JP2009249668A - Aluminum foil for electrolytic capacitor, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance a roughening ratio when an aluminum foil for an electrolytic capacitor is etched. <P>SOLUTION: The aluminum foil having a composition, which contains, by mass, 10 to 30 ppm Si, 10 to 30 ppm Fe, 20 to 80 ppm Cu, 0.6 to 1.5% Pb, one or more selected from Zr, V, Mn, Zn, Ga and Na by 10 to 50 ppm in total and 0.1 to 10 ppm REM, and the balance ≥99.9% Al with inevitable impurities, and has the thickness of 100 to <125 μm, is subjected to final annealing at ≥500°C for ≥6 hr in an inert gas or a reducing gas or a mixed gas atmosphere thereof. Upon etching, pits are effectively and uniformly formed, and a roughening ratio can be improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

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.

Among the aluminum foils for electrolytic capacitors, the medium and high pressure foils are used by subjecting them to direct current electrolysis and opening countless holes in the surface layer to enlarge (roughen) the surface area. In order to uniformly generate etching pits, a foil having a cube orientation occupation ratio of 95% or more by performing final annealing after cold rolling is used. Furthermore, various proposals have been made regarding the additive elements in order to increase the generation efficiency of pits. (For example, see Patent Documents 1 and 2)
JP 2006-152394 A JP 2006-152402 A

However, the present situation is that the roughening rate is not sufficiently improved even if a trace amount of elements as in Patent Documents 1 and 2 is added.
In order to efficiently generate etching pits, the characteristics of the aluminum foil surface are important. In particular, control of the surface oxide film and control of the elements concentrated on the surface during annealing are important items.
The medium-high pressure foil uses a foil having a cubic orientation occupation ratio of 95% or more, and therefore requires high-temperature heat treatment at 500 ° C. or higher in the production process. It is known that the fine elements in the aluminum foil are concentrated on the surface by this heat treatment. However, the inventors of the present application have found that excellent etching properties can be obtained by appropriately blending elements according to the purpose from the knowledge that the degree of surface concentration differs depending on the element, and the present invention is completed. Has been reached.

  That is, the present invention was made against the background of the above circumstances, and an aluminum foil for electrolytic capacitors that can efficiently and uniformly generate etching pits by the compounding ratio of elements concentrated on the surface during annealing, and a method for manufacturing the same. The purpose is to provide.

  The aluminum foil for electrolytic capacitors of the present invention is one of Si 10-30 ppm, Fe 10-30 ppm, Cu 20-80 ppm, Pb 0.6-1.5 ppm, (Zr, V, Mn, Zn, Ga, Na) by mass ratio. Or it contains 10-50 ppm in total of 2 or more types, REM 0.1-10 ppm, the remainder has a composition consisting of inevitable impurities and 99.9% or more of Al, and has a thickness of 100 μm or more and less than 125 μm And

  The aluminum foil for electrolytic capacitors of the second aspect of the invention is characterized in that, in the aluminum foil for electrolytic capacitors of the first aspect of the invention, the oxide film thickness of the aluminum foil is 20 to 100 mm.

  The manufacturing method of the aluminum foil for electrolytic capacitors of 3rd this invention is mass ratio, Si10-30ppm, Fe10-30ppm, Cu20-80ppm, Pb0.6-1.5ppm, (Zr, V, Mn, Zn, Ga , Na) in a total of 10 to 50 ppm and REM 0.1 to 10 ppm, with the balance being inevitable impurities and 99.9% or more of Al, with a thickness of 100 μm or more and 125 μm Less than aluminum foil is subjected to final annealing at 500 ° C. or more for 6 hours or more in an atmosphere of an inert gas, a reducing gas or a mixed gas thereof.

  The method for producing an aluminum foil for electrolytic capacitors according to a fourth aspect of the present invention is the method for producing an aluminum foil for electrolytic capacitors according to the third aspect of the present invention, wherein the rate of temperature increase during the final annealing is 30 to 100 ° C./Hr. It is characterized by that.

  The manufacturing method of the aluminum foil for electrolytic capacitors of 5th this invention WHEREIN: In the manufacturing method of the aluminum foil for electrolytic capacitors of the said 3rd or 4th invention, in the middle of the cold rolling which manufactures the said aluminum foil, 200- It is characterized by performing intermediate annealing at 280 ° C. for 2 to 10 hours.

  Below, the composition and manufacturing conditions of the aluminum foil prescribed | regulated by this invention are demonstrated.

Aluminum purity: 99.9% or more When the purity of the aluminum foil is less than 99.9%, the cubic ratio is lowered, which is not desirable. Inevitable impurities include components specific to bullion. Even if three-layer metal or segregated metal is used, there is a problem if 99.9% or more is secured as aluminum purity after adjusting Si, Fe, Cu, Pb, Zr, V, Mn, Zn, Ga, and Na. There is no.

Si: 10-30 ppm
Fe: 10-30ppm
When Si and Fe are less than 10 ppm, the purification cost increases, which is undesirable industrially. On the other hand, when Si and Fe are more than 30 ppm, the cubic rate decreases, which is not desirable. It is preferably 10 to 20 ppm.

Cu: 20-80 ppm
Pb: 0.6 to 1.5 ppm
Cu and Pb are important components that determine the solubility of the aluminum foil. Cu is effective in increasing the number of etching pits, and Pb is effective in improving dispersibility of etching pits due to embrittlement of the surface oxide film. By maintaining an appropriate balance between the two components, the number of etching pits can be increased while maintaining a good dispersed state of etching pits, so that a high capacitance can be obtained.

If the Cu content is less than 20 ppm, the number of etching pits decreases, which is not preferable. If it exceeds 80 ppm, the cubic rate decreases, which is not preferable. For this reason, Cu content is defined to the said range. Desirably, the lower limit is 45 ppm and the upper limit is 70 ppm.
Further, when Pb is less than 0.6 ppm, the dispersibility is lowered, so that etching pits are coalesced and the electrostatic capacity is lowered. On the other hand, when Pb exceeds 1.5 ppm, the foil surface is excessively dissolved, so that the capacitance decreases. For this reason, Pb content is defined to the said range. Desirably, the lower limit is 0.8 ppm and the upper limit is 1.2 ppm.

(Zr, V, Mn, Zn, Ga, Na) of one or two or more in total 10 to 50 ppm
Zr, V, Mn, Zn, Ga, and Na are all elements that contribute to an increase in etching pits and an improvement in dispersibility, and contain one or more. However, when the total amount is less than 10 ppm, the effect cannot be obtained, which is not preferable. On the other hand, when the total amount exceeds 50 ppm, the capacitance decreases due to excessive dissolution of the foil. For this reason, the total content of the above components is set within the above range. Desirably, the lower limit is 20 ppm and the upper limit is 45 ppm.

REM: 0.1 to 10 ppm
REM is an element that promotes the precipitation of Fe and increases the bulk aluminum purity to increase the cubic rate. However, if it is less than 0.1 ppm, the effect is not obtained, and if it exceeds 10 ppm, coarse crystals are generated, which is not preferable. For this reason, the content of REM is determined within the above range. Desirably, the lower limit is 1 ppm and the upper limit is 7 ppm. Note that REM may be La, Ce, Pr, Nd, or the like alone, or a mixture of two or more thereof, and may be added in the form of misch metal.

The foil thickness is 100 μm or more and less than 125 μm. The aluminum foil is limited to a thickness of 100 μm or more and less than 125 μm. When the foil thickness is less than 100 μm, the cubic crystal ratio is lowered, which is not preferable. On the other hand, when the foil thickness is 125 μm or more, coarse crystals are generated and local characteristics are greatly deteriorated. For this reason, the thickness of the aluminum foil is determined as described above. Preferably, the lower limit is 110 μm and the upper limit is 120 μm.

Temperature increase rate during final annealing: 30 to 100 ° C./Hr
The rate of temperature rise is a factor that controls element movement and oxide film growth. When the rate of temperature increase is less than 30 ° C./Hr, the annealing time becomes long, which is not industrially preferable. When it exceeds 100 ° C./Hr, sufficient surface concentration cannot be performed, and preferable characteristics cannot be obtained. For this reason, desirably, the rate of temperature increase during the final annealing is set in the above range. More desirably, the lower limit is 40 ° C./Hr and the upper limit is 80 ° C./Hr.

Surface oxide film thickness: 20-100mm
It is desirable to control the surface oxide film after annealing to 20 to 100 mm. When the thickness is less than 20%, the corrosion resistance of the foil is lowered, the storage stability of the annealed foil is deteriorated, and abnormal causes such as surface oxidation are caused. On the other hand, when the thickness exceeds 100%, uniformity is reduced during etching, which causes a reduction in capacity. For this reason, it is desirable that the surface oxide film thickness after annealing be in the above range. More desirably, the lower limit is 40 mm and the upper limit is 60 mm.

Annealing atmosphere In order to set the annealing speed and oxide film thickness within appropriate ranges, it is necessary to appropriately select the atmosphere during annealing.
In vacuum annealing, the heat conduction during annealing is significantly deteriorated, so that the rate of temperature rise is reduced. Furthermore, since the oxide film on the foil surface layer becomes thin, it is not preferable. In the case of atmospheric annealing, the oxide film on the foil surface layer becomes thick and the etching property is lowered, which is not preferable. In the case of an inert gas atmosphere such as Ar and N ₂ , an appropriate oxide film can be formed by controlling the dew point and the oxygen partial pressure, but in order to set the annealing rate within a predetermined range, the aluminum foil to be annealed It is necessary to consider the shape, quantity, etc. Industrially, when annealing a coiled aluminum foil in units of Ton, it is desirable to perform with hydrogen gas. This is because the thermal conductivity is high, so that a sufficient annealing rate can be obtained, and since it is a reducing atmosphere, the growth of the oxide film can also be suppressed. However, by selecting appropriate conditions for the reducing gas, the targets of the annealing rate and the oxide film thickness can be achieved, and thus are not excluded. The atmosphere may be a mixture of a reducing gas and an inert gas. In vacuum annealing and atmospheric annealing, the target of annealing speed and oxide film thickness cannot be achieved.

Final annealing: 500 ° C. or more, 6 hours or more If the final annealing temperature is less than 500 ° C. or the annealing time is less than 6 hours, it is difficult to make the cubic rate of the aluminum foil 95% or more, and the surface of the additive element Is not fully concentrated. For this reason, it is preferable that final annealing shall be 500 degreeC or more and 6 hours or more.

Intermediate annealing: 200 to 280 ° C., 2 to 10 hours Intermediate annealing can be performed in the middle of the cold rolling process for producing the aluminum foil.
This intermediate annealing can promote the formation of cubic crystals.
However, if the intermediate annealing temperature is less than 200 ° C. or the intermediate annealing time is less than 2 hours, the formation of cubic crystals is insufficient, and the cubic crystal ratio after the final annealing is lowered. On the other hand, when the intermediate annealing temperature exceeds 280 ° C. or the intermediate annealing time exceeds 10 hours, crystal grains other than cubic crystals are generated, so that the cubic crystal ratio after the final annealing is lowered.

  As described above, according to the method for producing an aluminum foil for electrolytic capacitors of the present invention, by mass ratio, Si 10 to 30 ppm, Fe 10 to 30 ppm, Cu 20 to 80 ppm, Pb 0.6 to 1.5 ppm, (Zr, V, Mn, Zn, Ga, Na) are contained in a total of 10 to 50 ppm, REM 0.1 to 10 ppm, with the balance being composed of inevitable impurities and 99.9% or more of Al. Aluminum foil with a thickness of 100 μm or more and less than 125 μm is subjected to final annealing at 500 ° C. or more for 6 hours or more in an atmosphere of inert gas, reducing gas or mixed gas thereof, so that pits are generated effectively and uniformly during etching. Thus, the roughening rate can be improved.

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 is prepared. The aluminum material preferably has a purity of 99.95% or more. The aluminum material can be obtained by a conventional method, and the production method is not particularly limited in the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used, and a high-purity aluminum material obtained by continuous casting can also be used. 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 having a thickness of 100 μm to less than 125 μm. In addition, degreasing may be appropriately added during the cold rolling or after the end of the cold rolling, and intermediate annealing at 200 to 280 ° C. for 2 to 10 hours may be appropriately added during the cold rolling.

After the final cold rolling, a final annealing heat treatment is performed. The heating conditions for the final annealing are important for concentrating the above-described additive elements and obtaining a cubic crystal ratio of 95% or more, and a reducing atmosphere using H ₂ or the like, or inert such as Ar or N ₂ In an atmosphere or a mixed gas atmosphere thereof, heating is performed at a temperature rising rate of at least 30 to 100 ° C./hour between 300 to 450 ° C., and heating is performed at 500 ° C. or more for 6 hours or more to obtain an average thickness of 20 to An aluminum alloy foil having a 100-mm oxide film is obtained.
In a reducing atmosphere, it is possible to use a mixed gas obtained by mixing a reducing gas such as H ₂ with an inert gas or a small amount of oxygen. The cubic rate is preferably 95% or more. The said additional element concentrates on a surface layer part by the said annealing. When annealing is performed under vacuum, an oxide film is not properly formed on the surface, and good etching becomes difficult during etching.

  The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. In the present invention, the type of the electrolytic solution is not particularly limited. The etching process can be performed by a surface layer portion removing process, an etching pit generating process, and an etching pit hole diameter expanding process. The surface layer portion removing step is performed by dissolving the surface layer portion including the oxide film. After removing the surface layer portion, an etching pit generation step is performed for generating etching pits on the surface of the aluminum foil. After the etching pit generation process, an etching pit hole diameter expanding process is performed. After this foil is subjected to chemical conversion treatment to obtain a required withstand voltage, a capacitor having a high capacitance can be obtained by incorporating it as an electrode (anode) in an electrolytic capacitor by a conventional method.

An embodiment of the present invention will be described below.
A 4N purity aluminum ingot was used and adjusted to the components shown in Table 1 (others: inevitable impurities + 99.9% or more Al), and then an aluminum slab was prepared by a semi-continuous casting method. In addition, as the REM in the component, a misch metal having a composition of (La: 20 wt%, Ce: 50 wt%, Pr: 5 wt%, Nd: 25 wt%) was used.
The slab was subjected to soaking at 580 ° C. for 2 hours or more, and then hot rolled. At that time, the finishing temperature was 230 ° C. to 350 ° C., and the processing rate was 90% or more. After hot rolling, cold rolling was performed. At that time, intermediate annealing was performed at 150 ° C. to 280 ° C. for 2 to 15 hours, and further cold working of 10 to 20% was performed to obtain an aluminum foil. In addition, the intermediate annealing was performed at a stage where the processing rate in cold rolling was 95% or more.

After the obtained aluminum foil was annealed under the conditions shown in Table 2, pit generation etching was performed by applying a direct current of 300 mA / cm ² for 120 sec in 1M hydrochloric acid + 3M sulfuric acid at 80 ° C. After performing pit generation etching, the pit diameter was expanded by dipping in the same solution for 20 min. The obtained etching foil was formed at 300 V, and the capacitance was measured. The electrostatic capacity is the test material No. 9 was taken as 100, and was shown by relative evaluation.
Further, the obtained test specimen, measuring the oxide film thickness by ESCA (X-ray photoelectron spectrometer), Cube etchant (35% HCl: 60% HNO 3: purified water = 1: 1: 1), 30 The cubic rate was measured by image analysis after immersion at 30 ° C. for 30 seconds, and the results are shown in Table 2. Moreover, after immersing a specimen having a width of 500 mm and a length of 30 cm for 30 seconds at 30 ° C. in a Cube etching solution, coarse crystals were visually evaluated. In this patent, an abnormal crystal grain of 5 mm × 5 mm or more is regarded as a coarse crystal.

Claims (5)

  By mass ratio, Si 10-30 ppm, Fe 10-30 ppm, Cu 20-80 ppm, Pb 0.6-1.5 ppm, (Zr, V, Mn, Zn, Ga, Na) one or two or more in total 10-50 ppm, An aluminum foil for electrolytic capacitors, characterized by containing REM 0.1 to 10 ppm, the balance being an inevitable impurity and 99.9% or more of Al, and having a thickness of 100 μm or more and less than 125 μm.   The aluminum foil for an electrolytic capacitor according to claim 1, wherein the aluminum foil has an oxide film thickness of 20 to 100 mm.   By mass ratio, Si 10-30 ppm, Fe 10-30 ppm, Cu 20-80 ppm, Pb 0.6-1.5 ppm, (Zr, V, Mn, Zn, Ga, Na) one or two or more in total 10-50 ppm, An aluminum foil containing REM 0.1 to 10 ppm, the balance being inevitable impurities and 99.9% or more of Al, and having a thickness of 100 μm or more and less than 125 μm, is made of an inert gas or a reducing gas, or these gases. A method for producing an aluminum foil for electrolytic capacitors, comprising performing final annealing at 500 ° C. or more for 6 hours or more in a mixed gas atmosphere.   The method for producing an aluminum foil for an electrolytic capacitor according to claim 3, wherein a rate of temperature rise during the final annealing is 30 to 100 ° C / Hr.   5. The method for producing an aluminum foil for electrolytic capacitors according to claim 3, wherein intermediate annealing is performed at 200 to 280 ° C. for 2 to 10 hours during cold rolling for producing the aluminum foil.