JP4198584B2 - Aluminum foil for electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electrolytic capacitor aluminum foil used for an electrode of an electrolytic capacitor and a method of manufacturing the same.

The aluminum foil used for the electrode of the electrolytic capacitor has a function as a capacitor electrode by forming an oxide film on the surface. By the way, the surface of the aluminum foil for electrolytic capacitors is electrically etched (for example, direct current etching) prior to the formation of the oxide film in order to increase the capacitance per unit area when used as an electrode. A treatment for roughening and increasing the surface area is generally performed. In this roughening, since the surface area is increased by forming a large number of minute pits on the surface of the aluminum foil, various ideas have been made to improve the roughening rate by dispersing pits with high density and uniformity. Yes. As one of the techniques, it has been proposed to promote the formation of pits by adding a small amount of various elements as components of the aluminum foil (for example, Patent Document 1).
JP-A-5-287465

  However, many of the components contained in a trace amount in the aluminum foil have an effect of causing ineffective dissolution and inhibit roughening. For this reason, there is a problem that even if a component effective for pit formation is added, the pit formation effect is hindered by ineffective dissolution, and only an insufficient result in roughening can be obtained.

  The present invention has been made against the background of the above circumstances, and for electrolytic capacitors capable of obtaining a high capacitance by forming pits uniformly and with high density and pit formation enough in direct current etching and the like. An object is to provide an aluminum foil and a method for producing the same.

  That is, the aluminum foil for electrolytic capacitors of the present invention has a mass ratio of Fe: 5 to 100 ppm, Si: 5 to 100 ppm, Cu: 1 to 100 ppm, Pb: 0.1 to 5 ppm, rare earth element: 0.1 to 10 ppm, Sn: 0.5 to 5 ppm is contained, and the balance is 99.9% or more of Al and inevitable impurities.

Moreover, in addition to the said component, Zn: 1-20ppm can be contained by mass ratio further.
Moreover, in addition to the said component, Zr: 1-50ppm can be contained by mass ratio further.
Furthermore, in each of the above components, the total amount of Mn, Mg, Cr, Ti, B, V, and Ga in the inevitable impurities can be made 10 ppm or less.

  Moreover, invention of the manufacturing method of the aluminum foil for electrolytic capacitors of this invention is 1-12 at 200-400 degreeC as final annealing to the aluminum foil which has one of said compositions and was finally cold-rolled. It is characterized by holding for 4 to 12 hours at 500 to 600 ° C. after holding for a period of time.

Below, the reason which prescribed | regulated each component and manufacturing condition in this invention is demonstrated.
Fe, Si: 5 to 100 ppm each
Si and Fe are dispersed as an Al—Fe—Si intermetallic compound on the alloy surface to serve as pit starting points and increase the pit density. However, if the amount is less than 5 ppm, it is insufficient to obtain the above-described effect. On the other hand, if it exceeds 100 ppm, the pit density becomes excessive and the pits coalesce and the surface expansion rate does not increase. For this reason, the contents of Si and Fe are each set to 5 to 100 ppm. For the same reason, it is desirable that the lower limit of the Si and Fe contents is 10 ppm, the upper limit is 50 ppm for Si, and 30 ppm for Fe.

Cu: 1 to 100 ppm
Cu is contained in order to promote the formation of the anode coating and the formation of the cathode coating thereon. However, if the amount is too small, the anode coating and the cathode coating are not sufficiently formed, and the ineffective dissolution that hardly contributes to the surface expansion proceeds. On the other hand, if the amount is excessive, the anode coating and the cathode coating become too thick and it becomes difficult to form coating defects, and the formation of pits from the defective portion is hindered, so the upper limit is made 100 ppm. For the same reason, it is desirable to set the lower limit to 5 ppm and the upper limit to 60 ppm.

Pb: 0.1-5 ppm
Pb has an action of promoting pit formation, and is contained in an amount of 0.1 ppm or more in order to sufficiently obtain this action. However, if the content exceeds 5 ppm, an effect of ineffective dissolution and inhibition of roughening is observed, so the Pb content is limited to the above. For the same reason as described above, it is desirable to set the lower limit of Pb to 0.3 ppm and the upper limit to 2 ppm.

Rare earth elements: 0.1 to 10 ppm
Sn: 0.5-5 ppm
The coexistence of rare earth elements and Sn has an effect of uniformly dispersing pits at high density, and the effect is particularly remarkable in direct current etching. In order to obtain this effect sufficiently, it is necessary to contain 0.1 ppm of rare earth elements and 0.5 ppm of Sn. If any of these elements is lacking, the above effects cannot be obtained. On the other hand, since excessive dissolution of the surface layer occurs when these elements are excessively contained, the upper limit is 10 ppm for rare earth elements and 5 ppm for Sn. For the same reason as described above, the lower limit of the rare earth element is preferably 0.5 ppm and the upper limit is 3 ppm, and the lower limit of Sn is preferably 1 ppm and the upper limit is 3 ppm.

Al: Purity of 99.9% or more The purity of the aluminum foil needs to be 99.9% or more so that pits can be effectively formed during etching and good characteristics can be obtained as a capacitor when used as a capacitor electrode. is there. For the same reason, a purity of 99.98% or more is desirable.

Zn: 1 to 20 ppm
Zn has an effect of forming a film defect when the cathode film is formed, and can be contained as desired because it is an element that enhances the etching progress. However, if the content is less than 1 ppm, the above effect cannot be obtained sufficiently. If the content exceeds 20 ppm, the amount of defects is too much to promote ineffective dissolution, so the content in the case of inclusion is limited to 1 to 20 ppm. For the same reason, it is desirable to set the lower limit to 3 ppm and the upper limit to 15 ppm.

Zr: 1-50 ppm
Zr has an effect of enhancing the action due to the coexistence of the rare earth element and Sn, and is contained as desired. However, the content of 1 ppm or more is necessary to obtain the effect sufficiently. On the other hand, if Zr is contained in excess of 50 ppm, the recrystallization of aluminum is delayed, and a high cubic rate cannot be obtained. Therefore, the content when Zr is optionally contained is set to 1 to 50 ppm.

Total amount of Mn, Mg, Cr, Ti, B, V, and Ga: 10 ppm or less Mn, Mg, Cr, Ti, B, and V are elements that increase ineffective dissolution that inhibits roughening. The total amount of these elements is restricted to 10 ppm or less to prevent ineffective dissolution. Further, the total amount of Mn and the like is desirably 8 ppm or less for the same reason as described above.

Final annealing: 200-400 ° C x 1-12 hours
After the end of cold rolling at 500 to 600 ° C. for 4 to 12 hours, the aluminum foil is subjected to final annealing under the above-described conditions, so that Sn contained in the foil can be concentrated on the surface to enhance the effect of Sn.
In order to sufficiently condense Sn, it is necessary that the heating in the previous stage is 200 ° C. or higher and the holding time is 1 hour or longer. On the other hand, since the effect is saturated even if it exceeds 12 hours, the holding time is set to 12 hours or less. Further, if the heating temperature is higher than 400 ° C., the surface concentration of other elements proceeds and Sn cannot be sufficiently concentrated on the surface, so that the pretreatment conditions are 200 to 400 ° C. × 1 to 12 hours. Moreover, since the objective of the latter stage heating is to sufficiently develop cubic crystals, heating at 500 ° C. or higher is required. If the temperature exceeds 600 ° C., melting of aluminum starts and serious problems such as adhesion of the foil occur. Therefore, the upper limit is set to 600 ° C. Regarding the holding time, 4 hours or more are required for the growth of cubic crystals, and the effect is saturated even if held for more than 12 hours. In the above-mentioned two-stage heating, it is desirable that the temperature is continuously raised after the former stage heating and then the latter stage heating is performed. However, after the former stage heating, the latter stage heating can be performed through a cooling process.

  As described above, according to the aluminum foil for electrolytic capacitors of the present invention, by mass ratio, Fe: 5 to 100 ppm, Si: 5 to 100 ppm, Cu: 1 to 100 ppm, Pb: 0.1 to 5 ppm, rare earth element : 0.1 to 10 ppm, Sn: 0.5 to 5 ppm, with the balance being 99.9% or more of Al and inevitable impurities, especially by containing Sn and rare earth elements together, etching property And pit formation with high density and uniform dispersion becomes possible. As a result, a high roughening rate is obtained by etching, and a high capacitance is obtained when used as a capacitor. Further, if desired, the etching property can be further improved by containing Zn and Zr, and the amount of ineffective dissolution can be reduced by regulating the total amount of Mn, Mg, Cr, Ti, B, V, and Ga, and the rough surface. The conversion rate can be improved.

  Moreover, according to the aluminum foil for electrolytic capacitors of this invention, after hold | maintaining at 200-400 degreeC for 1 to 12 hours as final annealing to the aluminum foil which has the said composition and was finally cold-rolled, 500- Since it hold | maintains at 600 degreeC for 4 to 12 hours, the effect of the said aluminum foil can be made more remarkable with the concentration behavior of Sn.

Hereinafter, an embodiment of the present invention will be described.
A high-purity aluminum material prepared to be a component of the present invention with a purity of 99.9% or more can be obtained by a conventional method, and the production method is not particularly limited as the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used, or a high-purity aluminum material obtained by continuous casting can be used. Note that misch metal can be used when REM is contained. For example, a sheet material having a thickness of about several mm is formed by the hot rolling or continuous casting rolling. This sheet material is cold-rolled to obtain an aluminum alloy foil of about several tens of μm to 100 μm. It should be noted that degreasing may be appropriately added during the cold press or after the end of the cold press, and intermediate annealing may be appropriately added during the cold press.

  After the final cold rolling, as shown in FIG. 1, a final annealing heat treatment is preferably performed in which heating is performed at 200 to 400 ° C. for 1 to 12 hours in the former stage and 500 to 600 ° C. for 4 to 12 hours in the latter stage. In this example, after the former heating, the latter heating is performed by raising the temperature without cooling.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching process is performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. The present invention is not particularly limited with respect to specific conditions and the like of this etching treatment, and can be performed according to a conventional method, but DC etching is mainly applied.
In the etching process, pits are formed at a high density on the foil by setting the above components, and a high roughening rate is obtained and ineffective dissolution is suppressed. A capacitor having a high capacitance can be obtained by incorporating this foil as an electrode in an electrolytic capacitor by a conventional method.

  The present invention is preferably used as an anode of a medium-high voltage electrolytic capacitor. However, the present invention is not limited to this, and can be used for a capacitor having a lower formation voltage. It can also be used as a cathode material.

Examples of the present invention will be described below in comparison with comparative examples.
High-purity aluminum having the composition shown in Table 1 was melted, and a high-purity aluminum foil having a thickness of 110 μm was manufactured through hot rolling and cold rolling. These aluminum foils were subjected to final annealing under the conditions shown in Table 1. All high-purity aluminum foils were etched under the following conditions to roughen the aluminum foil.

(DC etching)
A direct current of 200 mA / cm ² was applied for 120 seconds in a 75 ° C HCl 1M, H ₂ SO ₄ 3M solution, and then a 50 mA / cm ² direct current was applied for 600 seconds in an 80 ° C HCl 2M solution.
In the etching, the weight of the aluminum foil before and after the etching was measured, and the decrease in weight was taken as the dissolution loss.
(Capacitance measurement)
The etching foil was cut into a size of 1 × 5 cm, formed at 300 ° C. with an 80 ° C. boric acid 80 g / l solution, and the capacity was measured in a 150 g / l adipic acid solution.

The dissolution weight loss and capacitance measured above were relative evaluated as percentages based on the dissolution weight loss and capacitance of Example 1. The evaluation results are shown in Table 2.
As can be seen from Table 2, all of the examples of the present invention exhibit good capacitance. In addition, among the examples, it has been clarified that those added with Zr have a higher capacitance than those not added. Furthermore, it became clear that what carried out the final annealing after cold rolling by 2 steps | paragraphs (Examples 13-15) improved an electrostatic capacitance compared with what performed the 1st step final annealing.

  On the other hand, in the comparative example, the electrostatic capacity was inferior to that of the example. Further, as seen in Comparative Examples 4 and 6, even when either REM (rare earth element) or Sn was contained, the effect of improving the capacitance was hardly seen. In addition, even when the Sn content was outside the specified range of the present invention (Comparative Example 5), good electrostatic capacity was not obtained.

It is a figure which shows the heat pattern of the last annealing in one Embodiment of this invention.

Claims (5)

In mass ratio, Fe: 5-100 ppm, Si: 5-100 ppm, Cu: 1-100 ppm, Pb: 0.1-5 ppm, rare earth element: 0.1-10 ppm, Sn: 0.5-5 ppm, An aluminum foil for an electrolytic capacitor, wherein the balance is 99.9% or more of Al and inevitable impurities. Furthermore, the aluminum foil for electrolytic capacitors of Claim 1 containing Zn: 1-20ppm by mass ratio. Furthermore, the aluminum foil for electrolytic capacitors of Claim 1 or 2 containing Zr: 1-50ppm by mass ratio. The aluminum foil for electrolytic capacitors according to any one of claims 1 to 3, wherein the total amount of Mn, Mg, Cr, Ti, B, V, and Ga in the inevitable impurities is 10 ppm or less. The aluminum foil having the composition according to any one of claims 1 to 4 and having been subjected to final cold rolling is held as a final annealing at 200 to 400 ° C for 1 to 12 hours, and then at 500 to 600 ° C for 4 hours. A method for producing an aluminum foil for electrolytic capacitors, characterized by holding for -12 hours.

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