JPH0456444B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electrolytic solution used in electrolytic capacitors, and particularly to an electrolytic solution that has excellent resistance to corrosion caused by cleaning with a halogenated hydrocarbon cleaning agent and is effective in suppressing increases in internal pressure. Regarding electrolyte. [Prior Art] Electrolytic capacitors using liquid electrolytes are made of film-forming metals such as aluminum, tantalum,
A capacitor element with a structure in which niobium or the like is used for the anode side electrode, a dielectric oxide film is formed on the surface of this electrode by chemical conversion treatment, and the separator paper is interposed between the capacitor element and the cathode side electrode is placed opposite to the cathode side electrode is housed in an exterior case. It has a structure in which the opening is sealed with an elastic sealing body made of synthetic rubber or the like. In order to expand the surface area of the anode, the anode is usually etched to form fine irregularities, and the oxide film that serves as the dielectric is not formed along these irregularities, so it is possible to effectively extract capacitance. In order to achieve this, there must be a cathode with an uneven surface. The electrolytic solution is conductive and is held by the separator paper, interposed between the uneven surface of the dielectric oxide film and the cathode side electrode, and serves as a true cathode. The electrolyte also has the role of repairing missing or destroyed portions of the dielectric oxide film, and is an important component that determines various characteristics of the electrolytic capacitor. In recent years, most electrolytic capacitors are used by being attached to printed wiring boards, and after components are attached and soldered to printed wiring boards, the board is cleaned to remove solder flux. For this substrate cleaning, a halogenated hydrocarbon cleaning agent such as trichloroethane or trichlorotriflloethane is used. However, if this cleaning agent penetrates the gap between the sealing portion of the electrolytic capacitor or the elastic sealing body itself and enters the interior, and is liberated as chlorine ions in the electrolyte, the electrodes will corrode and the electrolytic capacitor will become defective. Furthermore, when the dielectric oxide film is repaired, hydrogen gas is generated due to the oxidation reaction, increasing the pressure inside the electrolytic capacitor, causing damage to the sealing part of the electrolytic capacitor, swelling of the explosion-proof valve, and shortening the life of the electrolytic capacitor. This could lead to shrinkage and loss of reliability. [Problems to be Solved by the Invention] Therefore, electrolytic capacitors that are resistant to this cleaning agent have been considered. For example, there is a method of coating the outer surface of the elastic sealing body with resin to prevent cleaning agents from entering the interior. However, this method has drawbacks such as poor reliability because it is difficult to uniformly apply the resin, and poor productivity because it takes a long time to cure the resin. Furthermore, in order to increase the corrosion resistance of the electrolytic capacitor element itself, corrosion inhibitors are also added to the electrolyte. Examples of such products include those in which a reaction product of alkanolamine and dibasic organic carboxylic acid or boric acid is added to an ethylene glycol-adipic acid electrolyte, as disclosed in JP-A-57-58311; Some of these have phosphoric acid or phosphate added to them. In addition, picric acid, which is used to reduce loss in electrolytic capacitors,
- It is known that additives such as nitrobenzoic acid are also effective in inhibiting corrosion, but these compounds affect the effects of addition on other properties of the electrolyte, especially determining the working voltage of electrolytic capacitors. It has the disadvantage of lowering the spark voltage, making it unsuitable for obtaining high-voltage electrolytic capacitors. Also, there are cases in which p-nitrophenol is added, as in JP-A-54-93443 and JP-A-57-54312, whose main purpose is to absorb hydrogen gas generated by reactions inside the capacitor. , the effect of inhibiting corrosion is recognized. However, p-nitrophenol has an extremely high yellow coloring property, and it has the disadvantage that when manufacturing electrolytic capacitors, workers, manufacturing equipment, and the exterior of the electrolytic capacitor itself are colored, making it extremely difficult to manufacture electrolytic capacitors.
Furthermore, the hydrogen gas absorption characteristics were insufficient for electrolytic capacitors that require advanced characteristics. This invention improves the conventional drawbacks, and prevents corrosion of electrolytic capacitors due to halogen-based substrate cleaning agents, prevents a drop in spark voltage, and suppresses the generation of hydrogen gas inside the electrolytic capacitor.
The aim is to obtain highly reliable and long-life electrolytic capacitors. [Means for Solving the Problems] In order to achieve the above object, the present invention adds m-
It has been found that the addition of nitrophenol is extremely effective. That is, this invention is characterized in that m-nitrophenol is added to a main electrolytic solution prepared by dissolving an inorganic acid, an organic acid, or their salts in a solvent mainly composed of ethylene glycol. The electrolytic solution of the present invention is selected from meta-position isomers of nitrophenol. m-Nitrophenol is a pale yellow crystalline powder that is not needed in water, but is easily soluble in alcohols and glycols, so the main electrolyte to be added is
It is preferable to use ethylene glycol as the main solvent. Further, the preferable range of the amount added is 0.1 wt% to 10 wt% with respect to the main electrolyte. [Function] By being added to the electrolytic solution, m-nitrophenol prevents corrosion of the electrode portion due to chlorine ions of the halogen-based cleaning agent entering from the outside. Further, the drop in spark voltage due to addition is small, and furthermore, the generation of hydrogen gas due to oxidation reaction is suppressed. [Example] The present invention will be described in detail below based on Examples. First, as a basic electrolyte, an ethylene glycol-adipic acid electrolyte is prepared by dissolving adipic acid or its ammonium salt in ethylene glycol as a solvent, and an ethylene glycol-boric acid electrolyte is prepared by dissolving boric acid or its ammonium salt in ethylene glycol. Prepare three types of electrolytes: ethylene glycol-benzoic acid electrolytes in which benzoic acid or its ammonium salt is dissolved, and use only these electrolytes and m
-Characteristics were compared with those to which nitrophenol was added. Table 1 shows the amount of m-nitrophenol added to the electrolytic solution of each system, and the one without additive was taken as the conventional example.

[Table] High-voltage electrolytic capacitors were created using these electrolytes, and the created electrolytic capacitors were washed in trichlorotrifluorethane vapor for 5 minutes and then subjected to a high-temperature load life test to determine the differences in their characteristics. Examined. The ratings and test conditions for the electrolytic capacitors created at this time were as follows: Those using an ethylene glycol-adipic acid electrolyte had a rating of 160WV.
Life test is 4.7μF and 1000 hours load test at 85℃. For those using ethylene glycol-boric acid electrolyte, the load test is rated at 350WV-1μF at 85℃ for 1000 hours. The one using ethylene glycol-benzoic acid electrolyte is rated at 250WV-22μF at 130℃,
A 1,000-hour load test was carried out on 25 samples each, and after the test was completed, each was disassembled and the presence or absence of corrosion was examined. The results are shown in Table 2.

【table】

[Table] As is clear from the above results, the electrolytic capacitor using the electrolyte of the present invention shows almost no corrosion in the high-temperature load life characteristics after cleaning with halogenated hydrocarbon, and has excellent corrosion resistance. It can be seen that it exhibits excellent characteristics. In this invention, as is clear from the results in Table 2, if the amount of m-nitrophenol added is extremely small, sufficient corrosion resistance cannot be obtained. From this result, in any type of electrolyte, the addition amount can be adjusted to almost the same as the basic electrolyte.
It can be seen that addition of 0.1 wt% or more is preferable. Regarding the upper limit of the amount added, the corrosion resistance tends to increase as the amount added increases, but when the amount added exceeds a certain amount, the spark voltage decreases, making it impossible to use it as a high-pressure electrolyte. Table 3 shows the relationship between the amount of m-nitrophenol added and the spark voltage in the ethylene glycol-benzoic acid electrolyte.As can be seen from this table, when the amount added exceeds 10wt%, the spark voltage decreases. Since the content starts to decrease, it is preferable to add 10 wt% or less. In addition, as the amount of addition increases, the resistivity value also tends to increase, which tends to affect electrical properties such as loss and equivalent series resistance. I don't like it from any point of view. Regarding the upper limit of this addition amount, almost the same results were obtained for other types of electrolytes.

[Table] Next, the effect of suppressing hydrogen gas generation was investigated. In the test, electrolytes of the three systems shown in Table 1 were added with m-nitrophenol in a medium amount of the present invention examples (present invention examples 12, 22, and 32).
As conventional examples for comparison, conventional examples 11, 21, and 21, in which the same amount of p-nitrophenol was added, were used.
31, an electrolytic capacitor was created using these electrolytes, and a load test was conducted to determine the bulge state of the sealing body itself or the explosion-proof valve installed in the sealing body, which is affected by the increase in internal pressure due to the generation of hydrogen gas. I looked into it. The results are shown in Table 4. Note that the ratings and test conditions of the produced electrolytic capacitors are the same as those in Table 2 except for the test time.

【table】

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent electrolytic capacitors from being corroded by halogen ions such as chlorine, and also to suppress the generation of hydrogen gas inside, making them highly reliable and capable of being used for long periods of time over a wide temperature range. You can get an electrolytic capacitor. In addition, m-nitrophenol has a lower coloring property than other isomers of nitrophenol, so it does not stain the hands and clothing of workers, manufacturing equipment, or even the product itself, making it easier to work with. .

Claims (1)

[Scope of Claims] 1. An electrolytic capacitor driving device characterized in that m-nitrophenol is added to a main electrolytic solution prepared by dissolving an inorganic acid, an organic acid, or their salts in a solvent mainly composed of ethylene glycol. Electrolyte. 2. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the amount of m-nitrophenol added is in the range of 0.1 wt% to 10 wt% with respect to the main electrolytic solution.