone, or may be a mixture or a composite of two or more kinds of resin components. The cross-sectional shape of the highly elastic thick fiber composed of two or more kinds of resin components can be, for example, a core-sheath type, an eccentric type, or a sea-island type. If the resin component is composed of two or more kinds of resin components in this way, the resin component constituting the fiber surface can be fused.

It is preferable that such a high elastic thick fiber is contained in the fiber layer constituting the separator in an amount of 15 mass% or more so that the above-mentioned effect is easily exhibited.
It is more preferable that the content is 20 mass% or more, and 3
It is more preferable that the content is 0 mass% or more. On the other hand, from the relationship with the ultrafine fibers as described above, 95 mass
% Or less, more preferably 90 mass% or less, still more preferably 80 mass% or less.

The fiber diameter of this high elastic thick fiber is 10 μm.
When it is m or more, it is preferable that the mass ratio of the highly elastic thick fibers is 1 to 2.5 times the mass ratio of the ultrafine fibers as described above. This is because such a mass ratio tends to result in a state in which ultrafine fibers are present between the skeletons made of thick fibers having high elasticity.

Further, in addition to or in place of the high elasticity thick fiber as described above, it is preferable that the fused thick fiber is contained and the fused thick fiber is fused. By including such fused thick fibers, in addition to the effects of preventing breakage of the separator, ensuring ion permeability, and improving retention of the ionic solution, it is possible to improve the mechanical strength of the separator. Therefore, it is suitable for manufacturing a capacitor.

The fusion component of the fused thick fiber preferably has a melting point that does not adversely affect fibers other than the fused thick fiber (for example, ultrafine fibers, thick fibers having high elasticity). For example,
As the fibers other than the fused thick fiber, when the ultrafine fiber made of polypropylene resin alone and the high-elasticity thick fiber made of polypropylene resin alone are contained, as a fusion component of the fused thick fiber, polyethylene-based Resin (for example, ultra high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer, etc.) or propylene copolymer (for example, ethylene-butene-propylene copolymer) Polymer, ethylene-butadiene-propylene copolymer, ethylene-propylene copolymer, etc.) are preferable, and as fibers other than fusion-bonded thick fiber, ultrafine fibers made of polypropylene resin alone and ultrahigh molecular weight polyethylene. In the case of containing a single high elasticity fiber, the fusion component of the fusion thick fiber and Te, polyethylene (e.g., high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, etc.) for containing the or ethylene copolymer.

The fusion-bonded thick fiber may be composed of only the fusion-bonding component, or may contain a non-fusion-bonding component having a higher melting point than the fusion-bonding component in addition to the fusion-bonding component. When the latter is composed of a fusion component and a non-fusion component, the mechanical strength of the separator can be further improved. The cross-sectional shape of the fused thick fiber in this case may be, for example, a core-sheath type, an eccentric type, or a sea-island type. Further, the non-fusing component is preferably made of a resin which is higher than the melting point of the fusing component by 10 ° C. or more, more preferably 20 ° C. or more.

In order to improve the mechanical strength of the separator, the fused thick fiber is preferably contained in the fiber layer constituting the separator in an amount of 10 mass% or more, and 20 mass% or more. It is more preferable that the content is 30 mass% or more, and it is further preferable that the content is 30 mass% or more. On the other hand, it is preferably 95 mass% or less, more preferably 90 mass% or less, in view of the relationship with the ultrafine fibers or high elasticity thick fibers as described above, and 80
It is more preferable that the content is not more than mass%.

The fiber layer constituting the separator of the present invention is
It is not necessary to be composed only of the ultrafine fibers and the thick fibers as described above, and the fiber diameter exceeds 4 μm and the fiber diameter is 7 μm.
It may include less than the intermediate fibers, or may include a yarn in which the fibers are twisted together.

It is preferable that none of the fibers constituting the fiber layer of the separator of the present invention (for example, ultrafine fibers, high elastic thick fibers, fused thick fibers, intermediate fibers, etc.) be fibrillated. When it is composed of only fibers that are not fibrillated in this way, the texture is uniform, and since the ionic solution can be held in a good balance throughout the separator, it has excellent ion permeability and also has uniform ion permeability. Are better. The "non-fibrillated fiber" means a fiber in which fine fibers are not in an aggregated state, such as pulp.

The fibers constituting the fiber layer of the separator of the present invention (for example, ultrafine fibers, high elasticity thick fibers, fused thick fibers, intermediate fibers, etc.) are, as described above, organic and / or inorganic components. However, each fiber is preferably composed of an organic component so that the capacitor can be lightened. More specifically, polyamide-based resin, polyolefin-based resin, etc. 1
It can consist of more than one type. In particular, it is preferable that all the fibers are polyolefin fibers that are substantially composed of polyolefin resin so that they are not attacked by the ionic solution. This "polyolefin fiber consisting essentially of polyolefin resin" means that the part that is greatly affected by the ionic solution is the fiber surface, so the fiber surface (excluding both fiber ends) is A fiber that is composed. For example, a fiber that is composed of a polyamide resin and a polyolefin resin and has only the polyolefin resin occupying the fiber surface (excluding both ends of the fiber) is substantially a polyolefin fiber.

When all the resins constituting the fiber surface of the fibers (eg, ultrafine fibers, thick fibers, intermediate fibers, etc.) constituting the fiber layer of the separator of the present invention are made of the same type of resin, the fusion force between the fibers is increased. It is suitable because it is strong and does not easily break. In particular, it is preferable that all fiber surfaces are made of polypropylene resin. In addition, even when all the fusion components of the fibers constituting the fiber layer of the separator (for example, ultrafine fibers, thick fibers, intermediate fibers, etc.) are made of the same type of resin, the fusion force between the fibers is strong and it is difficult to break. Therefore, it is preferable. In particular, it is preferable that all the fusion components of the fibers are made of polyethylene resin.

The fibers constituting the fiber layer of the separator of the present invention (for example, ultrafine fibers, high elasticity thick fibers, fused thick fibers, intermediate fibers, etc.) can be in an unstretched state, but have excellent mechanical strength. As described above, the stretched state is preferable.

The fiber length of the fibers (eg, ultrafine fibers, high-elasticity thick fibers, fused thick fibers, intermediate fibers, etc.) constituting the fiber layer of the separator of the present invention is not particularly limited, The shorter the fiber length, the higher the degree of freedom of the fibers, and the more uniform the fibers can be dispersed.
It is preferably m. More preferably, it is a fiber cut to 1 to 20 mm. In addition, since the mechanical strength can be improved by including the filament fibers that are substantially continuous, it may be preferable to include the filament fibers in some cases.

Further, fibers constituting the fiber layer of the separator of the present invention (for example, ultrafine fibers, thick fibers, intermediate fibers, etc.)
In the case where the oxygen- and / or sulfur-containing functional group is introduced into the composition, it is well compatible with the ionic solution, and the fiber layer can highly retain the ionic solution, which is a preferred embodiment.

Examples of the oxygen- and / or sulfur-containing functional group include sulfonic acid group, sulfonate group, sulfofluoride group, carboxyl group, carbonyl group and hydroxyl group. Among these, it has been experimentally confirmed that the sulfofluoride group is particularly effective.

The fiber layer constituting the separator of the present invention is
It is preferable that they are fixed substantially only by fusion of the fibers. Since the fibers are fixed only by fusing as described above, the texture can be excellent, so that the ionic solution can be uniformly distributed and the ion permeability is excellent. For example, if the fibers are fixed by being entangled other than by fusion, the action for entanglement of the fibers (for example, a fluid flow such as water flow) disturbs the dispersion of the fibers, and As a result of the non-uniform distribution of the ionic solution, the ion permeability tends to deteriorate. However, if the ionic solution is fixed only by fusion, the dispersion of the fibers is not disturbed, and therefore the ion permeability is excellent.

The fibers may become entangled when forming the fiber layer. For example, even when the fiber web is formed by a card machine or the fiber web is formed by a wet method, the fiber web can maintain its shape to some extent. This indicates that the fibers are more or less entangled with each other. However, this degree of entanglement
Unlike the fluid entanglement described above, the entanglement does not disturb the dispersion of the fibers, and is therefore regarded as substantially not entangled in the present specification. As described above, “substantially only fusion of fibers” refers to a state in which the fibers are fixed to each other only by fusion after forming the fiber web. From another point of view, this state is a state in which the fibers (for example, ultrafine fibers, high elasticity thick fibers, fused thick fibers, intermediate fibers, etc.) that make up the fiber layer are substantially two-dimensionally arranged. .

The fiber layer of the separator of the present invention contains the ultrafine fibers, the thick fibers, and optionally the intermediate fibers as described above, but the state thereof is not particularly limited. That is,
These fibers may be mixed, or each fiber may independently exist in a layered form. Among these, when these fibers are mixed, the ultrafine fibers are uniformly dispersed, so that the ionic solution can be held uniformly and the ion permeability is excellent, which is preferable.

The separator of the present invention includes the fiber layer as described above, and the fiber layer may have a structure such as a non-woven fabric structure, a woven structure or a knit structure. Among these, a non-woven fabric structure that can form fine voids and is excellent in the retention of the ionic solution is preferable.

The separator of the present invention may be composed of only the fiber layer as described above, or may have another layer in addition to the fiber layer as described above. For example, a microporous membrane layer or the like may be provided. Among these, when the separator is composed of only the fiber layer, the ionic solution can be uniformly held in the entire separator and the ion permeability is excellent, which is a preferable mode.

As described above, the "formation index" can be mentioned as an index showing that the fibers are uniformly dispersed when the separator is composed of only the fiber layer. When the formation index is 0.15 or less, the fibers are uniformly dispersed, and the ionic solution can be held uniformly. A more preferable formation index is 0.10.

This "formation index" is disclosed in Japanese Patent Laid-Open No. 2001-509.
The value obtained by the method described in No. 02.
That is, it means the value obtained as follows. (1) Light is emitted from a light source to an object to be measured (separator), and among the emitted light, reflected light reflected in a predetermined region of the object to be measured is received by a light receiving element, and luminance information is acquired. To do. (2) Predetermined area of the object to be measured image size 3mm square, 6m
Equal division into m-square, 12 mm-square and 24 mm-square is performed to acquire four division patterns. (3) The brightness value of each section equally divided for each obtained division pattern is calculated based on the brightness information. (4) The luminance average (X) for each divided pattern is calculated based on the luminance value of each section. (5) Obtain the standard deviation (σ) for each divided pattern. (6) The coefficient of variation (CV) for each divided pattern is calculated by the following formula. Coefficient of variation (CV) = (σ / X) × 100 Here, σ represents the standard deviation of each divided pattern, and X represents the average brightness of each divided pattern. (7) A coordinate group obtained as a result of using the logarithm of each image size as the X coordinate and the coefficient of variation corresponding to the image size as the Y coordinate is regressed to a linear straight line by the least squares method, the slope is calculated, and this slope is calculated. The absolute value of is the formation index.

When the separator is composed of only the fiber layer, "maximum pore size" can be mentioned as another index showing that the fibers are uniformly dispersed.
When the maximum pore size is 40 μm or less, the fibers are uniformly dispersed, and the ionic solution can be uniformly held, so that the ion permeability is excellent. Since the smaller the maximum pore diameter is, the more uniform the dispersibility of the fibers is, and therefore, the diameter is more preferably 35 μm or less, further preferably 30 μm or less. The "maximum pore size" is a value measured by the bubble point method using a porometer (manufactured by Coulter Co.).

Further, when the separator is composed of only the fiber layer, as another index showing that the fibers are uniformly dispersed, "(maximum pore diameter / average flow pore diameter)"
The ratio can be mentioned. When this (maximum pore size / average flow rate pore size) ratio (= maximum pore size / average flow rate pore size) is 2 or less, (more preferably 1.9 or less), the pore size distribution of the fiber layer is narrow and the ionic solution becomes uniform. As a result of being distributable,
It is possible to manufacture a capacitor having excellent ion permeability. In addition, ideally, the maximum pore diameter and the average flow pore diameter are the same,
That is, the ratio of (maximum pore diameter / average flow pore diameter) is 1. This "average flow rate pore size" refers to a value obtained by the method specified in ASTM-F316, and is, for example, a porometer or Coulter.
r) manufactured by the company).

When the separator of the present invention comprises only the fiber layer, the porosity of the separator is preferably 45 to 65%, and preferably 50 to 60% so that the retention of the ionic solution and the ion permeability are excellent. It is more preferable.

The "porosity (P)" is a value obtained by the following equation. Porosity (P) = {1-W / (T × d)} × 100 Here, W means the surface density (g / m ² ), T means the thickness (μm) of the separator, and d Means the density (g / cm ³ ) of the resin forming the fibers of the separator (fiber layer). In addition, "area density" means the basis weight obtained based on the method prescribed | regulated to JIS P8124 (paper and board-basis weight measuring method). When two or more kinds of resins constituting the fibers of the fiber layer are present, the resin density means the mass average of the resins. For example, the resin A having the density d ₁
Is a (mass%) and the resin B having a density d ₂ is b (mass).
s%) When present, the resin density refers to the value obtained by the following equation. d = d ₁ × a / 100 + d ₂ × b / 100

Further, when the separator of the present invention is composed of only the fiber layer, if the tensile strength of the separator in at least one direction is 20 N / 5 cm width or more, the electrode plate group can be formed without breaking the separator. Therefore, the capacitor can be manufactured with high yield. More preferable tensile strength is 30 N / 5 cm width or more, 40 N
More preferably, the width is / 5 cm or more. When the capacitor is manufactured, tension acts mainly in the longitudinal direction of the separator, so the tensile strength is preferably in the longitudinal direction of the separator. This "tensile strength" is 5 cm in a direction orthogonal to a certain direction, and a rectangular separator cut into a length of 20 cm in a certain direction is used as a tensile strength tester (manufactured by Orientec, Tensilon UTM-III). -100) between chucks (distance between chucks: 10 cm), and pulling speed 300 mm / mi
n is the force required to pull the separator and break the separator.

The thickness of the separator of the present invention is not particularly limited, but the thinner the separator,
Since it is excellent in ion permeability, it is preferably 600 μm or less, more preferably 400 μm or less, and further preferably 200 μm or less. On the other hand, if the thickness of the separator is too thin, the electrical insulation performance, which is the original function of the separator, may be impaired.
It is preferably not less than 30 μm, more preferably not less than 30 μm, further preferably not less than 40 μm.

This "thickness" is defined by JIS B 7502:
The outside micrometer (0 to 0 specified in 1994
25 mm) and JIS C 2111 5.1
The average value of 10 randomly selected points measured by the measuring method of (1).

The areal density of the separator of the present invention is not particularly limited, but as the areal density increases, the thickness tends to increase, and as the areal density decreases, the thickness decreases. Since it tends to be thin, the thickness as described above is easily adjusted to 10 to 300 g / m ²
It is preferably at, more preferably from 20 to 200 g / m ^2, and even more preferably 30 to 100 g / m ^2.

The needle type penetration resistance of the separator of the present invention is preferably 500 gf or more. In other words, it is common to use activated carbon fine particles with a large specific surface area as the electrodes that compose the capacitor so that the amount of charge can be increased, but in order to bring such electrodes into close contact with the separator, a high pressure is applied. Then, since the activated carbon is fine particles, it may penetrate the separator and impair the electrical insulation property. Therefore, the needle penetration resistance as described above is preferably 500 gf or more. A more preferable needle type penetration resistance is 600 gf or more, and a further preferable needle type penetration resistance is 700 gf or more.

The needle penetration resistance is a value obtained as follows. One separator is placed so as to cover the cylindrical through hole of the support base having the cylindrical through hole (inner diameter: 11 mm), and a fixing material having the cylindrical through hole (inner diameter: 11 mm) is further placed on the separator. The fixing member is placed so that the center of the fixing member coincides with the center of the cylindrical through hole of the support, and the separator is fixed. Then, for this separator, handy compression tester (KATO TECH, KE
S-G5) needle (curvature radius at tip: 0.5 mm, diameter: 1 mm, protrusion length from jig: 2 cm) was vertically pierced at a speed of 0.01 cm / s, and the needle was Measure the force required to penetrate,
This force is defined as the needle type penetration resistance.

As described above, the separator of the present invention does not break even when a high pressure is applied to bring it into close contact with the electrode, has excellent ion permeability, and has excellent ionic solution retention. Therefore, it can be applied to various electric double layer capacitors. For example, an electric double layer capacitor whose ionic solution is an aqueous solution,
The ionic solvent can be used for an organic electric double layer capacitor, and in particular, the ionic solution can be preferably used as a separator for an electric double layer capacitor in which a sulfuric acid aqueous solution is used.

The separator of the present invention can be manufactured, for example, as follows. First, in order to form the fiber layer of the separator, the ultrafine fibers and / or the splittable fibers and the thick fibers (preferably the highly elastic thick fibers and / or the fusion-bonded thick fibers) as described above, and optionally the intermediate fibers are prepared. . Then, using these fibers, a non-woven structure is formed by a conventional method,
A fiber layer having a woven structure or a knit structure is formed.

In the case of a fiber layer having a preferred non-woven structure, the prepared fiber is used to form a fiber web. The method for forming this fiber web is not particularly limited,
For example, dry method (eg, card method, air-ray method, etc.)
Or a wet method. Among these, it is preferable to form by a wet method so that the fibers are more uniformly dispersed and a non-woven fabric structure capable of holding an ionic solution uniformly in the entire fiber layer is easily formed. This wet method can be formed by a conventionally known method, for example, a horizontal Fourdrinier method, an inclined wire type short reticulated method, a cylinder method, or a Fourdrinier / cylinder combination method.

Then, the fibers constituting the fiber web can be fixed to form a fiber layer having a non-woven fabric structure. The fixing of the fibers can be carried out by entanglement and / or fusion. As the former method of entanglement, there is a method of applying a fluid flow such as a water flow or a needle, and according to this method, even if the fibrous web contains the splittable fiber, the splittable fiber is By dividing, ultrafine fibers can be generated. As the latter method of fusing, fiber web constituent fibers (for example, ultrafine fibers, splittable fibers, high elastic thick fibers, fused thick fibers, intermediate fibers, etc.)
There is a method of heat-bonding the fusion component of, and if it is this method, the dispersion of the fibers is not disturbed, the texture is excellent, and the ionic solution can be uniformly distributed, so that the ion permeability An excellent fiber layer can be formed.

The condition for the entanglement by the fluid flow is not particularly limited as long as it does not significantly disturb the texture of the fiber web, but for example, the nozzle diameter is 0.05.
~ 0.3 mm, pitch 0.2 ~ 3 mm, nozzles arranged in one row or in two or more rows, pressure 1MP
A fluid flow of a to 30 MPa may be ejected. Such a fluid stream is jetted once or more to one or both sides of the fibrous web. When the non-perforated part of the support (eg, net, perforated plate) on which the fiber web is placed is thick when treated with the fluid flow, the obtained fiber layer also has large pores, which results in ionicity. Since not only the uniform distribution of the solution is impaired but also the electric insulating property tends to be deteriorated, it is preferable to use a support having a non-opened portion with a thickness of 0.25 mm or less.

On the other hand, when fusing a fibrous web,
It may be carried out under no pressure, may be carried out under pressure, or may be pressurized (preferably immediately under pressure) after the fusion component is melted under no pressure. In any case, the heating temperature is preferably in the range from the softening temperature of the fusion component to a temperature 30 ° C. higher than the melting point,
When pressure is applied, the porosity of the fiber layer is 45 to 65%.
Therefore, it is preferable to appropriately adjust the tensile strength in at least one direction (preferably the longitudinal direction) to be 20 N / 5 cm width. The "softening temperature" means a temperature which gives a starting point of a melting endothermic curve obtained by using a differential calorimeter to raise the temperature from room temperature at a temperature rising rate of 10 ° C / min.

Further, since the ion permeability can be increased by making the fiber layer thin, when the fiber layer is thicker than necessary, the thickness can be increased by passing it between a pair of rolls. It is preferably adjusted.

A fiber layer having a formation index of 0.15 or less, a fiber layer having a maximum pore diameter of 40 μm or less, which is an index showing that the fibers are uniformly dispersed in the fiber layer of the present invention, or (maximum pore diameter / The fiber layer having a ratio of average flow pore diameters of 2 or less has a large amount of ultrafine fibers, uses fibers which are not fibrillated as fibers constituting the fiber layer, and has a short fiber length of about 1 to 20 mm. It can be manufactured by using fibers in combination, forming a fiber web by a wet method, fixing the fibers only by fusion (no entanglement treatment), or by using these in combination.

The fiber layer having a porosity of 45 to 65% according to the present invention is used in combination with such as by reducing the amount of ultrafine fibers, reducing the amount of fibers used, and adjusting the pressure during fusion. Can be manufactured.

The fiber layer having a tensile strength of at least 20 N / 5 cm width in at least one direction (preferably the longitudinal direction) of the present invention is adjusted by adjusting the moving speed of the net for making the fibers and the slurry flow rate. It can be produced by using them in combination such that the orientation is close to one direction, the degree of fusion is increased, or the fiber length is increased.

The needle type penetration resistance of the present invention is 500 gf.
The above separators use high elastic thick fibers with a large Young's modulus, increase the amount of high elastic thick fibers, uniformly disperse the high elastic thick fibers, or firmly fuse them by fusing thick fibers. It can be manufactured by adjusting various conditions such as fusing and fusing immediately after melting the fused thick fiber.

Since the fibers constituting the fiber layer of the present invention are preferably substantially composed of polyolefin fibers so as not to be attacked by the ionic solution, the retention of the ionic solution is improved. Therefore, it is preferable to introduce an oxygen- and / or sulfur-containing functional group into the surface of the fiber forming the fiber layer. As a method of introducing such a functional group, for example, sulfonation treatment, fluorine gas treatment,
A discharge treatment etc. can be mentioned. The fiber layer may be formed after introducing the oxygen- and / or sulfur-containing functional group into each fiber, or the oxygen- and / or sulfur-containing functional group may be introduced after forming the fiber layer. Hereinafter, the case of introducing an oxygen- and / or sulfur-containing functional group into the fiber layer will be described, but the same applies to the case of introducing an oxygen- and / or sulfur-containing functional group into the fiber. A containing functional group can be introduced.

The sulfonation treatment is not particularly limited. For example, the fiber layer as described above is dipped in a solution containing fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuric acid, or sulfuryl chloride. Introducing a sulfonate group and / or a sulfonate group into the fibers constituting the fiber layer, or by causing an electric discharge in the presence of sulfur monoxide gas, sulfur dioxide gas, or sulfur trioxide gas, Sulfonic acid groups and / or sulfonic acid groups can be introduced into the constituent fibers.

The fluorine gas treatment is also not particularly limited, but, for example, fluorine gas diluted with an inert gas (eg, nitrogen gas, argon gas, etc.), oxygen gas, carbon dioxide gas, and sulfur dioxide gas are used. The sulfofluoride group or the like can be introduced into the fibers constituting the fiber layer by exposing the fiber layer to a mixed gas of at least one kind of gas selected from the above.

Examples of the discharge treatment include corona discharge treatment, plasma treatment, glow discharge treatment, creeping discharge treatment, and electron beam treatment. Among these discharge treatments, under atmospheric pressure in the air, each carries a dielectric, and between the pair of electrodes arranged so that the dielectrics face each other, the fibers are contacted with both of these dielectrics. A method of arranging layers and applying an AC voltage between these two electrodes to generate a discharge in the internal voids of the fiber layer is that not only on the outside of the fiber layer but also on the surface of the fibers forming the inside of the fiber layer. Also, a carboxyl group, a carbonyl group, a hydroxyl group or the like can be introduced. Therefore, the retention of the ionic solution and the ion permeability inside the fiber layer are excellent, and the life of the capacitor can be extended.

The fiber layer produced as described above can be used as it is as a separator. When it contains a microporous membrane layer in addition to such a fiber layer, it is then heat-laminated. The separator of the present invention can be manufactured by integrating the fiber layer and the microporous membrane layer.

Examples of the separator of the present invention will be described below, but the present invention is not limited to these examples.

[0089]

[Example] (Example 1) As a sea-island type composite fiber, poly-
A fiber obtained by a composite spinning method in which 25 island components made of polypropylene are present in a sea component made of L-lactic acid (hereinafter referred to as “PLLA”) (fineness: 1.65 dt
ex, cut fiber length: 2 mm, melting point: 172 ° C.) was prepared.

Next, this sea-island type composite fiber was heated at a temperature of 80.
C., which is a sea component of sea-island type composite fiber
By extracting and removing LLA, polypropylene ultrafine fibers (fiber diameter: 2 μm, average fiber diameter: 2 μm, ρ / d: 0.08)
3, melting point: 172 ° C., cut fiber length: 2 mm, average fiber length: 2 mm, density: 0.91 g / cm ³ , unfibrillated, stretched, diameter does not substantially change in the fiber axis direction, Fiber cross-sectional shape: circular) was obtained.

As the fused thick fiber, the core component (non-fused component) is polypropylene (melting point: 168 ° C., density: 0.
91 g / cm ³ ) and the sheath component (fusion component) is high-density polyethylene (melting point: 135 ° C., density: 0.96 g /
cm ³ ) core-sheath composite thick fiber (fineness: 0.8 dt
ex, fiber diameter: 10.5 μm, average fiber diameter: 10.5 μ
m, cut fiber length: 5 mm, mass ratio of core component to sheath component is 1: 1, unfibrillated, stretched)
Prepared.

Further, as the highly elastic thick fiber, a thick fiber made of highly crystalline polypropylene (Young's modulus: 90 cN / dt) is used.
ex, fineness: 1.3 dtex, fiber diameter: 13.5 μm,
Average fiber diameter: 13.5 μm, cut fiber length: 10 mm, average fiber length: 10 mm, density: 0.91 g / cm ³ , unfibrillated, stretched) were prepared.

Next, the polypropylene ultrafine fibers 20
mass%, core-sheath type composite thick fiber 50 mass%, and polypropylene high elastic thick fiber 30 mass% are mixed,
Fibers were mixed uniformly from the dispersed slurry by a wet method (horizontal Fourdrinier method) to form a dispersed fiber web.

Then, this fiber web was left for 3 minutes in a hot air circulation dryer set at a temperature of 135 ° C.,
The fibers were fixed to each other by drying the fiber web and substantially heat-sealing the core-sheath type composite thick fibers with a sheath component (high-density polyethylene) to form a fused non-woven fabric.

Next, the fused nonwoven fabric was calendered to produce a separator substrate.

Next, this separator substrate was treated with 3 vol% of fluorine gas, 5 vol% of oxygen gas and 5 vol% of sulfur dioxide gas.
The sulfofluoride group is introduced to the fiber surface by contacting with a mixed gas consisting of vol% and 87 vol% of nitrogen gas for 120 seconds, and the separator of the present invention (area density: 40 g / m ² , thickness: 100 μm). ) Was manufactured.
The average fiber diameter of the thick fibers forming this separator was 5.5 times the average fiber diameter of the ultrafine fibers.

(Comparative Example 1) A nozzle piece having orifices having a diameter of 0.2 mm arranged at a pitch of 0.7 mm was prepared, polypropylene resin was supplied to the nozzle piece, and the nozzle piece was heated to a temperature of about 260 ° C. It was heated and discharged in an amount of 0.09 g per orifice per minute. Next, the discharged polypropylene fibers were blown with air heated to a temperature of 270 ° C. to be ultrafine, and then the ultrafine polypropylene fibers were opened by 0.99.
Fiber web (average fiber diameter: 3 μm) made of ultrafine polypropylene fibers (not fibrillated, unstretched, diameter changes in the fiber axis direction, fiber cross-sectional shape: circular) collected by a 1 mm net Was formed.

Next, this fibrous web was placed on a plain weave net having an opening of 0.175 mm, and then a water flow having a pressure of 12 MPa was applied from a nozzle plate having a nozzle pitch of 0.6 mm and a nozzle diameter of 0.13 mm. The fibers were entangled with each other by alternately jetting twice on both sides of the fiber web to form an entangled meltblown nonwoven fabric.

Then, the entangled melt-blown nonwoven fabric was calendered to produce a separator substrate.

Next, this separator substrate was treated with 3 vol% of fluorine gas, 5 vol% of oxygen gas and 5 v of sulfur dioxide gas.
sol% and 87 vol% of nitrogen gas were brought into contact with the mixed gas for 120 seconds to introduce sulfofluoride groups on the fiber surface, and a separator for comparison (area density: 40 g / m ² , thickness: 70 μm) Was manufactured.

(Comparative Example 2) The same fused thick fiber and high elastic thick fiber as in Example 1 were mixed in a mass ratio of 50:50 and dispersed to obtain a fiber by a wet method (horizontal Fourdrinier method). A sulfofluoride group was introduced on the fiber surface by the same procedure as in Example 1 except that a web was formed.
Comparative separator (area density: 40 g / m ² , thickness: 20
0 μm) was produced.

(Measurement of Formation Index) The formation index of each separator was measured as follows. (1) Light is radiated from a light source to a DUT (separator), and among the radiated light, reflected light reflected in a predetermined region of the DUT is received by a light receiving element to obtain luminance information. . (2) Predetermined area of the object to be measured image size 3mm square, 6m
Four division patterns were acquired by equally dividing into m square, 12 mm square, and 24 mm square. (3) The brightness value of each section equally divided for each obtained division pattern was calculated based on the luminance information. (4) The luminance average (X) for each divided pattern was calculated based on the luminance value of each section. (5) The standard deviation (σ) of each divided pattern was obtained. (6) The coefficient of variation (CV) for each divided pattern was calculated by the following formula. Coefficient of variation (CV) = (σ / X) × 100 Here, σ represents the standard deviation of each divided pattern, and X represents the average brightness of each divided pattern. (7) The coordinate group obtained as a result of the logarithm of each image size being the X coordinate and the coefficient of variation corresponding to the image size being the Y coordinate is regressed to a linear line by the least squares method, the slope is calculated, and this slope is calculated. The absolute value of was used as the formation index. The smaller the formation index, the more uniformly the fibers are dispersed. The results are shown in Table 1.

[0103]

[Table 1]

(Measurement of Maximum Pore Diameter) The maximum pore diameter of each separator was measured by the bubble point method using a porometer (manufactured by Coulter Co.). This value was as shown in Table 1.

(Measurement of (maximum pore diameter / average flow pore diameter) ratio)
The average flow pore size of each separator is
It was measured by the mean flow point method using a meter, manufactured by Coulter.

Then, based on the maximum pore diameter value obtained as described above, the ratio (maximum pore diameter / average flow pore diameter) was calculated. The results are shown in Table 1.

(Measurement of Porosity) First, the surface density (W) and the thickness (T) of each separator were measured.

Next, the resin density (d) of the constituent fibers of the separator was calculated from the density and mass ratio of each constituent fiber.

Then, the "porosity (P)" was calculated from the following formula. Porosity (P) = {1-W / (T × d)} × 100 The results are shown in Table 1.

(Measurement of Tensile Strength in Longitudinal Direction) Tensile strength test was performed on each rectangular separator cut into a length of 5 cm in a direction (width direction) orthogonal to the longitudinal direction and a length of 20 cm in the longitudinal direction. Machine (Tensilon UTM-III-100 manufactured by Orientec) was fixed between the chucks (distance between chucks: 10 cm), and the pulling speed was 300 mm / mi.
Each separator was pulled in the longitudinal direction by n, and the force required to break each separator was measured, and this force was taken as the tensile strength in the longitudinal direction. The results are shown in Table 1.

(Needle-type Penetration Resistance) One separator is placed so as to cover the cylindrical through hole of the support base having the cylindrical through hole (inner diameter: 11 mm), and the cylindrical through hole is placed on each separator. A fixing material having a hole (inner diameter: 11 mm) is placed so that the center of the fixing material coincides with the center of the cylindrical through hole of the support table, and each separator is fixed. Needle (radius of curvature at tip: 0.5 mm, diameter: 1 m) attached to a compression tester (KES-G5, manufactured by Kato Tech)
m, the protruding length from the jig: 2 cm) is 0.01 cm /
The needle was pierced vertically at a speed of s and the force required for the needle to penetrate was measured, and this force was taken as the needle type penetration resistance. The results are shown in Table 1.

(Measurement of Electric Conductivity) Each separator was sandwiched between circular electrodes made of platinum having a diameter of 20 mm, which were placed in a test cell for measuring electric conductivity, and 30% by weight was obtained.
After filling the test cell with a dilute sulfuric acid electrolytic solution (20 ° C.), a pressure of 0.56 MPa was applied between the electrodes, and the electrical conductivity in the thickness direction of each separator was measured based on the AC impedance method. , And was evaluated as a value indicating ion permeability. A separator having an electric conductivity of 5 × 10 ⁻⁴ S / cm or more is practically suitable. The results are shown in Table 1.

(Measurement of pressurized liquid retention rate) Each separator cut into a diameter of 30 mm was allowed to reach water equilibrium in an environment of a temperature of 20 ° C. and a relative humidity of 65%, and then the mass (M ₀ ) Was measured.

Next, the dilute sulfuric acid solution was held by immersing it in a dilute sulfuric acid solution of 30% by weight (20 ° C.) for 1 hour so that the air in each separator was replaced with the dilute sulfuric acid solution.

Next, each separator was sandwiched between three upper and lower filter papers (diameter: 30 mm), and a pressure pump was used to hold the separator at 5.7.
After applying a pressure of MPa for 30 seconds, the mass (M ₁ ) of each separator was measured.

Then, the liquid retention under pressure was determined by the following formula. This measurement was carried out at four points on each separator, and the average was taken as the pressurized liquid retention rate. The results are shown in Table 1. Liquid retention under pressure (%) = {(M ₁ −M ₀ ) / M ₀ } × 100

As is clear from Table 1, the separator of the present invention has a high electric conductivity and an excellent ion permeability, and has a high pressure-holding rate and an excellent electrolyte holding ability. It could be lengthened.
It was predicted that this is because the separator of the present invention was provided with the fiber layer containing the ultrafine fibers and the thick fibers, the fibers were uniformly dispersed, and the ionic solution could be uniformly retained.

On the other hand, the separator of Comparative Example 1 is composed of only ultrafine fibers, has a small porosity, and is easily deformed by pressure to easily become a more dense structure. Was low in ion permeability. Further, the separator of Comparative Example 2 is composed of only thick fibers and has a large porosity, but probably because the fiber surface area that can be involved in holding the ionic solution is small.
The liquid retention under pressure was low and the retention of the ionic solution was poor.

[0119]

The separator for an electric double layer capacitor of the present invention can prevent the separator from breaking due to the presence of the thick fibers even when a high pressure is applied, and even when a high pressure is applied, the thick fibers can be prevented. It is possible to secure a certain amount of voids by virtue of the presence of the microcapsules, and it is also possible to manufacture a capacitor with excellent ion permeability and a long life because it has excellent retention of an ionic solution by containing ultrafine fibers. It is a possible separator.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) D21H 13/00 D01F 8/14 Z 13/14 H01G 9/00 301C 15/10 D06M 9/04 // D01F 8/06 7/02 A 8/14 F term (reference) 4L031 AA14 AA18 AB10 AB11 AB34 AB36 BA11 BA17 CA01 CA02 DA21 4L041 AA07 BA02 BA04 BA05 BA16 BA24 BC20 BD12 BD20 CA05 CA36 CA38 DD01 DD05 DD11 4L047 AA14 AA21 AA27 AA28 AB08 AB08 AB08 BA09 BB01 BB09 CB01 CB08 CC12 4L055 AF16 AF17 AF44 AF46 AF47 BE11 BE20 EA01 EA16 FA13 FA15 FA30 GA01 GA31 GA50

Claims (9)

[Claims] 1. A separator for an electric double layer capacitor, comprising a fiber layer containing ultrafine fibers having a fiber diameter of 4 μm or less and thick fibers having a fiber diameter of 7 μm or more. 2. The separator for an electric double layer capacitor according to claim 1, wherein the ultrafine fibers include ultrafine fibers formed by removing the sea component of the sea-island type composite fiber. 3. The thick fiber has a Young's modulus of 50 cN / d.
The separator for an electric double layer capacitor according to claim 1 or 2, characterized in that it contains high-elasticity thick fibers of tex or more. 4. The thick fibers include fused thick fibers, and the fused thick fibers are fused.
The separator for an electric double layer capacitor according to any one of claims 1 to 3. 5. The separator for an electric double layer capacitor according to claim 1, wherein none of the fibers constituting the fiber layer are fibrillated. 6. The separator for an electric double layer capacitor according to claim 1, wherein the average fiber diameter of the thick fibers is 5 times or more the average fiber diameter of the ultrafine fibers. 7. The separator for an electric double layer capacitor according to claim 1, wherein the fiber layer is substantially composed of a polyolefin-based fiber. 8. An oxygen- and / or sulfur-containing functional group is introduced into the fiber constituting the fiber layer,
A separator for an electric double layer capacitor according to any one of claims 1 to 7. 9. The method according to claim 1, wherein the ionic solution is used for an electric double layer capacitor based on an aqueous solution.
A separator for an electric double layer capacitor according to claim 8.