JPH0581045B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a method for manufacturing a long-life aluminum electrolytic capacitor intended for use in power supplies for electronic exchanges, etc. "Conventional technology" Conventionally, the lifespan of aluminum electrolytic capacitors used in power supplies for electronic exchanges, etc. is 7 to 10 years.
Due to its short lifespan compared to the 20+ year lifespan of the equipment, periodic replacement was required. Aluminum electrolytic capacitors are made by anodizing aluminum etched foil to form a dielectric oxide film (Al ₂ O ₃ ) on its surface, and then bonding this anodized aluminum foil and the cathode aluminum etching foil through electrolytic paper. Wind it up to make a capacitor element. Furthermore, this element is vacuum impregnated with an electrolyte solution, a terminal plate is attached, and then the element is sealed in a case and subjected to an aging treatment. For large capacitors with a capacitance of several thousand μF or more and a rated voltage of 50V or more, which are used in power supplies for electronic exchanges, etc., after impregnating the capacitor element with electrolyte, the excess is generally removed in consideration of workability. The electrolyte is squeezed out to prevent it from leaking. Aluminum electrolytic capacitors made in this way are used under various conditions after being shipped, but a small amount of leakage current (1mA or less) flows during use, so if used for a long time, This leakage current gradually electrolyzes the electrolyte, resulting in gas generation and gradual depletion of the electrolyte. In addition, the gas and evaporated components of the electrolyte generated by leakage current diffuse through the sealing material itself such as rubber packing and the gaps between the sealing parts, and escape out of the capacitor case in small amounts over a long period of time. The liquid gradually decreases and changes in quality.
Therefore, as for the electrical characteristics, the capacitance gradually decreases and the tan δ increases as time passes. As the electrolyte continues to deplete, the capacitance value rapidly decreases after a certain point, and the tan δ value also rapidly increases, reaching the end of the capacitor's lifespan. This condition is accelerated when the ambient temperature in which the capacitor is used is high or when the ripple current flowing through the capacitor is large. Generally, the lifespan of aluminum electrolytic capacitors used in electronic switching equipment is said to be 7 to 10 years, although it varies depending on the conditions of use. Conventionally, the following methods have been known to extend the life of aluminum electrolytic capacitors. (1) Use low-magnification foil for the anode to reduce equivalent series resistance (ESR) and suppress temperature rise due to ripple current. (2) Use a solvent with low vapor pressure for the electrolyte, or suppress evaporation of the gelled electrolyte. (3) Improve the airtight structure of the case. (For example, double cases, etc.) However, in (1) of the above upper rows, using low-magnification foil reduces the capacitance per unit area, so extra electrode foil (anode, cathode, etc.) is needed to ensure the specified capacitance. ), which has the disadvantage of inevitably increasing the case size. Also (3)
However, it also has the disadvantage that the case size becomes large. Furthermore, although the evaporation of the electrolyte is suppressed in the method (2), the equivalent series resistance (ESR) of the electrolyte increases, leading to an increase in tanδ and a decrease in the allowable ripple current, which is not necessary for practical use. The drawback is that it is not possible to extend the lifespan without deteriorating the electrical characteristics. An object of the present invention is to provide a manufacturing method that solves the above-mentioned drawbacks of the prior art and allows an aluminum electrolytic capacitor to be obtained with a longer lifespan than conventional capacitors without causing deterioration of electrical characteristics. "Means for Solving the Problems" In order to extend the life of an aluminum electrolytic capacitor, the present invention impregnates the capacitor element with an electrolytic solution in the usual manner, that is, vacuum impregnates it, and then places it in a case. Before sealing the case, the amount of electrolyte is increased by further injecting an electrolyte of about 10% or more of the weight of the impregnated electrolyte. Furthermore, as aluminum etched foil for anodes, it has a higher surface area than high-magnification aluminum etched foil, that is, non-etched aluminum foil.
Leakage current is reduced and gas generation is suppressed by using a foil that is approximately 100 times larger and anodized at a voltage 1.3 to 2 times the rated voltage to create a thicker anodic oxide film. Also used as etching foil for cathode, 99.9%
High purity aluminum etching foil
A thin oxide film formed by anodization at a formation voltage of about 5V is used to reduce leakage current and the amount of gas generated. "Example" Next, an example of the present invention will be shown. Test 1 A commercially available aluminum etched foil for anodes was applied to a voltage 1.7 times the rated voltage (if the rated voltage is 63V, approx.
105V) to form an oxide film.Similarly, an oxide film is formed on the etched foil for the cathode at about 5V, and these are wound using manila paper as electrolytic paper to make a capacitor element. Next, this element is impregnated with an electrolytic solution whose main components are ethylene glycol and ammonium adipate, a terminal board is attached, and the device is housed in a case. After that, an electrolytic solution equivalent to about 20% of the weight of the impregnated electrolytic solution is injected. Increase volume and seal. The rating manufactured in this way is 63V,
Figure 1 shows the capacitance change rate (average value of five capacitors) over time when a 17,000-hour test was conducted with a 2,200 μF capacitor at 85°C and a 63V DC voltage applied. ) shows the aging characteristics of an aluminum electrolytic capacitor whose life has been extended by the present invention, or which is manufactured almost in the same way as the prior art, but before sealing the capacitor element in the case, approximately 20% of the weight of the impregnated electrolyte is % shows the aging characteristics of an aluminum electrolytic capacitor according to the present invention in which the amount of electrolyte was increased by injecting an amount of electrolytic solution corresponding to 100%. As shown in the figure, the capacitance change rate after 17,000 hours is as small as -1% or less in the case of the present invention, and it is extremely stable. In contrast, in the case of the conventional product, the capacitance gradually decreases until 10,000 hours, then rapidly decreases, and shows a -14% change rate after 17,000 hours. In addition, the electrolyte was added to the conventional product.
In this invention, the amount was increased by injecting 20% by weight.
The capacitance change rate after 17000 hours is -8%,
It can be seen that the aging characteristics are considerably improved compared to the conventional product without increasing the amount of electrolyte. In this case, in addition to the effect of increasing the amount of electrolyte, the oxide film on the anode foil was thickened, the oxide film was also formed on the cathode foil, and the electrolytic paper had a low density and good ability to retain the electrolyte. By using Manila paper, it was possible to significantly reduce the rate of change in capacitance over time and extend the lifespan. Test 2 After making capacitor elements in the usual way and impregnating them with electrolyte, the electrolyte was increased by 10%, 20% and 30% by weight before being sealed in the case, and each aluminum electrolytic capacitor rated at 63V was used. Table 1 shows the average value of the capacitance change rate when 5 units were manufactured and an unloaded test was conducted at 85℃ for 3000 hours with the explosion-proof valve removed to accelerate the drying of the electrolyte. show.

[Table] As is clear from the results, the capacitance change rate decreases as the amount of electrolyte increases, confirming that increasing the amount of electrolyte effectively works to improve life characteristics. This increase is preferably 10 to 20% by weight. Increasing the weight by 30% will extend the lifespan, but will also require a larger case. Test 3 Anode foil and cathode foil were made using the method described in Test 1, and each was wound using three types of electrolytic paper: Manila paper, Kraft paper, and high-density paper plus mixed paper (Manila, Kraft). After making an element and impregnating it with electrolyte using the usual method, it is placed in an aluminum case and left unloaded for 400 hours at 85°C with the terminal board removed. The average values (average values of each 5 samples) are shown in Table 2. As is clear from this result, when Manila paper is used as electrolytic paper, the rate of change in capacitance is the smallest, and therefore compared to other electrolytic papers, Manila paper has better electrolyte retention and improves life characteristics. I was able to confirm that it was effective.

[Table] Test 4 Using commercially available aluminum etched foil, the anode foil was anodized at 1.3 times and 1.7 times the rated voltage to form an oxide film, and 5 capacitors each with a 63V rating were manufactured using the usual method. Table 3 shows the results of testing for 7,000 hours at 85°C and applying a DC voltage of 63V. All values are the average of five values.

[Table] As is clear from the results, it was confirmed that the higher the anode foil formation voltage was compared to the rated voltage, the smaller the capacitance change rate and the better the life characteristics.
However, if the anodization voltage is too high, the oxide film becomes too thick and the capacitance decreases, so it is preferably about 1.3 to 2 times the rated voltage. Test 5 Using commercially available aluminum etched foil, the anode foil was anodized at twice the rated voltage to form an oxide film, and the cathode foil was anodized at about 5V and without. Table 4 shows the rate of change in capacitance and the amount of decrease in capacitor weight when 10 tubular electrolytic capacitors were manufactured and then subjected to a DC load test for 5000 hours at 85°C.

[Table] As is clear from this result, when the cathode foil is anodized, both the capacitance change rate and the amount of weight loss are smaller. We were able to confirm that it is effective to chemically form a thin oxide film. "Effects of the Invention" According to this invention, the life of the capacitor can be extended by increasing the amount of electrolyte, and by using the capacitor obtained by the method of this invention, the number of periodic replacements can be reduced, or the number of periodic replacements can be reduced. There will be no need. Moreover, the manufacturing method of this invention has the advantage that conventional manufacturing equipment can be used as is, with only an additional step for increasing the amount of electrolyte, so the manufacturing cost remains almost the same, and therefore it is industrially and economically viable. is also extremely advantageous. In this invention, aging deterioration is minimized by thickening the anodic oxide film of the anode etching foil.
As the anodic oxide film becomes thicker, the capacitance decreases. However, this invention uses aluminum etched foil with a high magnification, that is, the surface area is increased by about 100 times by etching the surface to form irregularities, which compensates for the decrease in capacitance and increases the external dimensions of the capacitor. There's no need. Also, according to Test 1, even after carrying out the test for 17,000 hours at a temperature of 85°C and applying a DC rated voltage,
The capacitance change rate was -1% or less, and no external abnormalities such as electrolyte leakage or explosion-proof valve operation were observed. From this result, compared to conventional aluminum electrolytic capacitors, the lifespan can be more than doubled without increasing the case size.

[Brief explanation of the drawing]

Figure 1 shows the results of a DC rated voltage application test at 85°C conducted on aluminum electrolytic capacitors manufactured according to the present invention and aluminum electrolytic capacitors manufactured using conventional technology, showing the rate of capacitance change over time. FIG. 3 is a diagram showing characteristics. , : Aluminum electrolytic capacitor manufactured by the method of the present invention, : Aluminum electrolytic capacitor according to the prior art.

Claims (1)

[Scope of Claims] 1. High-magnification aluminum etching foil for anode anodized at an anodizing voltage of 1.3 to 2 times the rated voltage, and 99.9 anodized foil anodized at an anodizing voltage of 5 V to form a thin oxide film on the surface. A capacitor element is made by winding aluminum etched foil for a cathode with a purity of at least 50% through electrolytic paper, impregnating the capacitor element with an electrolyte, and placing the capacitor element impregnated with the electrolyte in a case. of the weight of the above impregnated electrolyte before sealing the case.
A method for manufacturing a long-life aluminum electrolytic capacitor, characterized by injecting 10% or more electrolyte into the case.