DE2401146A1 - Activation of anode foils for electrolytic capacitors - using two-stage process for providing anodic oxide film in activating bath - Google Patents

Abstract

The anode foils for electrolytic capacitors are activated in two stages, during which they are provided with an anodised oxide film. The first stage takes place in known activating baths with conventional activating electrolytes, while the second stage provides the final activation of the anode foil in an operating electrolyte which will eventually be used in the capacitor proper. Pref. the anode foils are made of Al and the operating electrolyte for the second stage and the capacitor operation consists of a glycol-borate-phosphate soln.

Description

Process for forming anode foils for electrolytic capacitors.

The invention relates to a method for forming anode foils for electrolytic capacitors, in which the anode foils are in forming stages iiu.t be provided with an anodically generated oxide layer. Such a process is obtained e.g. from DT-OS 2 141 004.

There a two-stage formation process is described in which the anode foils are treated in electrolytes with the same anions in both stages but different current densities are used in the two forming stages will.

From DT-PS 862 197 is a method for producing an aluminum oxide layer known on anode foils for electrolytic capacitors, the foil in several Steps is formed within a single forming bath.

Also from CH-PS 303 433 is a process for the formation of Anode foils for electrolytic capacitors are known, the foil running through three baths with the same electrolyte.

For the production of electrolytic capacitors you need one - optionally roughened - anode foil, which is used as a dielectric Oxide layer is provided. This oxide layer is applied to a foil during the Formrnierui Applied from a valve material such as aluminum, tantalum, niobium or zirconium.

The anodes are made from this foil, which is provided with an oxide layer for the electrolytic capacitors obtained by cutting to the desired width. These anode foils are used together with a cathode foil and spacers, which usually consist of paper layers, wound up and with the operating electrolyte soaked. The final step is reshaping, with the first step the defects in the oxide layer that occurred during processing are eliminated and, secondly, an improvement in the formed oxide layer is also achieved.

During the reforming process, the oxide layer is on the anode foil exposed to a strong interaction with the operating electrolyte. This interaction can because of the high demands on the roughness factors of the anode foil and the compact Build-up of the capacitors to high failure rates or loss of quality as a result local overheating in the winding, drying out of the operating electrolyte in the winding or change in the electrolyte composition in the coil due to toe effects.

The object of the present invention is to provide a forming process for Specify anode foils for the production of electrolytic capacitors, which the the above-mentioned deficiencies are eliminated, through which the interactions between the oxide layer serving as the dielectric and the operating electrolyte during the reforming process can be reduced compared to the known methods and which in particular leads to a better residual current behavior of the finished capacitor leads.

This task is carried out in a method of the type specified at the beginning solved in that the first forming stage in a known manner in forming baths with conventional forming electrolyte takes place and then represents the formation the anode foil in the second forming stage in the operating electrolyte used later is carried out The inventive method is a A number of advantages obtained due to the fact that the interaction between the dielectric layer and the operating electrolyte instead of in the finished product Electrolytic capacitor when reforming already got forming of the testicle foil be carried out. It can in contrast to the heat developed during this process finished winding can be easily removed in the forming bath.

You therefore have a precisely defined and uniform temperature the anode foil during the treatment time in the operating electrolyte. It can also because of the easier energy dissipation in a forming bath stage with stronger voltage and temperature loads of the anode foils are worked in the forming bath, a.

that there is a risk that these higher loads will lead to inhomogeneities lead in the dielectric layer. The size of the charge turnover in the case of the invention The process is not subject to any critical winding or cup conditions.

During the forming and post-forming process, the oxide layer additional anions incorporated. The interaction takes place through the method according to the invention between the operating electrolyte and the oxide layer not during the reforming process instead, so that selective electrolyte consumption in the forming bath is anticipated and do not lead to the detriment of the operating electrolyte that is scarce in the coil. Furthermore, the incorporation of anions into the oxide layer can also lead to changes in the composition of the operating electrolyte, as once the component is consumed more quickly with the lowest concentration and on the other hand anyway there is an uneven installation of the various components in the oxide layer.

It is already known to use anode foils in the operating electrolyte that will be used later to be fully formed, but j is to take into account that at Forming electrolytes have different requirements than those used later Operating electrolytes.

The inventive method is based on the fact that dielectric layers Produce with good electrical properties only in special forming electrolytes permit. According to the invention, the forming in the last forming stage occurs later operating electrolytes used, resulting in the advantages listed above. Overall, it can be said that by the inventive method a large Simplification of the reforming process is achieved.

The inventive method is suitable for the production of Anode foils for electrolytic capacitors for all voltage and temperature ranges, So for both high-voltage and low-voltage electrolytic capacitors and also for electrolytic capacitors with extended temperature range.

The operating electrolyte can be an aqueous or low-water glycol borate phosphate solution or based on organic solvents, such as dimethylformamide or Dimethylazetamid be built up, these operating electrolytes # only for example may be mentioned without the process according to the invention being restricted thereto.

The forming bath temperature can be between 80 and 1000 C, however this temperature also depends on the electrolyte used, so that of In some cases, lower or higher temperatures can also be selected. Preferably however, the selected temperature is replaced by the maximum permissible operating temperature of the Electrolytic capacitor determined.

In addition to the advantages of the erfindungsgern.uellen already listed above By simplifying the post-forming process, the residual current behavior is also reduced the electrolytic capacitors improved, the anode foils of which are treated according to the invention were, and there is also a stabilization of the electrical values at thermal Determine the load on the electrical capacitors compared to the known capacitors.

The advantages of the process according to the invention are detailed shown in the following embodiment.

Electrolytic capacitors were produced, their anode foils consisted of aluminum, in a known manner in a forming process in one conventional electrolytes, e.g. in 0.2% aqueous citric acid solution 90 ° C an oxide layer had been applied. The forming tension was approx. 400 V. A glycol-borate-phosphate electrolyte with an additive is used as the operating electrolyte of ammonia (composition approx. 1 mol H3B03, approx.

2 mol of glycol, approx. 0.2 mol of NH3 and approx. 0.01 mol of H3P03 per kg of electrolyte).

The electrolytic capacitors subjected to the method according to the invention were also in 0.2% aqueous citric acid solution in the first forming stage formed at 900 C and then in the second forming stage in the aforementioned Operating electrolyte formed at 850 C.

The following table shows the values for the capacity C, for the Loss factor tg #, for the impedance at 10 kHz Z as well as for the residual current ID (1 mine after applying the nominal voltage UN) and for the residual current 1R (5 mine after Applying the nominal voltage 5 UN).

The table shows the values immediately after completion of the electrolytic capacitors (the first number of the relevant value) and after storage without tension for 80 hours at 60 ° C (second numerical value), during which the capacitors cooled three times to room temperature within these 80 hours were (every 20 hours). The upper column shows the numerical values for the electrolytic capacitors whose anode foils were formed by the method according to the invention, while the second column shows the numerical values of the electrolytic capacitors formed according to the known method. UN / VC / µF tg # /% Z / # IR1 / µA IR / 5µA 360 490 468 2.0 2.0 0.050 0.056 728 509 216 230 360 495 493 1.9 2.0 0.052 0.058 1118 590 384 321 It can be seen from the table that the forming process according to the invention leads to electrolytic capacitors whose residual current behavior is significantly better than that of the electrolytic capacitors which have been treated according to the known forming processes.

12 claims

Claims (12)

Claims 1. A method for forming anode foils for Electrolytic capacitors, in which the anode foils in two forming stages with an anodically generated oxide layer can be provided z e i c h n e t that the first forming stage in a known manner in forming baths with conventional forming electrolytes and then the forming of the The anode foil in the second forming stage is carried out in the operating electrolyte used later will. 4, method according to claim 1, g e k e n n n z e i c h n e t by the Use of anode foils made of aluminum. 3. The method according to claim 1 or 2, g e k e n n z e i c h n e t through the use of an aqueous or low-water GlyRol-Borat-P1lospllat solution existing operating electrolytes in the second forming stage. 4. The method according to any one of claims 1 to 3, g e k e n n -z e i c h n e t through the use of a solvent-based operating electrolyte in the second forming stage, in particular based on dimethylformamide or Dimethylazetamide. 5. The method according to any one of claims 1 to 4, g e-k e n n -z e i c h n e t through the use of an operating electrolyte in the second forming stage, to which phosphates and / or polyphosphates are added. G. The method according to any one of claims 1 to 5, d a d u r c h g e k to note that the forming baths of the first and second stages are the same Have bath temperatures. 7. The method according to any one of claims 1 to 5, d a d u r c h g e k It should be noted that the forming baths of the first and second stages are different Have temperatures. 8. The method according to any one of claims 1 to 7, d a d u r c h g e k It is noted that the bath temperatures are based on the maximum permissible operating temperature of the electrolytic capacitors. 9. The method according to any one of claims 1 to 8, d a d u r c h g e k E n n z e 1 c h n e t that the bath temperatures are between 80 and 1000 C. 10. The method according to any one of claims 1 to 9, d a d u r c h g e it is not indicated that the voltage applied in the second forming stage is equal to or greater than the nominal voltage of the capacitors to be manufactured. 11. The method according to any one of claims 1 to 9, d a d u r c h g e It is not shown that the voltage in the second forming stage is selected to be lower is called the voltage in the first forming stage. 12. The method according to any one of claims 1 to 11, d a d u r c h g e it is not indicated that the formation in the first stage takes place in several steps he follows.