JPH0845788A - Capacitor - Google Patents

Abstract

(57) [Abstract] [Object] The present invention provides a capacitor using a separator suitable for capacitors, and more specifically, an electrolytic capacitor in which a separator having sufficient hydrophilicity and long-term stable heat resistance is arranged. And to provide electric double layer capacitors. A capacitor having a separator impregnated with an electrolytic solution disposed between a pair of electrodes, wherein the separator has infrared absorption derived from a C—O bond at a wave number of 1000 to 1200 cm ^−1. , And F by X-ray photoelectron spectroscopy
A hydrophilic porous fluororesin film having a / C value of 0.1 to 1.5 and an O / C value of 0.1 to 1.0 is used.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a separator for capacitors, kraft paper, manila paper, and a polyethylene or polypropylene porous film which has been subjected to a treatment such as grafting with a hydrophilic monomer are 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 by hydrophilization, 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 as a separator for a capacitor, a specific hydrophilic porous fluororesin film subjected to photochemical treatment is used. That is, not only on the surface of the porous fluororesin film, but also on the internal tissue surface, by using a film in which a hydrophilic group is introduced by a photochemical reaction using a specific compound described below, it is possible to obtain a hydrophobic porous fluororesin film having sufficient hydrophobicity. It is possible to provide a capacitor that is imparted with hydrophilicity, is stable to various electrolytic solutions, and can withstand use at high temperatures for a long time.

That is, the present invention is a capacitor having a separator impregnated with an electrolytic solution between a pair of electrodes, wherein the separator has a wave number of 1000 to 1200 cm.
^-1 has an infrared absorption derived from a C-O bond, and has an F / C value of 0.1 by X-ray photoelectron spectroscopy (referred to as XPS method).
To 1.5 and an O / C value of 0.1 to 1.0, the present invention relates to a capacitor characterized by using a hydrophilic porous fluororesin film, and the hydrophilic porous fluororesin film is a porous fluororesin film. It is preferable to use a film obtained by irradiating with ultraviolet rays in a state where an atom having a binding energy with a fluorine atom of 539 kJ / mol or more and a compound having a hydrophilic group are in contact with each other.

The porous fluororesin film in the present invention is made of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PF).
A), a hydrophobic film composed of tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (CTFE), etc., and particularly chemical resistance In terms of heat resistance and the like, PTFE is preferable, and either a baked product or an unbaked product can be used. Also 0.01-2
A film having a pore size of 0 μm, particularly 0.05 to 5 μm is preferably used. The porous fluororesin film can be obtained by various methods. For example, PTFE films are disclosed in Japanese Patent Publication No. 58-25332 and Japanese Patent Publication No. 51-18.
It can be obtained by a stretching method described in Japanese Patent Publication No. 991, Japanese Patent Publication No. 42-13560, etc., or a method using a foaming agent described in Japanese Patent Publication No. 42-4974, etc.

These porous fluororesin films are essentially C except for PFA before the photochemical treatment according to the present invention.
No infrared absorption due to —O bond was observed, while XPS
Approximate F / C and O / C values by the method are PT
FE (2.0, 0), PVdF (1.0, 0), PFA (2.0,
0.2 or less), FEP (2.0, 0), ETFE (1.0, 0),
It has CTFE (1.5,0). The photochemical treatment preferable in the present invention is such that the above porous fluororesin film has a binding energy of 539 kJ / mol with a fluorine atom.
Ultraviolet rays are radiated in a state where the above-mentioned atom and the compound having a hydrophilic group are in contact with each other, and C is applied at a wave number of 1000 to 1200 cm ^-1 .
Has infrared absorption derived from —O bond, and has F / C value of 0.1 to 1.5 and O / C value of 0.1 to 1.0 by XPS method.
Of the hydrophilic porous fluororesin film.
Processing operations are usually depending on the compound used, the ultraviolet rays having a wavelength of 150~270nm 6J / cm ² or more, and it is preferably irradiated at an energy intensity of 6~500J / cm ^2.

The compound used in the present invention is a compound having an atom having a binding energy with a fluorine atom of 539 kJ / mol or more and a hydrophilic group, and the electronegativity of the atom is 2.5.
Preferably there are: These compounds include:
Aluminum (bonding energy with fluorine atom: 671
kJ / mol, electronegativity: 1.5), boron (745
kJ / mol, 2.0), calcium (560 kJ / m)
ol, 1.0), barium (581 kJ / mol, 1.
2), having an atomic group such as lithium (580 kJ / mol, 1.0), hydrogen (566 kJ / mol, 2.1) and a hydrophilic group, for example, aluminum hydroxide, boric acid, ammonium borate, lithium hydroxide, water. Compounds such as calcium oxide, barium hydroxide, aluminum ethoxide, formic acid and acetic acid can be used. In the present invention, an aqueous solution of these compounds is preferably used, and an aqueous solution of an aluminum compound, a boron compound or a lithium compound having a hydrophilic group is particularly preferable. Further, an alkali salt such as sodium hydroxide or potassium hydroxide may be added to increase the solubility of the solute.

In the present invention, the compound is irradiated with ultraviolet rays in a state of being brought into contact with the porous fluororesin film, but it may be impregnated with an aqueous solution of the compound so as to penetrate the surface of the porous internal tissue. Good contact. In addition, since the porous fluororesin film itself is hydrophobic, plasma (H ₂ , O ₂ , Ar, CO ₂ , A) is used as a pretreatment for performing the above impregnation and coating steps more smoothly.
Ir, H ₂ O, etc.), an excimer laser, a low-pressure mercury lamp, an electron beam, radiation, an excimer lamp, or the like may be applied to make the surface of the porous fluororesin film hydrophilic.

As the ultraviolet light source, the C--F bond (53
9 kJ / mol) may be cut with one photon or with a small amount of two photons, and the photon energy for cutting the C—F bond preferably has a wavelength of 270 nm or less. However, if the wavelength is too short, light is strongly absorbed by the fluororesin film, so that sufficient energy for causing a photochemical reaction is difficult to reach in the film thickness direction.
Therefore, it is preferable that the ultraviolet rays have a wavelength of 150 to 270 nm. As the ultraviolet light source, a low-pressure mercury lamp, a high-pressure mercury lamp, a YAG laser (fourth harmonic), a metal halide lamp, an excimer lamp, or the like can be used. preferable.

By irradiating ultraviolet rays from such a light source, the C—F bond (539
cJ / mol) is cut. At this time, by allowing an atom having a bond energy with the fluorine atom of C—F bond (539 kJ / mol) or more to exist, the cleaved fluorine atom bonds with the atom and is trapped. The electronegativity of the fluorine atom is as large as 4.0, so that the presence of an atom smaller than the carbon atom (electronegativity: 2.5) causes CF.
It is possible to prevent reconnection between them. The bond energy between the atom and the fluorine atom is higher than that of the C—F bond, so that the bond is not easily broken again. Therefore, a part of the fluorine atoms of the porous fluororesin film can be replaced with the hydrophilic group.

By such hydrophilic treatment, C—O such as C—OH, C—COOH, and C—O—C is attached to the main chain, side chain or terminal of the polymer of the porous fluororesin on the surface of the separator pores.
Since a hydrophilic group having a bond is introduced, it is hydrophilic and has excellent alkali resistance and acid resistance. Here, the term "pore surface" means a surface that constitutes the porosity of the separator and an internal tissue surface, and the portion that is hydrophilized by the above hydrophilization treatment is not only the separator surface but also the internal tissue surface. It is characterized by being formed in.

The hydrophilic porous fluororesin film obtained by the above photochemical treatment has a wave number of 1 by infrared absorption method.
000 to 1200 cm ⁻¹ has an infrared absorption derived from a C—O bond, and has an F / C value of 0.1 to 10 in the XPS method.
The value of 1.5 and the O / C value are in the range of 0.1 to 1.0. F / C
If the value is smaller than 0.1 and the O / C value is larger than 1.0, the original properties of the fluororesin are lost, and if the F / C value is larger than 1.5 and the O / C value is smaller than 0.1, the hydrophilicity tends to be poor. Appears.

The capacitor of the present invention comprises a separator impregnated with an electrolytic solution disposed between a pair of electrodes, and the above-mentioned hydrophilized porous fluororesin film is used as the separator. It is assembled into capacitors and electric double layer capacitors. In the case of an electrolytic capacitor, as an electrolytic solution, for example, an electrolytic solution containing an electrolyte such as adipate or phthalate in a solvent such as ethylene glycol, γ-butyrolactone or dimethylformamide can be mentioned. Anode foil and cathode foil are used as electrodes. 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 are often etched so as to increase the surface area per volume.

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 perchlorate of alkylammonium is used as γ-butyrolactone, dimethylformamide, dimethylsulfoxide, A non-aqueous solution system dissolved in an organic solvent such as propylene carbonate may be used, and the electrode may be, for example, activated carbon fiber cloth or an activated carbon fiber cloth having a conductive layer formed on one surface thereof, but is not limited thereto.

[0017]

According to the present invention, as a separator for a capacitor, C--O at a wave number of 1000 to 1200 cm ^-1 is used.
It has an infrared absorption derived from a bond and has an F / C value of 0.1 to 1.5 and an O / C value of 0.1 to X determined by X-ray photoelectron spectroscopy.
A hydrophilic porous fluororesin film of 1.0 is used, and the preferred production method is a state in which a compound having a hydrophilic group and an atom having a binding energy with a fluorine atom of 539 kJ / mol or more is brought into contact with the porous fluororesin film. Obtained by irradiating ultraviolet rays. Therefore, not only the surface of the porous fluororesin film having strong hydrophobicity, but also the surface of the internal tissue has been subjected to a hydrophilic treatment, which can sufficiently absorb and retain the electrolytic solution, and also has oxidation resistance and alkali resistance, and even at high temperatures. It is possible to obtain a capacitor that is stable and can maintain its performance for a long time.

[0018]

The present invention will be specifically described below with reference to examples. To manufacture the capacitor separator of the present invention,
First, an aqueous solution of the compound is impregnated into the pores of a porous fluororesin film (including pretreatment such as plasma treatment). The porous fluororesin film may be impregnated with an organic solvent or subjected to ultrasonic cleaning in an organic solvent. The impregnation of the aqueous compound solution into the pores of the porous fluororesin film can be carried out by various methods, but the following method is preferable in consideration of the fact that this film is hydrophobic. (1) (a) The porous fluororesin film is immersed in an organic solvent (methanol, ethanol, acetone, isopropyl alcohol, etc.) having excellent compatibility with water and having a surface tension of 30 dyne / cm or less, and then immersed in the film. The first step of impregnating with a solvent, (b) then immersing it in water,
Second step of substituting with water (water is impregnated into pores),
(C) After that, the film is immersed in the compound solution, and water is replaced with the aqueous solution (the aqueous solution is impregnated into the pores).
The third step, a method of impregnating through the above three steps. (2) The compound is mixed with the above-mentioned low surface tension organic solvent to prepare a solution having a concentration of 30 dyne / cm or less, which is applied or sprayed on the porous fluororesin film, or the film is dipped to form a porous film. Method of impregnating a compound solution into the pores of a fluororesin film. When the compound solution is impregnated into the pores of the porous fluororesin film by the method as described above, and then irradiated with ultraviolet rays in the next step, some of the fluorine atoms of the fluororesin film are replaced with hydrophilic groups. . The irradiation time from the ultraviolet light source is set in consideration of various factors such as output, irradiation distance, type of compound solution, concentration, film shape, and thickness, but is usually 20 seconds to 30 minutes.

Example 1 Polytetrafluoroethylene (PTFE) porous film (manufactured by Nitto Denko Corporation, trade name NTF1121, nominal pore size of 0.
1 μm) was successively dipped in methanol and water for 10 minutes each, and further dipped in a 4.1% by weight boric acid aqueous solution for 10 minutes to impregnate the pores with the boric acid aqueous solution. This film has a low pressure mercury lamp with an output of 650 W (Oak Co., Ltd .; VU
After irradiating with V-65B-22-21, wavelength 185 nm, 254 nm) for 60 seconds, it was washed with pure water and air-dried to obtain a capacitor separator. Cut this separator into 10 cm ² ,
Set it on the cartridge type filtration device and set the permeation side to
The pressure was reduced to cmHg to allow pure water to permeate therethrough, and the pure water permeation rate was measured to be 5.2 ml / cm ² / min. In this state, pure water was filtered at a rate of 10 liters per cm ^{2 of the} separator, and then the separator was once taken out and placed in a dryer for 6
The water was removed at 0 ° C for 15 minutes. Then, it was set again in the cartridge type filtration device, and pure water was filtered under the same conditions as described above. As a result, it was confirmed that the pure water permeation rate did not change and the water was hydrophilized. Analysis of this separator by the XPS method showed that F / C = 2.0 and O / C = 0.0 before the treatment.
It was 1, but after processing F / C = 0.28, O / C =
It was 0.19, and it was confirmed that the ratio of F decreased and O increased. Also, when waveform analysis was performed, −
Assuming that the number of C atoms in the CF ₂ -bond (292 eV) is 100, the number of —C—O— bonds (286 eV) is 80, the number of —C═O bonds (288 eV) is 16, and a hydrophilic group may be present. confirmed. Prior to treatment, those functional groups were absent. In addition, an infrared absorption chart (FITS-40 manufactured by BIORAD) measured by a transmission method is shown in FIGS. 1 and 2. Figure 1 is an infrared absorption spectrum of the sample before the hydrophilization treatment, Figure 2 shows a difference spectrum obtained by subtracting the peak in FIG. 1 from the infrared absorption spectrum of the sample after hydrophilization, C wave number 1000 to 1200 ^-1 Infrared absorption derived from —O bond is observed. The separator obtained by the above treatment was impregnated with an electrolytic solution (electrolyte: ammonium adipate, solvent: γ-butyrolactone) and placed between an aluminum anode foil and an aluminum cathode foil to obtain an aluminum electrolytic capacitor. . Table 1 shows the tangent values of the initial loss angle of 200 V and 300 μF of this electrolytic capacitor and the tangent values of the loss angle after 3000 hours at 120 ° C. Similarly, the separator obtained by the above treatment was 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. Table 2 shows the values of the tangent of the initial loss angle of this electric double layer capacitor at a rating of 5 V and 0.1 F and the tangent of the loss angle after lapse of 3000 hours at 120 ° C.

Example 2 4% by weight of aluminum hydroxide was used instead of the boric acid aqueous solution.
A capacitor separator was obtained in the same manner as in Example 1 except that an aqueous solution containing 10% by weight of sodium hydroxide was used. The analysis result by XPS method shows F /
C = 0.37, O / C = 0.16, wave number 1000
Infrared absorption derived from the C—O bond was observed at ˜1200 cm ⁻¹ . Using this separator, an aluminum electrolytic capacitor and an electric double layer capacitor were prepared in the same manner as in Example 1, and the test results thereof are shown in Tables 1 and 2.

Example 3 The PTFE porous film used in Example 1 was held at a distance of 5 cm from the electrode in a plasma irradiation apparatus, and 10 ^-5 t was applied.
After evacuation to orr, Ar gas of 40 cc (ST
P) / min. 5 × 10 ^-2 t in the chamber
Plasma was generated at an output of 13.56 MHz and 50 W while kept at orr and discharged for 30 sec to pretreat the film. This film was hydrophilized in the same manner as in Example 1 to obtain a capacitor separator. The analysis result by the XPS method shows that F / C = 0.35 after the hydrophilic treatment,
O / C = 0.22, wave number 1000-1200 cm
Infrared absorption derived from the C—O bond was observed at ⁻¹ . Using this separator, an aluminum electrolytic capacitor was prepared in the same manner as in Example 1, and the test results are shown in Table 1.

Example 4 Instead of the low pressure mercury lamp, KrCl (wavelength 222n
m, 542 kJ / mol) Excimer lamp (20 W) was irradiated for 5 minutes to obtain a capacitor separator in the same manner as in Example 1. It was confirmed that this separator was made hydrophilic even after washing, filtering with pure water, and drying. XP
The analysis result by the S method shows that F / C = 0.3 after the hydrophilic treatment.
5, O / C = 0.22, wave number 1000-1200
Infrared absorption derived from the C—O bond was observed at cm ⁻¹ . Using this separator, an electric double layer capacitor was prepared in the same manner as in Example 1, and the test results are shown in Table 2.

Example 5 In Example 1, a polyvinylidene fluoride (PVdF) porous film (nominal pore size 0.2 μm, thickness 80 μm) was used instead of the PTFE porous film, and a 10 wt% formic acid aqueous solution was used instead of the boric acid aqueous solution. A separator for capacitors was obtained in the same manner as in Example 1 except that was used. The analysis result by XPS method shows that F / C = 1.0, O /
C = 0.01, but after hydrophilic treatment, F / C = 0.
35, O / C = 0.25, wave number 1000-12
Infrared absorption derived from the C—O bond was observed at 00 cm ⁻¹ . Using this separator, in the same manner as in Example 1,
An electric double layer capacitor was prepared, and the test results are shown in Table 2.

Comparative Example 1 A separator was obtained in the same manner as in Example 1 except that the aqueous solution of boric acid was impregnated, but irradiation with a low pressure mercury lamp was not performed. The initial pure water permeation rate of this separator could not be measured because pure water did not permeate. In addition, according to the XPS analysis, no other element was observed except that F showed twice the strength of C. For comparison, using this separator, an aluminum electrolytic capacitor and an electric double layer capacitor were prepared in the same manner as in Example 1, and the test results thereof are shown in Tables 1 and 2.

Comparative Example 2 The PTFE porous film used in Example 1 was dipped in a 2.5 wt% acetone solution of a fluorochemical surfactant (perfluoroalkylcarboxylic acid salt type) and air dried for 30 minutes to form a separator. Got Pure water initially permeated through this separator, but when 0.3 liter per 1 cm ² of pure water was permeated and then dried, it returned to hydrophobicity and stopped permeating pure water. For comparison, using this separator, Example 1
An aluminum electrolytic capacitor and an electric double layer capacitor were prepared in the same manner as in, and the test results are shown in Table 1 and Table 2.
It was shown to.

[0026]

[Table 1]

[0027]

[Table 2]

As is apparent from Tables 1 and 2, the capacitor of the present invention uses not only the surface of the porous fluororesin film having a strong hydrophobic property but also the film of which the internal tissue surface is hydrophilized as a separator. It can be seen that the liquid can be sufficiently absorbed and held, and stable performance is exhibited even after a long-term test at high temperature.

[0029]

[Brief description of drawings]

1 shows an infrared absorption spectrum of a PTFE porous film in Example 1 before a hydrophilic treatment.

FIG. 2 shows a difference spectrum obtained by subtracting the peak in FIG. 1 from the infrared absorption spectrum of the PTFE porous film in Example 1 after the hydrophilic treatment.

Claims (4)

[Claims] 1. A capacitor comprising a separator impregnated with an electrolytic solution between a pair of electrodes, wherein the separator has infrared absorption derived from a C—O bond at a wave number of 1000 to 1200 cm ^−1. And has an F / C value of 0.1 to 1.5 and an O / C value of 0.1 to 1. by X-ray photoelectron spectroscopy.
A capacitor characterized by using a hydrophilic porous fluororesin film of 0. 2. CO at a wave number of 1000 to 1200 cm ^-1
It has an infrared absorption derived from a bond and has an F / C value of 0.1 to 1.5 and an O / C value of 0.1 to X determined by X-ray photoelectron spectroscopy.
A hydrophilic porous fluororesin film of 1.0 has a binding energy of 53 with a fluorine atom in the porous fluororesin film.
The capacitor according to claim 1, which is obtained by irradiating with ultraviolet rays in a state where 9 kJ / mol or more atoms and a compound having a hydrophilic group are in contact with each other. 3. The capacitor according to claim 2, wherein the compound is an aluminum compound, a boron compound, a lithium compound, or a hydrogen compound. 4. The capacitor according to claim 2, wherein a light source having a wavelength of 150 to 270 nm as ultraviolet rays is used.