DE2255309B2 - PROCESS FOR THE PRODUCTION OF ALUMINUM ELECTRODES FOR ELECTROLYTE CAPACITORS - Google Patents

Description

20th

The electrodes of an electrolytic capacitor are generally made of roughened, i.e. etched Aluminum bands. The roughening of the tape increases the surface area and thus increases the surface area Increase in capacity or, for a given capacity, a reduction in electrode dimensions is achieved

Pure aluminum is usually used as the starting material for the production of etched anode strips and pure aluminum or aluminum alloys containing manganese are used for the production of etched cathode strips. The ingots are heated in general to a hot forming temperature between 400 and 55O ⁰ C and mm to hot rolling stands to a plate thickness of 2-10 hot rolled, the slabs are rolled in several passes to final thickness to the strip cold and in this or any additional heat-treated state for etching used

The etched tapes produced in this way today often no longer meet the requirement for sufficient high roughness, which is the prerequisite for the construction of an electrolyte that is as small as possible in terms of volume capacitor is It was therefore necessary to find a method according to which even higher roughness than are possible according to the previously known methods.

For some years now, in addition to the aforementioned block (bar) casting, tape casting processes have also been experienced applied in practice. The material is taken directly from the melt in the form of a strip of 1–40 mm thick strip cast and then rolled further warm and then cold or directly cold to the final thickness.

For example, a method according to DT-AS 12 88 196 is known for producing aluminum electrode foils for electrolytic capacitors with an aluminum content of at least 99.45%, in which the foils are cold-formed by rolling and then etched without annealing treatment. This process is characterized in that the material used to produce the foils is heated ^{to at least 510 ° C. at any point in time before the deformation by cold rolling.}

The above-mentioned method is said to be the effective surface of the electrode foil material enlarged. In addition to the material annealing mentioned in this process, you can also use the subsequent etching favorable condition today through other measures, such as adding, of additives to the melt or by taking special measures during the melt flow However, measures are relatively complex.

The present invention is now based on the object of a method for the production of To create aluminum electrodes for electrolytic capacitors, with which the previously known Process inherent disadvantages for the production of such films, for example by a relatively costly material annealing are to be avoided.

The invention relates to a method of manufacture of aluminum electrodes for electrolytic capacitors, which are used in one chloride-containing electrolyte are electrolytically etched and which is characterized in that the for etching The aluminum strip used was cast directly as a strip from the melt phase and then cast to its final thickness is rolled.

The better etching behavior of the after the tape casting produced material results from the surface enlargement that occurs when moving from the liquid to the solid phase of the aluminum results in a volume shrinkage of approx. 7%. The relatively rapid solidification in the strip casting process favors the formation of Cavities, internal cavities, porous areas and leaks in the structure.

All of these properties are disadvantageous for the common use of aluminum. For the production of etched foils, however, this material has proven to be beneficial because the surface has an increased number of defects which act as additional etching attack points and because porous interiors in addition to Etching result in a contribution to the surface enlargement.

It has now been found that when comparing the cast strips and cast bars produced aluminum strips the former after the same etching treatment basically higher roughening demonstrate. This effect can be seen in both unalloyed and alloyed aluminum metal.

Examples

Depending on a Stranggußbarren of Al and from 99 AlMn 2 hours were annealed at 500 ⁰ C and then hot-rolled mm at a plate thickness of 6 and cold-rolled without heat treatment to 0.05 mm thick tapes. In comparison, one strip each from an Al-99 melt and from an AlMn melt was cast directly as a 7 mm thick strip in a strip casting plant and then rolled to the same final thickness without heat treatment. The strips were degreased and then etched in an aqueous solution of 20% NaCl at 90 ^° C., with a current density of 100 A / dm ² and a current of 3000 Cb / dm ² .

The capacity was determined according to DIN 41 330 at 0 and 10 volts in a saturated ammonium pentaborate solution with a bath resistance of 60 to 70 ohm cm at room temperature. Were determined also the mechanical characteristics of the tapes before etching. The results are in the following tables summarized:

Example 1 with Al 99

Example 2 with AlMn

Oi

0100

Capacity in

(kp / mm ² )

according to DIN 41 330

at

0 volts 10 volts

oe 0100 Capacity in HF / cm ² according to DIN 41 330 at (kp / mm ² ) (%) 0 volts 10 volts

Ingot casting 23.2 33 110 28 Ingot casting 32.5 2ß 240 60 Tape casting 24.0 3.4 150 40 Tape casting 323 3.8 350 100

The results show that the strength in the hard state is independent of the casting method In contrast, the result of the etching and the capacity measurement shows a significant increase in capacity Metal that was manufactured using the strip casting process.

Claims (2)

Patent claims: 1. Process for the production of aluminum electrodes for electrolytic capacitors, which in order to increase the surface area in a chloride-containing Electrolyte are electrolytically etched, characterized in that the for Etching used aluminum tape from the melting phase directly cast as a tape and then on ι ο Final thickness is rolled. 2. The method according to claim 1, characterized in that that the cast strip thickness is between 1 and 40 mm 15th