JP2009019248A - Aluminum foil material for electrode of electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil for an electrolytic capacitor, wherein formation of etch pits progresses uniformly and deeply into inner parts of aluminum to yield a high electrostatic capacitance at electrolytic etching by an alternating current without inducing excessive dissolving at the surface or inner parts. <P>SOLUTION: The aluminum foil material for an electrode of the electrolytic capacitor has a composition comprising 30-450 ppm Fe and 30-300 ppm Si and having an Al purity of ≥99.90% and is subjected to an AC etching treatment. Among intermetallic compounds present in the foil material, the ratio I(α-AlFeSi)/I(Al<SB>3</SB>Fe) in an X-ray diffraction pattern of an undissolved residue obtained by a thermal phenol method is 0.15-0.60, provided that I(α-AlFeSi) is the strength of α-AlFeSi and I(Al<SB>3</SB>Fe) is the strength of Al<SB>3</SB>Fe. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is an aluminum foil material for electrolytic capacitor electrodes, particularly an inexpensive aluminum foil material with a large content of Fe and Si, and a uniform and many pits are formed by an AC etching process, thereby obtaining a high capacitance. The present invention relates to an aluminum foil material for electrolytic capacitor electrodes.

  Along with the miniaturization of electronic components, there is a demand for an improvement in capacitance of the aluminum foil for electrolytic capacitors used in the components by increasing the surface area after the etching process. Etching of aluminum foil for electrolytic capacitors is usually performed by applying an electrochemical or chemical treatment in a solution containing chlorine ions, forming a large number of holes called etch pits, and the surface area of the etched surface. To enlarge.

  The etched etched foil is formed, for example, by anodic oxidation in an aqueous solution of boric acid or ammonium adipate, whereby a dielectric oxide film is formed according to the operating voltage of the capacitor. The capacitance of the capacitor is given by C = εS / d (C: capacitance, ε: dielectric constant of conversion coating, S: surface area, d: thickness of conversion coating).

Conventionally, attempts have been made to identify the type and size of Fe-based intermetallic compounds or the abundance ratio in order to increase the capacitance of aluminum foil for electrolytic capacitors that are subjected to AC etching treatment. Among Al—Fe-based intermetallic compounds, a method of regulating the ratio of Al ₆ Fe / Al ₃ Fe to 0.5 or less (see Patent Document 1), and the major axis of the intermetallic compound in the aluminum foil is less than 0.1 μm Proposed to define the ratio of the Fe content of intermetallic compounds of each size to the Fe content of the entire foil. (See Patent Document 2).

However, as described above, a high electrostatic capacity is obtained only by specifying the ratio and size of the intermetallic compound, Al ₆ Fe, Al ₃ Fe, or the ratio of the Fe content of the intermetallic compound to the Fe content of the entire foil. It is not always sufficient to obtain a capacity, and there is a problem that the electrostatic capacity may decrease due to dissolution on the foil surface or inside during electrolytic etching by alternating current.
JP 2006-144122 A JP 2004-149835 A

  The present invention has been made to solve the above-mentioned conventional problems for increasing the capacitance of aluminum foil for electrolytic capacitors that are subjected to AC etching treatment, and the purpose thereof is the surface and the interior during electrolytic etching by AC. It is an object of the present invention to provide an aluminum foil for electrolytic capacitors in which the formation of etch pits proceeds uniformly and deeply into the aluminum without causing excessive dissolution in the aluminum, and a high capacitance can be obtained.

In order to achieve the above object, an aluminum foil for electrolytic capacitor according to claim 1 contains Fe: 30 to 450 ppm, Si: 30 to 300 ppm, has an Al purity of 99.90% or more, and has an AC etching treatment. The aluminum foil material for electrolytic capacitor electrodes, and among the intermetallic compounds present in the foil material, α-AlFeSi strength I (α-AlFeSi) in the X-ray diffraction pattern of the dissolved residue obtained by the hot phenol method ) And Al ₃ Fe strength I (Al ₃ Fe), I (α-AlFeSi) / I (Al ₃ Fe) is 0.15 to 0.60.

  The aluminum foil material for electrolytic capacitor electrodes according to claim 2 is characterized in that, in claim 1, the amount of Fe existing as an intermetallic compound is 50% or more of the Fe content of the foil material.

  According to the present invention, during electrolytic etching by alternating current, the formation of etch pits proceeds uniformly and deeply inside the aluminum without causing excessive dissolution on the surface and inside, and an aluminum foil for electrolytic capacitors that can obtain a high capacitance. Is provided.

The aluminum foil material for electrolytic capacitor electrodes according to the present invention is an aluminum foil material containing Fe: 30 to 450 ppm, Si: 30 to 300 ppm, having an Al purity of 99.90% or more and subjected to AC etching. Of the intermetallic compounds present in the foil material, α-AlFeSi strength I (α-AlFeSi) and Al ₃ Fe strength I (Al ₃ in the X-ray diffraction pattern of the dissolved residue obtained by the hot phenol method. The ratio of Fe), I (α-AlFeSi) / I (Al ₃ Fe), is 0.15 to 0.60.

In the AC etching process, pits are generated starting from an intermetallic compound in the foil. As a result of investigating the influence of the presence state of the intermetallic compound on the etching behavior in the AC etching process, the inventors found that the abundance ratio of α-AlFeSi and Al ₃ Fe greatly affects the capacitance. As a result of further investigation based on the findings, the present invention has been achieved.

Since Al ₃ Fe is relatively finer than the pit size, it has the most effective action for forming a pit start point during the AC etching process and a defect portion of the cathode film in the pit. α-AlFeSi has a spherical shape and is larger than the size of the pit generated by the AC etching process, causing pit wraparound, forming a missing surface portion on the foil surface layer, and a cavity in the etching layer inside, reducing the capacitance Invite. On the other hand, the solid solution Si causes excessive dissolution of the matrix and lowers the electrostatic capacity due to coalescence of pits in the etching layer.

In the aluminum foil material for electrolytic capacitor electrodes of the present invention containing more Si than ordinary materials, in order to prevent excessive dissolution during etching, a part of Si is α-AlFeSi, and α-AlFeSi or Al ₃ Fe Even in the case of an inexpensive aluminum foil material having a high Fe or Si content, uniform and many pits can be formed by AC etching, and a high capacitance can be obtained.

  The aluminum foil material according to the present invention contains Fe: 30 to 450 ppm and Si: 30 to 300 ppm. When the Fe content and the Si content are less than 30 ppm, the purity becomes high as in the case of conventionally used aluminum foil materials for electrolytic capacitor electrodes. Further preferable Fe content and Si content are 50 ppm or more.

  When the Fe content and the Si content exceed 450 ppm and 300 ppm, respectively, a high capacitance cannot be obtained even if the structure control as in the present invention is performed. Furthermore, the upper limit of preferable Fe content and Si content is 400 ppm and 250 ppm, respectively. The Al purity is preferably 99.90% or more. If the purity is less than 99.90%, there are many impurities, and a high capacitance cannot be obtained. Further preferred Al purity is 99.97% or more.

  As elements other than Si and Fe, Cu is 0.005% or less, Mn, Mg and Cr are 0.001% or less, Zn, Ti, Ga and V are 0.005% or less, respectively, and other inevitable impurities. Even if it contains in 0.001% or less of range, the effect of this invention is not affected.

In the present invention, the strength of α-AlFeSi in the X-ray diffraction pattern of the dissolved residue obtained by the hot phenol method (hot phenol dissolution method) is d = 0.2038 nm, θ = 44.5 deg, and the strength of Al ₃ Fe is d = It is determined from the peak intensity corresponding to 0.2095 nm and θ = 43.14 deg.

The ratio of the intensity of the α-AlFeSi I (α-AlFeSi ) and _Al 3 Fe intensity _{I (Al 3 Fe), I} (α-AlFeSi) / I (Al 3 Fe) is 0.15 to 0.60, When I (α-AlFeSi) / I (Al ₃ Fe) exceeds 0.60, as described above, during AC etching, surface deficiency and internal cavities occur in the etching layer, which is caused by excessive dissolution. A decrease in capacitance occurs. When I (α-AlFeSi) / I (Al ₃ Fe) is less than 0.15, the solid solution Si causes excessive dissolution of the matrix, and the capacitance decreases due to coalescence of pits in the etching layer.

  In order to obtain a high capacitance, the amount of Fe present as an intermetallic compound is preferably 50% or more of the Fe content of the aluminum foil material. More preferably, it is 70% or more, More preferably, it is 80% or more. If the amount of Fe present as an intermetallic compound is less than 50% of the Fe content in the aluminum foil material, the etching layer is likely to be dissolved due to the solid solution of Fe, and it is difficult to obtain a high capacitance.

Hereinafter, the manufacturing method of the aluminum foil material of this invention is demonstrated. In addition, this manufacturing method shows one Embodiment, It is not limited to this manufacturing method.
For example, an ingot having a thickness of 500 mm is formed by semi-continuous casting. In this case, slow cooling is performed at a cooling rate of 3 to 20 ° C./second, more preferably 3 to 10 ° C./second during solidification of the ingot so that α-AlFeSi crystallizes appropriately in the ingot. If the cooling rate is too high, the α-AlFeSi crystallized product becomes excessively fine and is lost during etching, causing a decrease in capacitance. There is also a problem that it becomes easier to re-dissolve.

The ingot is hot-rolled at a starting temperature of 450 to 550 ° C. without performing a homogenization process or without performing a homogenization process at a high temperature so that α-AlFeSi does not re-dissolve. Next, for example, cold rolling is performed at a rolling rate of 98% to obtain a foil material having a thickness of 100 μm. The resulting foil member, composition, depending on the production conditions, subjected to final annealing 5~12h in the temperature range of 280 to 350 ° C., to adjust the intensity and _Al 3 Fe amount.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Examples and Comparative Examples Molten aluminum melts having the compositions shown in Table 1 were ingoted by continuous casting, and the resulting ingots were homogenized, hot-rolled and cold-rolled, or homogeneously under the conditions shown in Table 2 Hot-rolling and cold-rolling were carried out without performing a heat treatment, and a foil having a thickness of 90 μm was obtained. A part of the foil was subjected to a final annealing treatment under the conditions shown in Table 2 in a nitrogen gas atmosphere.

About the obtained aluminum foil material (test material), strength I of α-AlFeSi in the X-ray diffraction pattern of the dissolved residue obtained by the hot phenol method among the intermetallic compounds present in the aluminum foil material by the following method After measuring the ratio of strength I (Al ₃ Fe) between (α-AlFeSi) and Al ₃ Fe, I (α-AlFeSi) / I (Al ₃ Fe), and performing AC electrolytic etching treatment by the following method Then, after chemical conversion to 20 V in an aqueous solution of ammonium adipate, the capacitance was measured with a 120 Hz series equivalent circuit using LCR. The results are shown in Table 3. In Tables 1 and 3, those outside the conditions of the present invention are underlined.

Measurement of I (α-AlFeSi) / I (Al ₃ Fe): Thermal phenol method, that is, the test material is completely dissolved in 100 ml of boiling phenol in the range of 1 to 5 g, and benzyl is used to prevent phenol solidification. Add 50 ml of alcohol. Furthermore, benzyl alcohol is added so that it may become 200 ml on the whole, and it cools to about 85 degreeC, Then, it suction-filters using a membrane filter with the hole diameter of 0.2 micrometer. At the same time as the X-ray diffraction measurement of the obtained residue, the filter residue is dissolved in hydrochloric acid, and the amount of Fe deposited is quantified by atomic absorption spectrometry. Note that ICP emission spectroscopic analysis may be performed instead of the atomic absorption method.

AC electrolytic etching treatment: Using a mixed solution of hydrochloric acid 1.5 mol / dm ³ , phosphoric acid 0.09 mol / dm ³ and nitric acid 0.07 mol / dm ³ , with a liquid temperature of 32 ° C. and a 25 Hz sine wave AC, a current density of 200 mA / Electrolytic treatment is performed at cm ² for 450 s.

  As can be seen from Table 3, each of the test materials 1 to 15 according to the present invention has an excellent capacitance of 98% or more when the capacitance of the test material 1 is 100%.

On the other hand, as shown in Table 3, the test materials 16 and 17 are caused by the fact that the α-AlFeSi crystallized material is excessively refined and missing during etching because the cooling rate during ingot ingot formation is large. As a result, the capacitance decreased. Since the test materials 18 and 19 have a low cooling rate during ingot ingot formation, α-AlFeSi does not crystallize appropriately, and α-AlFeSi strength I (α-AlFeSi) and Al ₃ Fe strength I ( The ratio of Al ₃ Fe), I (α-AlFeSi) / I (Al ₃ Fe), decreases, and the solid solution Si causes excessive dissolution of the matrix, and the capacitance is caused by coalescence of pits in the etching layer. Declined. Since the test material 20 has a large content of Fe and Si and low Al purity, the amount of intermetallic compound is too large. When the ratio of only I (α-AlFeSi) / I (Al ₃ Fe) is regulated, It was not possible to control the weight loss of the solution, and the capacitance was inferior.

Claims (2)

Electrolytic capacitor electrode containing Fe: 30 to 450 ppm (mass ppm, hereinafter the same), Si: 30 to 300 ppm, having an Al purity of 99.90% (mass%, hereinafter the same) or more and subjected to AC etching treatment Aluminum foil material, α-AlFeSi strength I (α-AlFeSi) and Al ₃ Fe in the X-ray diffraction pattern of the dissolved residue obtained by the hot phenol method among the intermetallic compounds present in the foil material An aluminum foil material for an electrolytic capacitor electrode, wherein the ratio of strength I (Al ₃ Fe) of I (α-AlFeSi) / I (Al ₃ Fe) is 0.15 to 0.60. 2. The aluminum foil material for electrolytic capacitor electrodes according to claim 1, wherein the amount of Fe existing as an intermetallic compound is 50% or more of the Fe content of the foil material.