JPH0334845B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an aluminum electrolytic capacitor, and particularly to an electrolytic capacitor using an electrolytic solution that can prevent corrosion of an anode foil and lead tab portion due to cleaning with a halogen-based organic solvent. [Prior art and problems to be solved by the invention] In general, electrolytic capacitors are made by etching a high-purity aluminum foil and anodizing the surface of the anode foil, and an etched aluminum cathode foil facing the anode foil. The device is constructed by impregnating an element with an electrolytic solution in a wound structure with a separator paper interposed therebetween, and then housing this element in an aluminum case and sealing it with an elastic sealing body. In recent years, electrolytic capacitors are mounted on printed circuit boards, and after soldering, the boards are cleaned using halogen-based organic solvents such as 1,1,1-trichloroethane and trichlorotrifluoroethane to remove solder flux. There is. By the way, the halogen-based organic solvent diffuses through the sealing body of the electrolytic capacitor, causing dissociation of chlorine ions in the electrolyte inside the capacitor. These dissociated chlorine ions cause corrosion of the anode foil and lead tab portion of the electrolytic capacitor during use, resulting in a defect in the electrolytic capacitor. Conventionally, therefore, a method has been implemented in which a resin is applied to the surface of the elastic sealing body to impart corrosion resistance. However, this method does not meet the demands for miniaturization and cost reduction. It is also known that corrosion inhibitors such as P-nitrophenol and P-nitrobenzoic acid are added to the electrolyte to improve its corrosion resistance against halogenated organic solvents, but sufficient corrosion resistance is not sufficient. 1,
Almost no corrosion resistance was obtained when cleaning with 1,1-trichloroethane. Generally, corrosion of aluminum by chlorine ions is expressed by the following formula [Al ³⁺ +3Cl ^- →Alcl ₃ ], and the corrosion growth process can be divided into two stages. In the first step, chloride ions directly react with the aluminum metal surface to form Alcl ₃ . This first step is a competitive reaction with aluminum passivation, so the reaction rate is slow.
The next second step is the Alcl ₃ produced in the first step.
As the concentration of AlCl 3 increases, AlCl ₃ acts as a catalyst, activating the aluminum metal surface and easily eluting Al ³⁺ from the aluminum metal surface, making it easier to react with chlorine ions and causing rapid corrosion. proceed. The reaction rate of this second stage is much faster than that of the first stage. Therefore, the present inventors discovered that ethylenediaminetetraacetic acid or a salt thereof, which is used as a sequestering agent, is effective in the second stage of corrosion.
It has been found that it has the effect of suppressing the elution of Al ³⁺ and can prevent corrosion. [Object of the Invention] The present invention has been made in view of these circumstances, and is an effective method for cleaning electrolytic capacitor substrates using halogenated organic solvents such as 1,1,1-trichloroethane and trichlorotrifluoroethane. It is an object of the present invention to provide an electrolytic capacitor which has sufficient corrosion resistance to the liquid and can prevent corrosion of the anode foil and the lead tab portion. [Means for Solving the Problems and Their Effects] In order to achieve the above object, the electrolytic capacitor according to the present invention contains ethylene diamine in an electrolytic solution containing ethylene glycol as the main solvent and adipic acid or a salt thereof as the main electrolyte. Tetraacetic acid or its salt is added and dissolved. In this electrolytic capacitor, in the second stage of corrosion, it is possible to suppress the elution of Al ³⁺ from the aluminum metal surface and prevent corrosion of the anode foil and the lead tab portion. [Embodiments of the Invention] Examples of the electrolytic capacitor according to the present invention will be described below. The embodiments are described for generally wound aluminum electrolytic capacitors. The electrolytic capacitor used in the examples is made by electrochemically etching aluminum foil, anodizing it in an aqueous phosphate solution to form an oxide film on the surface, and then attaching a lead tab for electrode extraction to the aluminum anode foil. form. On the other hand, after etching the aluminum foil, a lead tab for drawing out the electrode is attached to create an aluminum cathode foil, and a separator paper is overlapped and wound between the anode foil and the cathode foil to form a capacitor element. To manufacture. Then, this capacitor element is impregnated with an electrolytic solution and housed in, for example, a bottomed aluminum case, and the opening of the case is sealed with an elastic sealing member. Table 1 shows that using ethylene glycol as the main solvent,
The compositions of conventional examples in which aluminum adipate is dissolved as the main electrolyte, and examples of the present invention using electrolytic solutions in which 0.1 and 3.0 wt% of ethylenediaminetetraacetic acid are added and dissolved in these conventional examples are shown.

【table】

[Table] 50WV-
We prototyped a 10μF electrolytic capacitor. This test capacitor was subjected to ultrasonic cleaning at 28 KHz for 5 minutes using two solvents, 1,1,1-trichloroethane and trichlorotrifluoroethane. Afterwards, a high-temperature load test was conducted at 150°C with a rated voltage applied, and after 500 and 1000 hours, it was dismantled and the corrosion incidence rate (number of corrosion occurrences/number of tests) was investigated. The results are shown in Table-2.

〔Effect of the invention〕

As explained above, according to the present invention, 1, 1,
When cleaning electrolytic capacitor substrates with halogen-based organic solvents such as 1-trichloroethane and trichlorotrifluoroethane, it can provide sufficient corrosion resistance to the electrolytic solution and prevent corrosion of the anode foil and pull-out lead tabs. effective.

Claims (1)

[Scope of Claims] 1. An aluminum electrolytic capacitor characterized in that ethylenediaminetetraacetic acid or its salt is added to an electrolytic solution containing ethylene glycol as the main solvent and adipic acid or its salt as the main electrolyte. capacitor. 2. The electrolytic capacitor according to claim 1, wherein the amount of the ethylenediaminetetraacetic acid or its salt added is 0.1 to 10 wt%.