JP2010219083A - Electrolytic capacitor cathode foil and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode foil and a method of manufacturing the same, which suppresses resolution of an electrolytic capacitor cathode foil in an electrolyte, suppresses degradation of capacitance, and exhibits excellent waterproofness. <P>SOLUTION: The electrolytic capacitor cathode foil and a method of manufacturing the same are provided, wherein the electrolytic capacitor cathode foil is formed by carrying out immersion treatment for immersing a roughened etching foil in a solution containing molybdate such as sodium molybdate and phosphoric acid to form a film containing molybdenum and phosphorus on a surface of the etching foil. In the method of manufacturing the electrolytic capacitor cathode foil, an immersion treatment temperature is 25-70°C, and concentration of sodium molybdate in immersion treatment liquid is 0.05-0.25 wt.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cathode foil for electrolytic capacitors and a method thereof.

In recent years, while the electrolytic capacitor is required to have a low impedance, the electrolytic solution used in the low impedance product has a structure containing a large amount of water.
In an electrolyte containing a large amount of water, the aluminum cathode foil not only deteriorates due to a hydration reaction, but also due to the dissolution reaction of aluminum by the activation of the complexing reaction of various organic acids added as a solute. Deterioration is promoted. Therefore, the cathode foil for electrolytic capacitors used for low impedance products is required to have excellent water resistance and stability against complexing reaction.

  When the deterioration of the electrode foil is promoted, the electrolytic capacitor has a problem that the safety valve is opened due to a decrease in electrostatic capacity, deterioration of leakage current characteristics, and hydrogen gas generated by a dissolution reaction. . In particular, since the cathode foil is not covered with a thick oxide film unlike the anode foil, a dissolution reaction in the electrolytic solution easily occurs.

  Conventionally, it is well known that when an immersion treatment or a chemical conversion treatment is performed on a cathode foil with an aqueous phosphoric acid solution, the electrode foil has such an effect of preventing deterioration. (For example, see Non-Patent Document 1 and Patent Document 1)

JP-A-11-162791

Isaya Nagata, “Electrolytic Cathode Aluminum Electrolytic Capacitor”, Nippon Electric Storage Industrial Co., Ltd., February 24, 1997, P339-341

  However, the electrolyte used in current low-impedance products is an electrolyte that contains more water than the conventional electrolyte, and the conventional immersion treatment with phosphoric acid cannot achieve a sufficient effect. There is a need for a treatment that can further suppress the dissolution reaction.

  In addition, the method of increasing water resistance by chemical conversion treatment with a phosphoric acid aqueous solution or the method of immersing by increasing the phosphoric acid concentration of the phosphoric acid aqueous solution improves the water resistance, but greatly reduces the capacitance. Therefore, there has been a demand for a process capable of suppressing the dissolution reaction without reducing the capacitance, and a cathode foil by the process.

  In order to solve the above-mentioned problems, the present invention provides a cathode foil for an electrolytic capacitor, which is a film containing molybdenum and phosphorus (molybdic acid or molybdate, phosphoric acid or phosphate in the form of a roughened etching foil. A cathode foil for an electrolytic capacitor, characterized in that a coating film is formed.

  Further, in the method for producing a cathode foil for an electrolytic capacitor, a roughened etching foil is immersed in an aqueous solution containing molybdate and phosphoric acid to form a film containing molybdenum and phosphorus on the surface of the etching foil. This is a method for producing a cathode foil for an electrolytic capacitor.

  Furthermore, it is a manufacturing method of the cathode foil for electrolytic capacitors characterized by using sodium molybdate as the molybdate.

  And in the manufacturing method of the cathode foil for electrolytic capacitors, the immersion treatment temperature is 25-70 degreeC, It is a manufacturing method of the cathode foil for electrolytic capacitors characterized by the above-mentioned.

  Moreover, it is a manufacturing method of the cathode foil for electrolytic capacitors characterized by the sodium molybdate density | concentration in the said immersion treatment liquid being 0.05-0.25 wt%.

  In the present invention, the roughened etching foil is immersed in an aqueous solution containing molybdate and phosphoric acid to form an oxide film containing molybdenum and phosphorous, thereby dissolving the cathode foil in the electrolytic solution. It is possible to obtain a highly reliable cathode foil for electrolytic capacitors that is excellent in water resistance while suppressing the decrease in capacitance. The reason for this is not necessarily clear, but it is thought that the oxide film containing molybdenum with corrosion resistance and phosphorus that is effective in water resistance suppresses dissolution of the cathode foil film in the electrolyte due to the synergistic effect of both. It is done.

  Hereinafter, the present invention will be specifically described based on examples.

[Examples 1 to 5] Comparison of immersion treatment temperature By a known method, etching (roughening) treatment was performed on the aluminum original foil to prepare an etching foil sample. After the etching treatment, it was immersed in a phosphoric acid solution at 45 ° C. and 0.5 wt% to remove residual chlorine ions. Next, as shown in Table 1, an aqueous solution containing 0.15 wt% sodium molybdate and 0.10 wt% phosphoric acid was set at a temperature of 20, 25, 50, 70, 80 ° C., and after immersion treatment in the aqueous solution, Heat treatment was performed at 400 ° C. to prepare a cathode foil sample on which a film containing molybdenum and phosphorus was formed.

[Examples 6-11, 3] Comparison of sodium molybdate aqueous solution concentrations Etch foil samples were prepared in the same manner as in the above examples, and residual chlorine ions were removed after the etching treatment. Next, as shown in Table 1, the sodium molybdate concentration was 0.03, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 wt%, and phosphoric acid 0.10 wt%. The aqueous solution containing was set to 50 ° C., immersed in the aqueous solution, and then heat treated at 400 ° C. to prepare a cathode foil sample on which an oxide film containing molybdenum and phosphorus was formed.

(Comparative Examples 1 and 2) Comparison with an aqueous solution of sodium molybdate alone (no phosphoric acid) In the same manner as in the above example, an etching foil sample was prepared, and after the etching treatment, residual chlorine ions were removed. Next, as shown in Table 1, a sodium molybdate concentration was set to 0.15 wt%, an aqueous solution not containing phosphoric acid was set to 50 and 70 ° C., immersed in the aqueous solution, and then heat treated at 400 ° C. A cathode foil sample on which a film containing only the carbon was formed.

(Conventional example) Comparison with phosphoric acid alone (no sodium molybdate) aqueous solution In the same manner as in the above example, an etching foil sample was prepared, and after the etching treatment, residual chlorine ions were removed. Next, as shown in Table 1, the phosphoric acid concentration was set to 0.10 wt%, an aqueous solution not containing sodium molybdate was set to 50 ° C., and after immersion treatment in the aqueous solution, heat treatment was performed at 400 ° C., and phosphoric acid only A cathode foil sample on which an oxide film was formed was prepared.

  The cathode foil samples according to Examples 1 to 11 and Comparative Examples 1 and 2 and the conventional example were measured for film withstand voltage and capacitance, and then in an electrolytic solution of ethylene glycol 40 wt%, water 50 wt%, and ammonium adipate 10 wt%. The film was immersed for 8 hours at 105 ° C., and the rate of change in the film pressure resistance after the immersion was examined. The results are shown in Table 1.

As is clear from Table 1, Examples 1 to 11 immersed in an aqueous solution containing sodium molybdate and phosphoric acid had a change in capacitance and film withstand voltage as compared with the conventional example immersed in an aqueous solution containing only phosphoric acid. In particular, Examples 2 to 4 and 7 to 10 having an immersion treatment temperature of 25 to 70 ° C. and a sodium molybdate concentration of 0.05 to 0.25 wt% are particularly excellent.
Moreover, since Comparative Examples 1 and 2 immersed in an aqueous solution containing only sodium molybdate without containing phosphoric acid had a lower rate of change in capacitance and film pressure resistance than Examples 1-11, It can be seen that the combined use of phosphoric acid and sodium molybdate is essential.

In the above examples, sodium molybdate was used as the compound containing molybdenum, but other than these, alkali metal salts such as potassium and lithium, and ammonium salts can also be used.
Moreover, the heat processing temperature after an immersion process should just be 350-550 degreeC.

Claims (5)

In the cathode foil for electrolytic capacitors,
A cathode foil for an electrolytic capacitor, characterized in that a film containing molybdenum and phosphorus is formed on the surface of a roughened etching foil. In the method for producing a cathode foil for an electrolytic capacitor,
A cathode foil for an electrolytic capacitor, characterized in that a roughened etching foil is immersed in an aqueous solution containing molybdate and phosphoric acid to form a film containing molybdenum and phosphorus on the surface of the etching foil. Production method.   The method for manufacturing a cathode foil for an electrolytic capacitor according to claim 2, wherein sodium molybdate is used as the molybdate. In the manufacturing method of the cathode foil for electrolytic capacitors,
The method for producing a cathode foil for an electrolytic capacitor according to claim 3, wherein the immersion treatment temperature is 25 to 70 ° C. The method for producing a cathode foil for an electrolytic capacitor according to claim 3 or 4, wherein a concentration of sodium molybdate in the immersion treatment liquid is 0.05 to 0.25 wt%.