JPH06151249A - Separator for capacitor and capacitor using thereof - Google Patents

Abstract

PURPOSE:To obtain a separator for capacitor, which has an affinity and has a stable heat resistance for a long period, by a method wherein a coating layer containing a fluorine surface active agent having a specified structure is chemically made to apply on the surfaces of small holes in a fluorine high-molecular polymer porous film. CONSTITUTION:A coating layer containing a fluorine surface active agent having a structure, which is shown by a formula I, is formed on the surfaces of small holes in a fluorine high-molecular polymer film, desirably a PTFE porous film, by a chemical affinity. In the formula I, the R is H, OH, COOH or CH3, the (m) is 1 to 17 and the (n) is 1 to 20. As the surface active agent, a surface active agent with an ethylene oxide part, which is substituted for an OH group or a COOH group in its one group, is specially desirable. Thereby, a separator for capacitor, which is capable of absorbing and holding an electrolyte, has an oxidation resistance and an alkali resistance and is stable even at a high temperature, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator suitable for capacitors, an electrolytic capacitor and an electric double layer capacitor using the same, and more specifically, it has sufficient hydrophilicity and long-term stable heat resistance. The present invention relates to a separator for an electrolytic capacitor or an electric double layer capacitor that has.

[0002]

2. Description of the Related Art Conventionally, as a separator for capacitors, kraft paper, Manila paper, and a porous film of polyethylene or polypropylene which has been subjected to a treatment such as grafting with a hydrophilic monomer have been used. Also, a porous membrane obtained by treating a fluororesin with alcohol (Japanese Patent Laid-Open No. 62-263624) and a fluororesin porous membrane formed by coating a substance having an affinity for a polar organic solvent (Japanese Laid-Open Patent Publication No. 2-241013) , A fluororesin porous film formed by sputter etching (JP-A-3
-171612) and the like have been proposed.

[0003]

However, kraft paper and manila paper have the problem that they cannot be used because they are deteriorated by being exposed to high temperatures in an electrolytic solution and become brittle in an acidic electrolytic solution such as sulfuric acid. It was Also, in the case of polyethylene or polypropylene porous film, there is concern about the heat resistance, and when used for a long time at high temperature, or when heated for a short time of 200 ° C or more during the capacitor manufacturing process, it melts and the pores are blocked. was there. Further, in the case of a porous membrane obtained by treating a fluororesin with alcohol, there is a problem that the membrane is dried and the amount of the absorbing liquid is reduced after long-term use.

Further, in the case of a fluororesin porous film formed by sputter etching, only the surface is modified to be hydrophilic, and the inside (thickness direction) of the film is not treated. When used, there was a problem that the amount of absorbing liquid in the separator was reduced and the performance of the capacitor was reduced. Further, in the case of a fluororesin porous membrane formed by coating a specific perfluoro ion exchange polymer as a substance having an affinity for a polar organic solvent, this polymer has one --CF ₃ end that is a hydrophobic portion, The affinity for the polymer was weak and the polymer could not be sufficiently hydrophilicized by the polymer, and the obtained separator was not satisfactory.

[0005]

The present invention has been made to solve the problems of the prior art, and has a specific structure to be described later, at least on the surface of the pores of the fluoropolymer macromolecular porous film. By chemically coating the fluorine-containing surfactant having a hydrophilic property, the hydrophobic film can retain sufficient hydrophilicity without being crosslinked, and it has sufficient hydrophilicity and is stable for a long period of time. It is possible to obtain a heat-resistant capacitor separator.

That is, the present invention provides the following [Chemical formula 2] on at least the surface of the pores of the fluoropolymer macromolecular film.

[Chemical 2] (In the above formula, R is H, OH, COOH, or CH ₃ , m
Is 1 to 17, and n is 1 to 20. The coating layer of a fluorosurfactant having a structure represented by (4) is formed by chemical affinity to provide a hydrophilic separator for capacitors.

Further, the present invention relates to a capacitor having a separator impregnated with an electrolytic solution and arranged between a pair of electrodes.

The fluoropolymer porous film used in the present invention is made of PTFE or polyvinylidene fluoride (PVd).
F), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FE
P), tetrafluoroethylene-ethylene copolymer (E
TFE), polychlorotrifluoroethylene (CTF)
It is a hydrophobic film made of E) or the like, and PTFE is particularly preferable from the viewpoint of chemical resistance, heat resistance and the like. Also 0.01 to 20 μm
Especially, a membrane having a pore size of 0.05 to 5 μm is preferably used.

The fluorosurfactant as the coating layer in the present invention has a structure represented by the above [Chemical formula 2].
Particularly, the ethylene oxide part is partially OH group or CO
Surfactants substituted with OH groups are preferably used.
These fluorine-based surfactants are thermally stable and
There is also a structure having heat resistance of 0 ° C or higher and heat resistance of 250 ° C or higher. Furthermore, it has excellent alkali resistance and acid resistance.

Specific examples of such a fluorine-containing surfactant include, for example, the following [Chemical Formula 3]

[Chemical 3] What is represented by.

In the present invention, the coating layer of the above-mentioned fluorine-containing surfactant is formed on at least the surface of the pores of the above-mentioned fluorine-containing high molecular polymer porous film by chemical affinity. The term "pore surface" as used herein means a fiber surface that constitutes porosity, and the coating layer may be formed at least on the pore surface, that is, in the thickness direction. May be formed on the surface of.

The method for coating the surface of the fine pores of the fluorine-containing high molecular polymer porous membrane with the above-mentioned fluorine-containing surfactant is not particularly limited. 1-10% by weight of solvent, preferably 1-
After being diluted to 5% by weight, the fluoropolymer high molecular weight polymer porous membrane can be coated by a method such as immersing it in the solution, or coating the solution and drying the membrane, thus making it hydrophilic. A hydrophobic membrane can be easily obtained. The organic solvent used here is not particularly limited, but for example, acetone, ethanol, isopropyl alcohol, etc. are preferably used.

Here, the coating amount of the fluorine-based surfactant can be appropriately controlled by the concentration of the fluorine-based surfactant, the dipping time and the coating amount. In the present invention, the weight ratio after coating / before coating is 1.040 / 1. ~ 1.070 / 1 is preferable, and especially 1.045 / 1 ~
1.060 / 1 is preferable. If it is less than 1.040, satisfactory hydrophilicity may not be obtained in some cases, and if it is more than 1.070, the amount dropped off after coating may be large and the capacitor characteristics may be deteriorated.

Further, in the present invention, as the pretreatment and / or posttreatment of the above-mentioned coating treatment, the porous film is treated with plasma (H ₂ , O ₂ , Ar, N ₂ , CO ₂ , Air, H ₂ O). etc)
Irradiation, excimer laser irradiation, low pressure mercury lamp irradiation, electron beam irradiation, radiation irradiation and the like can also be performed to make the surface of the porous membrane hydrophilic.

In the present invention, as described above, a hydrophilic surfactant can be obtained by adsorbing the fluorine-based surfactant on the surface of the pores of the hydrophobic membrane by chemical affinity.

Further, this separator can be impregnated with an electrolytic solution and placed between a pair of electrodes to obtain an electrolytic capacitor or an electric double layer capacitor. Here, in the case of an electrolytic capacitor, the electrolytic solution may be, for example, an electrolyte such as adipate or phthalate, ethylene glycol, γ-butyrolactone or dimethylformamide (DM).
Those included in the solvent such as F) are included. Anode foil and cathode foil are used as electrodes. Here, as the anode foil, a metal having a film forming ability such as aluminum or tantalum on which a dielectric film is formed by anodic oxidation or the like, and as the cathode foil, the same metal foil as the anode foil is used. . These foils increase surface area per volume,
Often used are those that have been etched.

In the case of an electric double layer capacitor, an aqueous solution system using an aqueous solution of sulfuric acid, an aqueous solution of potassium hydroxide or the like as an electrolyte solution, or an electrolyte such as an alkylammonium perchlorate is used in the form of γ-butyrolactone, dimethylformamide or dimethylfluphoxide. Sid, a non-aqueous solution system dissolved in an organic solvent such as propylene carbonate, and the like include activated carbon fiber cloth as an electrode, or activated carbon fiber cloth having a conductive layer formed on one surface thereof, but not limited thereto. Not done.

[0018]

INDUSTRIAL APPLICABILITY In the present invention, at least the surface of the pores of the hydrophobic membrane can be treated to be hydrophilic, so that the electrolyte solution can be sufficiently absorbed and retained, and it has oxidation resistance and alkali resistance, and even at high temperatures. It is possible to obtain a capacitor separator that is stable and can maintain performance for a long period of time.

[0019]

【Example】

Example 1 A polytetrafluoroethylene (PTFE) porous membrane (manufactured by Nitto Denko Corporation, trade name NTF1111, nominal pore size 0.1 μm) was used.
Fluorine-based surfactant having the structure of the following [Chemical Formula 4]

[0020]

[Chemical 4]

Dipped in 2.5 wt% acetone solution of 3
After 0 minutes, the film was taken out and air-dried to obtain a separator for electrolytic capacitors. Cut this separator into 10 cm ² and set it on the cartridge type filtration device.
The pressure was reduced to 5 mmHg to allow pure water to permeate, and the pure water permeation rate was measured to be 4.5 ml / cm ² / min. The pure water is filtered as it is for 10 liters per cm ^{2 of the} separator, and then the separator is once taken out and dried in a dryer at 60 ° C. for 15 minutes.
The water was removed for a minute. Then, it was set in the cartridge type filtration device again, and pure water was filtered under the same conditions as above. As a result, the pure water permeation rate did not change, and it was confirmed that the surface of the pores was well covered with the fluorinated surfactant. It was

ESCA analysis of the surface of the separator showed that F / C = 2.0 and O / C = 0.01 before coating, but after coating, F / C = 1.3 and O / C = 0.26. It was confirmed that the ratio of F decreased and O increased. The weight ratio of the coated / pre-separator is 1.
052/1 (mass of coated fluorosurfactant to PTFE porous membrane was 5.2%).

Example 2 The coated film obtained by the method of Example 1 was cut into a 20 cm square and held in the plasma irradiation apparatus at a distance of 5 cm from the electrode. After evacuating to 10 ^-5 torr, Ar gas was supplied at 40 cc (STP) / min, and the inside of the chamber was 5 × 10 5.
^While maintaining at ^-2 torr, plasma was generated at an output of 13.56 MH ₂ and 50 W, and after discharging for 30 seconds, the film was taken out to obtain a capacitor separator.

Example 3 The PTFE porous membrane used in Example 1 was irradiated with plasma under the same conditions as in Example 2, and then coated with a fluorine-containing surfactant in the same manner as in Example 1 to give a capacitor. A separator for use was obtained.

Comparative Example 1 The initial pure water permeation rate of the capacitor separator obtained in the same manner as in Example 1 except that it was not treated with a fluorine-containing surfactant was not measurable because pure water did not permeate. It was Moreover, according to ESCA analysis, other elements were not observed except that F showed twice the strength of C.

Comparative Example 2 Fluorine-based surfactant having the structure of the following [Chemical formula 5]

[0027]

[Chemical 5]

A separator for capacitors was obtained in the same manner as in Example 1 except that was used. Pure water permeated initially in this separator, but when 0.3 liter of pure water per cm ^{2 of} the membrane was permeated and then dried, the separator returned to hydrophobic and pure water did not permeate.

The separators obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were impregnated with an electrolytic solution (electrolyte: ammonium adipate, solvent: γ-butyrolactone) to form a space between the aluminum anode foil and the aluminum cathode foil. Place it in
An aluminum electrolytic capacitor was obtained. Comparative Example 1
The separator obtained in 1. was moistened once with ethanol and then replaced with the electrolytic solution.

Such an electrolytic capacitor is rated at 200 V, 30
Table 1 shows the tangent value of the initial loss angle of 0 μF and the tangent value of the loss angle after 3000 hours at 120 ° C. As is clear from this, it is understood that the electrolytic capacitor separator of the present invention exhibits stable performance even after a long-term test at high temperature.

[0031]

[Table 1]

The separators obtained in Example 1 and Comparative Examples 1 and 2 were impregnated with an electrolytic solution (electrolyte: phthalic acid, solvent: γ-butyrolactone) and sandwiched between electrodes made of activated carbon fiber to form an electric double layer capacitor. Formed. The separator obtained in Comparative Example 1 was once moistened with ethanol and then replaced with the electrolytic solution.

Rating 5 of such an electric double layer capacitor
Table 2 shows the tangent values of the initial loss angle of V and 0.1 F and the tangent values of the loss angle after 3000 hours at 120 ° C. As is apparent from this, also in the electric double layer capacitor, the capacitor separator of the present invention shows stable performance even after a long-term test at high temperature.

[0034]

[Table 2]

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[Procedure amendment]

[Submission date] January 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

Specific examples of such a fluorine-containing surfactant include, for example, the following [Chemical Formula 3]

[Chemical 3] What is represented by.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

[0020]

[Chemical 4]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031]

[Table 1]

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

The separators obtained in Example 1 and Comparative Examples 1 and 2 were impregnated with an electrolytic solution (electrolyte: phthalic acid, solvent: γ-butyrolactone), and sandwiched between electrodes made of activated carbon fiber to form an electric double layer capacitor. Formed. The separator obtained in Comparative Example 1 was once moistened with ethanol and then replaced with the electrolytic solution.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

Rating 5 of such an electric double layer capacitor
Table 2 shows the tangent values of the initial loss angle of V and 0.1 F and the tangent values of the loss angle after 3000 hours at 120 ° C. As is apparent from this, also in the electric double layer capacitor, the capacitor separator of the present invention shows stable performance even after a long-term test at high temperature.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

[0034]

[Table 2]

Claims (2)

[Claims] 1. The following [Chemical formula 1] [Chemical formula 1] on at least the surface of the pores of the fluoropolymer macromolecular film. (In the above formula, R is H, OH, COOH, or CH ₃ , m
Is 1 to 17, and n is 1 to 20. A separator for a capacitor, characterized in that the coating layer of a fluorine-based surfactant having a structure represented by (4) is formed by chemical affinity and has hydrophilicity. 2. A capacitor comprising the separator according to claim 1 impregnated with an electrolytic solution and arranged between a pair of electrodes.