JP2003303738A - Separator for capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator of an electric double layered capacitor using electrolyte, which is easy to set its electric resistance by adjusting the porosity, superior in retaining the electrolyte, suppresses the dry-out phenomenon of the capacitor, and further, does not form pin holes by fallen materials, and contributes to increase the life of the capacitor. <P>SOLUTION: The fine porous capacitor separator using electrolyte of an aqueous or non-aqueous system is characterized in that the separator material is composed of polyolefin system resin and inorganic powder, and the electric resistance is adjusted by leaving an oil-like material insoluble to the electrolyte in some of the holes. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous separator for capacitors using an aqueous or non-aqueous electrolyte, and more particularly to a microporous separator for electric double layer capacitors.

[0002]

2. Description of the Related Art A microporous film mainly composed of a polyolefin resin has been used as a separator for capacitors and storage batteries using an electrolytic solution, and has been widely used in recent years for the rapid spread of portable electronic devices. As a result, the scope of application and demand are expanding. Some electric double layer capacitors using an electrolytic solution use an aqueous solution type or non-aqueous type electrolytic solution. Therefore, it is necessary to consider the chemical resistance to the above-mentioned two types of electrolytes as the material of the separator to be used, and in the case of an electric double layer capacitor using an aqueous electrolyte such as dilute sulfuric acid, a polyolefin resin is used. In particular, polyethylene and polypropylene are commonly used. A capacitor separator mainly composed of such a resin is required to have various characteristics such as a function of preventing short circuit between electrodes, ion conductivity, and impregnation property of an electrolytic solution as basic functions. Is important. In order to prevent short circuit and increase of self-discharge caused by the electrode material penetrating into the pores of the separator, the fine pores of the separator should be smaller than the particle diameter of the electrode material. The heat treatment during capacitor assembly and the thermal stability of the separator when used at high temperatures do not cause blockage of fine holes or dimensional change. High electrolyte retention in the separator micropores to prevent electrolyte dryout that occurs when capacitors are used. It must have the mechanical strength required when assembling capacitors. In addition to the above requirements, in an electric double layer capacitor that uses an aqueous electrolyte, a method of reducing self-discharge is to use a separator with a relatively low porosity and a high electric resistance. A method of increasing the internal resistance of a multilayer capacitor and suppressing self-discharge is known,
Ease of adjusting the porosity is also important in manufacturing the separator.

As a separator for a capacitor using an electrolytic solution, as described in JP-A-3-278512, a mixture containing an olefin resin such as polypropylene and an inorganic powder such as diatomaceous earth is molded and stretched. By applying the separator obtained by the above to the electric double layer capacitor, it has been shown that self-discharge and leakage current are extremely reduced, but since the pores are formed by stretching the film, Although it has the advantage that the porosity of the separator can be adjusted within a certain narrow range by adjusting the degree of stretching, since the inorganic powder is not filled in the pores, the electrolyte holding power is low and the electrolyte dryness is low. The effect of suppressing the out phenomenon is small.

Further, in order to reduce the leakage current and prevent a short circuit, a separator for an electrolytic capacitor obtained by impregnating and applying a dispersion liquid in which a silica-based powder is dispersed into a synthetic fiber web made of polyolefin resin or the like is disclosed. 57-
As disclosed in JP-A-2006018, since the silica-based powder is impregnated and applied to be carried on the synthetic fiber web, pin holes are generated due to the silica-based powder falling off at the time of assembling the capacitor, and at the time of assembling the capacitor. There was a problem that the work environment became dirty.

[0005]

As described above, in the conventional porous separator for a capacitor, the method disclosed in Japanese Laid-Open Patent Publication No.
The effect of suppressing the dryout phenomenon of the electrolytic solution is small as in the separator described in Japanese Patent No. 278512,
As in the separator described in Japanese Patent Laid-Open No. 57-206018, there is a problem that a part of the separator material falls off, which causes pinholes and the working environment becomes dirty during capacitor assembly. Further, there has not been disclosed a method for producing a separator that can adjust the electric resistance of the separator relatively easily.

In order to solve such conventional problems, the present invention makes it possible to easily set the electric resistance of the separator based on the porosity adjustment in an electric double layer capacitor separator using an electrolytic solution, and to An object of the present invention is to provide a separator for an electric double layer capacitor, which has a high liquid retention ability, can suppress the dryout phenomenon of the capacitor, and can contribute to the longevity of the capacitor without causing pinholes due to material dropout or the like. .

[0007]

In order to achieve the above-mentioned object, the capacitor separator of the present invention has a microporous structure for a capacitor using an aqueous or non-aqueous electrolytic solution as set forth in claim 1. In the separator, the constituent material of the separator is made of a polyolefin resin and an inorganic powder, and an oily substance insoluble in the electrolytic solution is left in a part of the separator pores to be adjusted to a predetermined electric resistance value. It is characterized by The capacitor separator according to claim 2 is the capacitor separator according to claim 1, wherein the oily substance insoluble in the electrolytic solution is one or two selected from paraffin-based or naphthene-based hydrocarbon compounds. It is characterized by being a mixture of two or more species.
The capacitor separator according to claim 3 is the capacitor separator according to claim 1 or 2, wherein
It is characterized in that the average pore diameter by the mercury intrusion method is 0.1 μm or less. The capacitor separator according to claim 4 is the capacitor separator according to any one of claims 1 to 3, wherein the polyolefin-based resin contains ultra high molecular weight polyethylene having a weight average molecular weight of 500,000 or more, The inorganic powder is mainly composed of silica. The capacitor separator according to claim 5 is the capacitor separator according to any one of claims 1 to 4, wherein the composition ratio (mass ratio) of the polyolefin resin and the inorganic powder is 2: 8 to.
It is characterized by being set to 8: 2, and more preferably 2: 8 to 5: 5. The method for producing a capacitor separator according to the present invention is, as described in claim 6, a microporous separator for a capacitor using an aqueous or non-aqueous electrolyte, wherein the constituent material of the separator is a polyolefin. A method for producing a separator for a capacitor, comprising a resin and an inorganic powder, wherein an oily substance insoluble in an electrolytic solution is left in a part of the pores of the separator to adjust to a predetermined electric resistance value. A film is manufactured by an extrusion method from a raw material composition in which a resin, an inorganic powder, and an oily substance insoluble in an electrolytic solution are mixed, and then the oily substance is extracted and removed from the film using an extractant, and a predetermined amount of It is characterized in that the porosity is adjusted so that the oily substance remains in the separator.

As described above, according to the present invention, in the production thereof, the raw material composition obtained by mixing the polyolefin resin, the inorganic powder and the oily substance insoluble in the electrolytic solution is extruded into a film, and then the film is extruded. Since the oily substance was extracted and removed from the film using a suitable extractant to obtain a porous film, a porous film having a fine and uniform pore size in which the inorganic powder was filled in the pores was obtained. be able to. Further, when extracting and removing the oily substance using the extractant, by leaving a predetermined amount of the oily substance in the separator, the porosity of the separator can be easily adjusted to any desired value. It is a thing.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in order to manufacture the separator for an electric double layer capacitor of the present invention, a polyolefin resin, an inorganic powder, and an oily substance having a plasticizer function are used as raw material compositions. Prepare a mixture of. Then, the raw material composition is extruded from a die while being heated and melted and kneaded by using an extruder, and is pressure-molded by a molding roll to form a film, and the oil-like material is entirely prepared by using an appropriate extractant. Alternatively, it can be obtained by uniformly extracting and removing a part thereof. In the case of a capacitor separator that uses an aqueous electrolyte solution, a surfactant may be added to the raw material composition or a surfactant solution may be used for the purpose of improving wettability with respect to the electrolyte solution. It is necessary to post-treat the porous film, and anionic or nonionic surfactants can be used, but especially when sulfuric acid is used as the electrolytic solution, sodium dialkylsulfosuccinate commonly used in lead acid battery separators. The use of salt is preferred.

As the polyolefin resin, polyethylene, polypropylene, polybutene and their copolymers or mixtures can be used. In particular, the mechanical strength can be secured by using a polyethylene resin having a weight average molecular weight of 500,000 or more, but more preferably,
By using high-density polyethylene having a weight average molecular weight of 2,000,000 or more, a separator having excellent mechanical strength can be obtained. It is also possible to mix and use resins having different weight average molecular weights, for example, to mix and use both a high density polyethylene resin having a weight average molecular weight of 2,000,000 and a low density polyethylene having a weight average molecular weight of less than 500,000. It is possible.

The inorganic powder has a specific surface area of 100.
It is possible to use one or a mixture of two or more kinds selected from stable inorganic powders in an electrolytic solution such as silica, titania, and alumina having a m ² / g or more, but silica is relatively inexpensive and has a small amount of impurities. preferable. The specific surface area is 100
An inorganic powder of less than m ² / g is not preferable because it has a small effect of imparting electrolyte holding power and a small effect of suppressing dryout of the capacitor.

As the oily substance insoluble in the electrolytic solution,
It is necessary to select a substance that acts as a plasticizer for the polyolefin resin, for example, one or a mixture of two or more selected from paraffin hydrocarbons and naphthene hydrocarbons (eg process oil), phthalic acid. Dioctyl,
Phthalates such as dibutyl phthalate, sebacates, adipates, phosphates, oleates, stearates and the like can be used. In particular, the process oil is applicable to both the aqueous solution type and the non-aqueous type electrolytic solution, and is preferable in that it has little influence on the environment. On the other hand, the above-mentioned esters are applicable to aqueous electrolytes, and for non-aqueous electrolytes,
It cannot be applied because it dissolves in the electrolyte and also has a large environmental impact.

The organic solvent used as the extractant for the oily substance must be a poor solvent for the olefinic resin and a good solvent for the oily substance. For example, n -Hexane or cyclohexane, n
Hydrocarbons such as decane, halogenated hydrocarbons such as 1,1,1-trichloroethane, alcohols such as isopropanol, ethers such as diethyl ether, and ketones such as acetone can be used.

The composition ratio (mass ratio) of the polyolefin resin and the inorganic powder in the separator of the present invention is 2: 8 to.
Although it is applicable in the range of 8: 2, from the viewpoint of adjusting the porosity of the separator by allowing the oily matter to remain in the separator pores, in the sense of widening the adjustment range of the porosity,
It is preferably in the range of 2: 8 to 5: 5. In the composition ratio between the above two, if the composition ratio of the polyolefin-based resin is less than 2/10 (less than 20%), the mechanical strength of the separator is insufficient, which is not preferable, and the composition ratio of the polyolefin-based resin is 8 /. If it exceeds 10 (exceeds 80%), the composition ratio of the inorganic powder becomes less than 2/10 (less than 20%), and the electrolytic solution holding power becomes small, which is not preferable.

[0015]

EXAMPLES Next, examples of the present invention will be described. In the following Examples and Comparative Examples, "part" which is a unit for indicating the blending amount indicates "part by mass" unless otherwise specified. (Example 1) 30 parts of a high-density polyethylene resin having a weight average molecular weight of 2,000,000 and 70 parts of a silica powder having a specific surface area of 250 m ² / g were mixed with 100 parts of mineral oil, and heated and melted and kneaded by an extruder. While extruding from a T-die and pressure-molded with a molding roll, a film having a thickness of 100 μm was obtained.
The mineral oil in this film was extracted and removed with n-hexane so as to leave a certain amount thereof, and then dried to obtain 29.7% by mass of polyethylene resin, 69.3% by mass of silica powder, and 1% by mass of mineral oil. % Microporous film was obtained with a thickness of 100 μm. Next, this film was treated with an ethanol solution containing 0.5% by mass of dialkylsulfosuccinic acid sodium salt to impart permeability to an electrolytic solution to obtain a capacitor separator.

Example 2 Polyethylene was prepared in the same manner as in Example 1 except that the mineral oil was extracted and removed so that a larger amount of the mineral oil was left in the film. Resin 27 mass%, silica powder 63
100 μm thickness consisting of 10% by weight of mineral oil and 10% by weight of mineral oil
The microporous porous film of No. 1 was obtained, and permeability to the electrolytic solution was imparted in the same manner as in Example 1 to obtain a capacitor separator.

(Embodiment 3) In Embodiment 1, Embodiment 2
24% by mass of polyethylene resin was prepared in the same manner as in Example 1 except that the extraction and removal of the mineral oil was performed such that a larger amount of the mineral oil was left in the film.
A microporous film having a thickness of 100 μm and comprising 56% by mass of silica powder and 20% by mass of mineral oil was obtained.
By the same method as described above, permeability to the electrolytic solution was imparted to obtain a capacitor separator.

(Comparative Example) 90 parts of a high-density polyethylene resin having a weight average molecular weight of 200,000 and 10 parts of diatomaceous earth having a specific surface area of 30 m ² / g were mixed and extruded from a T-die while being heated and melted and kneaded by an extruder. , Pressure molding with a molding roll,
Further, the film is stretched using a film stretching device to a thickness of 10
A 0 μm porous film was obtained. Next, this film was treated with an ethanol solution containing 0.5% by mass of dialkylsulfosuccinic acid sodium salt to impart permeability to an electrolytic solution to obtain a capacitor separator.

[0019]

[Table 1]

From the results shown in Table 1, according to the separators of Examples 1 to 3, the porosity of the separator can be adjusted to an arbitrary value simply by adjusting the amount of the mineral oil remaining in the pores of the separator to a predetermined amount. It was confirmed that a separator having desired electrical resistance could be easily obtained. Moreover, since the pores were filled with silica powder having a large specific surface area, the result was that the separator of the comparative example was excellent in retaining the permeability of the electrolytic solution. Further, despite containing a large amount of silica powder, there is no problem such as material dropping during capacitor assembly, and a separator having an average pore diameter of 0.1 μm or less and excellent in short circuit resistance. was gotten.

[0021]

The electric double layer capacitor separator of the present invention is obtained by extruding a raw material composition obtained by mixing a polyolefin resin, an inorganic powder and an oily material into a film,
By extracting and removing the oily substance using an appropriate extractant so that a predetermined amount of the oily substance remains in the film, the porosity can be easily and arbitrarily adjusted, so that an arbitrary electric resistance value can be obtained. It is possible to easily obtain the capacitor separator that it has, and its industrial utility value is high. Moreover, the separator has a small average pore diameter of 0.1 μm or less, which is excellent in short-circuit resistance. Further, since the pores are filled with silica powder having a large specific surface area, the electrolytic solution has a high holding power, so that the electrolytic Since the effect of suppressing the liquid dryout phenomenon is great, it can contribute to the extension of the life of the capacitor.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Taizo Matsunami             630 Tarui-cho, Fuwa-gun, Gifu Japan Inorganic Stock Association             Inside the company Tarui factory (72) Inventor Taku Takashi             630 Tarui-cho, Fuwa-gun, Gifu Japan Inorganic Stock Association             Inside the company Tarui factory

Claims (6)

[Claims] 1. A microporous separator for a capacitor using an aqueous or non-aqueous electrolyte, wherein the constituent material of the separator is a polyolefin resin and inorganic powder, and a part of the pores of the separator. A separator for capacitors, characterized in that an oily substance that is insoluble in the electrolyte is left behind and adjusted to a predetermined electric resistance value. 2. The capacitor according to claim 1, wherein the oily substance insoluble in the electrolytic solution is one kind or a mixture of two or more kinds selected from paraffin type or naphthene type hydrocarbon compounds. Separator. 3. The average pore diameter measured by mercury porosimetry is 0.1 μm.
The separator for capacitors according to claim 1 or 2, wherein the separator is m or less. 4. The polyolefin resin contains ultra high molecular weight polyethylene having a weight average molecular weight of 500,000 or more, and the inorganic powder is mainly composed of silica. The separator for capacitors according to any one of 1. 5. The composition ratio (mass ratio) of the polyolefin resin and the inorganic powder is set to 2: 8 to 8: 2, more preferably 2: 8 to 5: 5. 5. The capacitor separator according to any one of 4 to 4. 6. A microporous separator for capacitors using an aqueous or non-aqueous electrolyte, wherein the constituent material of the separator is a polyolefin resin and inorganic powder, and This is a method of manufacturing a capacitor separator in which an oily substance that is insoluble in the electrolytic solution remains in part and is adjusted to a predetermined electrical resistance value. A film is produced from the mixed raw material composition by an extrusion method, and then the oily substance is extracted and removed from the film by using an extractant, so that a predetermined amount of the oily substance is left in the separator to have a porosity. A method for manufacturing a capacitor separator, wherein the method is adjusted.