DE1564666B2 - METHOD FOR MANUFACTURING AN ALUMINUM ELECTROLYTE CONDENSER - Google Patents

Description

The invention relates to the manufacture of an aluminum electrolytic capacitor.

In the case of aluminum electrolytic capacitors, if the storage is de-energized, the Electrolyte hydrates the dielectrically effective aluminum oxide layer, especially at elevated temperatures. This reduces the blocking effect of the oxide layer. This effect can go so far cause the capacitor to fail when a voltage is applied again due to excessive residual current. Capacitors with “wet” electrolytes as a cathodic coating are particularly exposed to this risk. In the case of capacitors whose cathodic coating is formed by a manganese dioxide layer, this adverse effect occurs during the formation of the manganese dioxide layer. The formed Aluminum anode immersed in an aqueous solution of a manganese salt. From the formed on the Salt solution adhering to aluminum anode is formed by pyrolysis of manganese dioxide.

Since the pyrolysis takes place at an elevated temperature, this can be done by forming during this work step produced alumina can be hydrated. This results in an increase in the residual current.

It is already known to reduce an increase in residual current from such capacitors by that the surface is formed in several tension levels, each tension level being carried out in two baths and between these two baths the foils are dried by means of a heater. This method is intended to prevent the formed layer from being partially in each individual forming stage colloidal goes into solution, but does not prevent hydration on storage after forming.

The aim of the present invention is to provide a dielectric with a corresponding forming treatment to produce effective alumina that increases its resistance to hydration is.

According to the invention this is achieved in that after reaching the final forming voltage

ίο voltage-free intermediate treatment of the aluminum anode is carried out at 90 ⁰ C for 4 to 9 minutes in 0.5 to 5% citric acid solution.

The method according to the invention can be carried out according to the following example, but is not limited to this example: Roughened and boiled aluminum foil was preformed in stages in the usual preforming electrolytes (citric acid and boric acid-borax solutions). The final forming voltage at the four last forming stages was 440 V. After passing through the first two 440 V forming stages, part of the film was treated with 1% citric acid at 90 ° C. for 4 minutes without tension. The foil then passed through the remaining two forming stages at 440 V. 350/385 V electrolytic capacitors were built from the foils. After an initial measurement, the electrolyte capacitors were stored without tension at 65 ° C. The table shows the capacity of the electrolytic capacitors, the number of pieces in the initial measurement and the increase in the residual current (measured 5 minutes after applying 385 V) as well as the percentage of failures due to increased residual current after 1000 hours of storage at 65 ^° C.

capacitor
group

Intermediate treatment
lung

Yes
no

capacity

112
96

Starting quantity

37 24

More specific
Residual current

(ηΑΙμΈ V)
Oh 1000h

6th
6th

31
48

Failures (7o)

The intermediate treatment with hot citric acid brings a gain in capacity, but in the generally has a lesser extent. The difference in capacity in the example is for the most part due to a change in specific capacity over the length of the film.

Claims (1)

Claim: Process for the production of aluminum electrolytic capacitors, in which by forming a dielectrically effective oxide layer is generated on the anode surface and during a tension-free intermediate treatment is inserted after forming, characterized in that, that after reaching the final forming tension, the tension-free intermediate treatment the aluminum anode is made at 90 ° C for 4 to 9 minutes in 0.5 to 5% citric acid solution.