JPWO2009063532A1 - Aluminum etched plate for electrolytic capacitors - Google Patents

Abstract

When manufacturing an aluminum etched plate for electrolytic capacitors that has a high etching magnification and can obtain a high capacitance even when impregnated with a solid electrolyte, an alternating current is applied to an aluminum plate with an aluminum purity of 99.98% by mass or more. The aluminum etching board (1) for electrolytic capacitors whose bulk specific gravity of an etching site | part (3) is 0.6-1.2 is obtained by performing electrochemical etching by. The etching site (3) has a pit number of 0.01 to 1 μmφ in the measurement plane when converted into a circle on each measurement surface when a planar cross section at a position deeper than 20 μm from the surface is measured with an image analyzer. 70% or more of the total number of pits is high, the etching magnification is high, and a high capacitance can be obtained even when impregnated with a solid electrolyte.

Description

  The present invention relates to an aluminum etched plate for electrolytic capacitors obtained by etching an aluminum plate.

  In recent years, as electronic devices such as personal computers and information devices have become more digitized and higher in frequency, electrolytic capacitors are required to have lower ESL and higher capacity in addition to lower height, lower impedance, and lower ESR. ing. Electrolytic capacitors are being developed to meet these requirements, but lowering the impedance and lowering the ESR of electrolytic capacitors is a technology that fills (impregnates) a solid electrolyte such as a functional polymer or a solid electrolyte at the etching site. The burden on is large. For this reason, conventionally, for example, an aluminum foil having a thickness of 70 to 120 μm is etched to a depth of about 30 to 35 μm. If this depth is used, a conventional solid electrolyte or Even in the impregnation technique, no major problem has occurred regarding the impregnation property.

  However, an electrode foil etched to a depth of about 30 to 35 μm with respect to an aluminum foil having a thickness of 70 to 120 μm cannot provide a sufficient capacitance. For this reason, when manufacturing an electrolytic capacitor, a plurality of electrode foils are laminated and used, resulting in an increase in manufacturing cost and an increase in the thickness of the electrolytic capacitor, thereby reducing the height. Can not.

Therefore, it has been proposed to increase the electrostatic capacity and reduce the number of laminated electrode foils by thickening the aluminum foil and etching deeply (see Patent Document 1).
JP 2005-150705 A

  However, when the aluminum foil is thickened by the method described in Patent Document 1 and the etching site is deepened, the etching site is not sufficiently impregnated with the solid electrolyte, and sufficient electrostatic capacity cannot be obtained even when the etching magnification is high. There is a problem. In addition, if the etching site is not sufficiently filled with the solid electrolyte, there is a problem that ESR increases.

  In view of the above problems, an object of the present invention is to provide an aluminum etched plate for electrolytic capacitors that has a high etching magnification and can obtain a high capacitance even when impregnated with a solid electrolyte. .

  The inventors of the present application pay attention to the volume weight of the etching site as a parameter that can accurately define the conditions that the etching magnification is sufficiently high and the impregnation rate is sufficiently high, and by setting such a value within a predetermined range, Provided is an aluminum etched plate for electrolytic capacitors, which can obtain a high capacitance even when impregnated with an electrolyte. In this specification, “aluminum etched plate” refers to a sheet having a thickness of 150 μm or more.

  That is, the present invention is characterized in that the bulk specific gravity of the etched portion is 0.6 to 1.2 in an aluminum etched plate for electrolytic capacitors obtained by expanding an aluminum plate by electrochemical etching with alternating current.

  In the present invention, when the aluminum plate is electrochemically etched by alternating current, several thousand to several hundreds of thousands of spongy pits are drilled per square millimeter by etching, and the bulk specific gravity of the etched portion is 0.6 to 1.2. Therefore, since it has a sufficient surface area and the impregnation property of the solid electrolyte is good, a high capacitance can be obtained even when impregnated with the solid electrolyte.

The electrostatic capacity when impregnated with the solid electrolyte cannot be sufficiently defined only by the etching magnification for the following reasons. The etching magnification can be obtained by anodizing the aluminum etched plate for electrolytic capacitors and then measuring the capacitance in an aqueous solution of ammonium adipate. However, the capacitance after the anodization of the aluminum etched plate for electrolytic capacitors and the impregnation with the solid electrolyte (capacitance when used in the electrolytic capacitor) depends on the etching magnification and the impregnation property of the solid electrolyte. Dominated, roughly the following values Etching magnification x Solid electrolyte impregnation (impregnation rate)
Is proportional to The impregnation rate is also referred to as a capacity appearance rate, and indicates to what level the electrostatic capacity measured in the ammonium adipate aqueous solution appears in the state impregnated with the solid electrolyte.

  In general, when the amount of etching electricity is small, the etching is shallow, but the solid electrolyte is easily filled, but the etching magnification is low. On the other hand, when the amount of etching electricity is large, the etching magnification increases as the etching becomes deeper, while the solid electrolyte becomes difficult to be fully filled, so that the impregnation rate tends to decrease. Therefore, when the capacitance after impregnation with the solid electrolyte is high even if the impregnation property is high, the high capacitance cannot be obtained after impregnation with the solid electrolyte, and the etching magnification is high. However, even when the impregnation rate is low, a high capacitance cannot be obtained.

  In addition, when the amount of electricity for etching or the amount of etching reduced from the state of the aluminum plate is specified, the three-dimensional shape of the etched part cannot be sufficiently specified, and the electrostatic capacity after impregnation with the solid electrolyte is sufficiently controlled. Can not. For example, when a large number of fine pits are formed, the etching magnification is increased, but the solid electrolyte is difficult to be fully filled, so that the impregnation rate is lowered. Can't get. On the other hand, when a large number of large pits are formed, the solid electrolyte is easily filled, but since the etching magnification is low, a high capacitance cannot be obtained after impregnating the solid electrolyte.

  However, in the present invention, since it is defined by the bulk specific gravity of the etching site, the three-dimensional shape of the etching site can be defined reliably, and the capacitance after impregnation with the solid electrolyte can be controlled reliably.

  Here, the relationship between the bulk specific gravity of the etching site, the etching magnification, the impregnation rate, and the electrostatic capacity when impregnated with the solid electrolyte is shown by a dotted line L1, a one-dot chain line L2, and a solid line L3 in FIG. As can be seen from this figure, as the bulk specific gravity of the etched portion increases, the etching magnification increases (see the dotted line L1), but the impregnation rate decreases (see the alternate long and short dash line L2), so that the solid electrolyte is impregnated. The capacitance changes as indicated by the solid line L3. That is, when the bulk specific gravity of the etching site is less than 0.6, the solid electrolyte is easily filled, but when the etching magnification is low, and when the bulk specific gravity of the etching site exceeds 1.2, the etching magnification is high, but the solid electrolyte is difficult to fill deeply. Become. Therefore, it is important that the bulk specific gravity of the etching site is 0.6 to 1.2.

  In the present invention, the thickness (depth) of the etching site is 100 μm or more, preferably 120 μm or more. According to such a configuration, the etching magnification is high, and there are deeply etched portions where the solid electrolyte is easily filled to the back, so that the capacitance after impregnation with the solid electrolyte is high.

  The aluminum etched plate for electrolytic capacitors to which the present invention is applied is used as an anode of an aluminum electrolytic capacitor in which a functional polymer is used as an electrolyte. That is, the aluminum etched plate for electrolytic capacitors to which the present invention is applied is used for an electrolytic capacitor in which a dielectric film is formed on the surface and a functional polymer layer is formed on the dielectric film.

It is explanatory drawing which shows the relationship of the electrostatic capacitance at the time of impregnating the volume weight of the etching site | part in the aluminum etched plate for electrolytic capacitor electrodes to which this invention is applied, an etching magnification, an impregnation rate, and a solid electrolyte. It is a figure showing the cross-sectional photograph of the aluminum etched board for electrolytic capacitor electrodes to which this invention is applied. It is explanatory drawing when manufacturing an electrolytic capacitor using the aluminum etched plate for electrolytic capacitor electrodes to which the present invention is applied.

Explanation of symbols

1 Aluminum Etched Plate for Electrolytic Capacitor 2 Core 3 Etching Site

  Hereinafter, as an embodiment of the present invention, a configuration and a manufacturing method of an aluminum etched plate for electrolytic capacitors to which the present invention is applied will be described.

  In the present invention, an aluminum etched plate for electrolytic capacitors obtained by expanding an aluminum plate by electrochemical etching with alternating current has a bulk specific gravity of 0.6 to 1.2 at an etching site. The thickness of the etching site is preferably 100 μm or more, more preferably 120 μm or more.

  The aluminum etched plate for electrolytic capacitors according to this embodiment is formed by etching an aluminum plate having an aluminum purity of 99.98% by mass or more. By using an aluminum plate having such a purity, the toughness is high, and handling when manufacturing an electrolytic capacitor is facilitated. If the aluminum purity is less than the lower limit, the hardness increases, the toughness decreases, and damage such as cracking may occur during handling, which is not preferable.

  The thickness of the aluminum plate used for the etching treatment may be various depending on the purpose. For example, a thickness of 150 μm to 1 mm, usually 300 to 400 μm is used. Then, AC etching is performed on the aluminum plate with a low concentration hydrochloric acid aqueous solution as a primary electrolytic treatment. As a pretreatment, it is preferable to remove the surface oxide film from the aluminum plate by degreasing and light etching.

The low concentration hydrochloric acid aqueous solution used as the electrolytic solution in the primary electrolytic treatment is, for example, an aqueous solution containing 1.5 to 2.5 mol / liter hydrochloric acid and 0.05 to 0.5 mol / liter sulfuric acid as a ratio. 40 to 55 ° C, frequency is 10 to 25Hz, AC waveform is sine waveform, rectangular waveform, AC / DC superimposed waveform, etc., current density is 40 to 50A / dm ² , processing time is 30 to 60 seconds, etching treatment, aluminum A large number of pits are drilled on the plate surface.

After performing the primary electrolytic treatment, the main electrolytic treatment is performed to make holes in a spongy manner, and the etching proceeds. The electrolytic solution used in this main electrolytic treatment is, for example, in an aqueous solution containing 4 to 6 mol / liter hydrochloric acid and 0.05 to 0.5 mol / liter sulfuric acid as a ratio, under the following conditions, that is, the liquid temperature is lower than that of the primary treatment. to 35 ° C., a frequency is 30 Hz to 60 Hz, the AC waveform is a sine waveform, square waveform, such as AC-DC superimposed waveform, the current density may be treated to the primary electrolytic lower than the processing 20~30A / dm ^2, treatment time predetermined etching region thickness The time is set, and the pits drilled by the primary electrolytic treatment are further drilled. By adopting such a method, it is possible to reduce the dissolution that does not contribute to the formation of pits on the surface of the aluminum plate, and to form a spongy etching site in which a large number of pits having a specific size are drilled.

After performing the primary electrolytic treatment, use the AC / DC superimposed waveform to ensure that the main electrolytic treatment proceeds before the main electrolytic treatment, and activate the pit surface drilled by the primary electrolytic treatment before moving to the main electrolytic treatment You may let them. In this process, the etching process is performed for about 60 seconds under the condition that the duty ratio is about 0.7 to 0.9 and the current density is 12 to 17 A / dm ² . By using such an electrolytic etching method, a spongy etching site having a thickness of 70 μm or more, preferably 100 μm or more can be formed.

  Here, if the bulk specific gravity of the etching site is 0.6 to 1.2, an etching site having the following pit diameter and number is formed. The diameter and number of pits can be measured with an image analyzer. That is, after polishing the etched surface at predetermined intervals in the depth direction, by measuring the hole diameter and number of each polished surface with an image analyzer, by calculating the ratio of the number of pits of 0.01-1 μmφ, The proportion of pits having a specific size diameter in each layer can be measured, and in the present invention, it can be determined that a large number of pits having a specific size diameter are perforated uniformly with respect to the etching site. That is, at least one side has an etching part of 70 μm or more, 100 m or more, and further 120 μm or more in the depth direction from the surface, and the number of pits of 0.01 to 1 μmφ measured on the plane section with an image analyzer is all pits on each surface It is possible to obtain for the first time an aluminum etched plate for electrolytic capacitors that is 70% or more of the number, preferably 75% or more. By using such an aluminum etched plate for electrolytic capacitors, an electrolytic capacitor having a low ESR can be realized. Can do. Since the pits of less than 0.001 μmφ do not contribute to the improvement of the capacitance, the diameter measured by the image analyzer is set to 0.001 μmφ or more.

  With respect to the thickness of the etching site, at least one side, preferably each side of both sides, an etching site of 70 μm or more, preferably 100 μm or more, more preferably 120 μm or more is formed in the depth direction from the surface. Preferably, when the thickness of the etching site is less than the above value, it is necessary to increase the number of stacked layers in consideration of the capacitance, and the electrolytic capacitor cannot be reduced in size.

  If there are many pits with a pit diameter exceeding 1 μmφ, the capacitance is lowered. Preferably it is 0.1 μmφ or less. The presence of such sized pits is 70% or more, preferably 75% or more of the total number of pits on each surface, so that an electrolytic capacitor with low ESR can be manufactured. More preferably, it is 80% or more.

  The measurement position of the pit of a specific size is a position deeper than 20 μm from the surface because there is dissolution that does not contribute to the surface area expansion at the time of electrolytic etching near the surface, and the pit diameter is increased by connecting the pits. Further, since the boundary surface between the etching part and the core part is uneven and is not constant, the etching depth is set to a position 10 μm shallower from the position (between the etching part and the core part) on the surface.

  The solid electrolyte is not particularly limited and may be a known solid electrolyte. For example, polypyrrole, polythiophene, polyaniline and the like can be used.

Further, the aluminum purity of the aluminum etched plate for electrolytic capacitors to which the present invention is applied is 99.98% by mass or more, and the number of Fe-containing intermetallic compounds having a particle diameter equivalent to a sphere of 0.01 to 1.0 μmφ is 1 × 10 ⁷ to 10 When it contains ^{10 3} / cm ³ , not only can the ratio of the pits of the specific size diameter be increased, but a capacitor with a lower ESR can be manufactured. This is presumably because the chemical conversion film is formed with a uniform thickness on the pit surface and is easily impregnated with the solid electrolyte because the particle size is small for a large amount of intermetallic compounds.

  The aluminum plate having an aluminum purity of 99.98% by mass or more is not limited in its content as an element other than Al, but as a preferred composition, for example, Fe50ppm or less, preferably 40ppm or less, Cu40ppm or less, Si60ppm or less Preferably, it is 40 ppm or less. This is because when Fe and Si exceed the upper limit values, crystallized substances and precipitates of coarse intermetallic compounds containing Fe and Si are generated, and the leakage current increases. In the case of Si, simple Si is also generated, which is not preferable for the same reason. If Cu exceeds the upper limit value, the corrosion potential of the matrix is greatly changed and no good etching may be performed.

In contrast, 5-50pppm of Fe is contained in metals such as Al _m Fe, Al ₆ Fe, Al ₃ Fe, Al-Fe-Si, Al- (Fe, M) -Si (M is other metals) It is preferable because an intermetallic compound is generated and tends to be a pit starting point for AC etching. The Cu content of 5 to 40 ppm is preferable because the corrosion potential of the matrix can be stabilized in the presence of Fe, and pits of a specific size can be easily formed. As other elements, Ni, Ti and Zr are each 10 ppm or less, preferably 3 ppm or less. Further, other impurities are preferably 3 ppm or less. As a result, it becomes easy to drill pits having a specific size in a spongy shape because they are the starting point of pits in the AC etching method.

Therefore, the aluminum plate has an aluminum purity of 99.98% by mass or more and contains Fe 5 to 50 ppm and Cu 5 to 40 ppm, the balance is inevitable impurities, and the particle size when converted to a sphere is 0.01 to 1.0 μmφ Fe. The contained intermetallic compound is preferably contained in a number of 1 × 10 ⁷ to 10 ¹⁰ / cm ³ .

  Such high-purity aluminum is produced by refining electrolytic primary metal. As a purification method used at this time, a three-layer electrolytic method or a crystal fractionation method is widely employed, and most of elements other than aluminum are removed by these purification methods. However, for Fe and Cu, since it can be used as a trace alloy element rather than as an impurity, the content of each element after purification is measured, and when the content of Fe and Cu is less than a predetermined amount, during slab casting, The content of Fe or Cu can be adjusted by adding Al—Fe, Al—Cu master alloy or the like to the molten metal.

In order to obtain an aluminum plate containing 1 × 10 ⁷ to 10 ¹⁰ / cm ³ of Fe-containing intermetallic compound having a particle size equivalent to a sphere and having a diameter of 0.01 to 1.0 μmφ, for example, the aluminum purity is 99.98% by mass or more Then, after obtaining a slab by semi-continuously casting a molten aluminum with an adjusted Fe content, homogenization at a temperature of 530 ° C. or higher, the range of the plate temperature range where Fe-containing intermetallic compounds are likely to precipitate (300 to And a hot rolled sheet having a number of passes corresponding to (400 ° C.) of 3 times or more, or 30 minutes or more and 60 minutes or less, which is subjected to etching to a predetermined thickness only by cold rolling. In particular, when an aluminum melt having the above composition is cast and rolled as described above, an intermetallic compound having a preferred size and containing a predetermined number of Fe can be easily obtained. The size and number of intermetallic compounds containing Fe can be measured with an image analyzer.

If the particle size of the intermetallic compound containing Fe is equivalent to a sphere and is less than 0.01 μmφ, it tends not to be the core of etching pits by a known method. On the other hand, if it exceeds 1.0 μmφ, the leakage current is likely to be affected when the capacitor is assembled. In addition, if the number of intermetallic compounds containing Fe of 0.01 to 1.0 μmφ in particle size is less than 1 × 10 ⁷ / cm ³ , the proportion of pits of a specific size is small, 1 × 10 ¹⁰ / cm ³ If it exceeds, excessive dissolution increases.

(Example)
FIG. 2 is a view showing a cross-sectional photograph of an aluminum etched plate for electrolytic capacitor electrodes to which the present invention is applied. FIG. 3 is an explanatory diagram when an electrolytic capacitor is manufactured using an aluminum etched plate for electrolytic capacitor electrodes to which the present invention is applied.

  Semi-continuously cast molten aluminum to obtain a slab with a thickness of 560 mm, heated to 550 ° C for 10 hours, uniformly processed, held at 350 ° C for a different holding time, then hot rolled and rolled An aluminum plate having a thickness of 0.4 mm was used. The composition is shown in Table 1.

  Using an aluminum plate having an Al purity of 99.98% by mass or more having a thickness of 0.4 mm, double-side etching was performed under the following conditions to obtain an aluminum etched plate for electrolytic capacitors shown in FIG. The aluminum etched plate 1 for electrolytic capacitors is provided with etching sites 3 on both sides of the core 2.

(Etching conditions)
After mild degreasing with 10% aqueous caustic soda solution, degreasing and removal of surface oxides, as the primary etching treatment, in an aqueous solution containing 2 mol / liter hydrochloric acid and 0.02 mol / liter sulfuric acid as the electrolyte, It was processed at a temperature of 50 ° C., a frequency of 20 Hz, an AC sine wave AC, a current density of 45 A / dm ² , and a processing time of 45 seconds, and many pits were drilled on the aluminum plate surface. Next, in the aqueous solution containing 6 mol / liter hydrochloric acid and 0.05 mol / liter sulfuric acid as the electrolytic solution as the main electrolytic treatment, the liquid temperature is 30 ° C., and the frequency can be arbitrarily set, for example, 50 Hz, sinusoidal alternating current, The current density was 25 A / dm ² , the pits drilled in the primary treatment with various treatment times were further drilled to obtain spongy etched sites of various thicknesses, and the thickness of the etched sites was measured. The results are shown in Tables 2-7.

(Method for measuring bulk specific gravity)
Measure the length, width, etching thickness, core thickness, and total mass of an etched plate (including the central core) etched to various thicknesses. The bulk specific gravity was calculated. The results are shown in Tables 2-7.

(Measurement of pit diameter)
Next, the pit diameter and its ratio were measured with an image analyzer. The measurement is performed by dividing the surface distance between the surface 20 μm from the surface in the etching depth direction of the sample and the position 10 μm shallower from the position where the etching depth is defined (between the etching site and the core) to the surface side by four ( However, the surface corresponding to the five surfaces when the thickness of the etching layer on one side was 35 μm was polished sequentially from the surface, and each surface was measured with an image analyzer. For the pit diameter and its ratio, the average of 10 points on each measurement surface was taken as the value of that measurement surface. Among the measurement results for 2 surfaces or 5 surfaces, Tables 2 to 7 show the values in which the number of pits having a pit diameter of 0.01 to 1 μmφ when converted to a circle accounts for the smallest number of the total number of pits in the measurement surface. Shown in

  Next, the aluminum etched plate for electrolytic capacitors was subjected to 5V chemical conversion treatment in an aqueous solution of ammonium adipate, and then impregnated with polypyrrole according to a conventional method to form a functional polymer layer as shown below. A 330 μF electrolytic capacitor was fabricated, and ESR (100 KHz), capacitance, and leakage current were measured. The results are shown in Tables 2-7.

(Polypyrrole impregnation)
When impregnating with polypyrrole, an ethanol solution of a pyrrole monomer is dropped into the pit, and ammonium persulfate and an aqueous solution of sodium 2-naphthalenesulfonate are dropped and chemically polymerized to form a precoat layer made of polypyrrole. Next, this electrode plate was immersed in an acetonitrile electrolyte containing a pyrrole monomer and sodium 2-naphthalenesulfonate, and a stainless steel wire was brought into contact with a part of the previously formed chemically polymerized polypyrrole layer to serve as an anode, Electrolytic polymerization is performed using a stainless steel plate as a cathode to form an electropolymerized polypyrrole that becomes a functional polymer layer. In addition, it can replace with polypyrrole and can obtain an equivalent characteristic even if it uses polythiophene or polyaniline.

(Method for producing electrolytic capacitor)
In order to produce an electrolytic capacitor using the etched aluminum capacitor-etched plate for electrolytic capacitor, as shown in FIG. 3, the aluminum etched plate for electrolytic capacitor 1 having both surfaces etched is subjected to anodic oxidation, followed by electrolysis. The side end face of the capacitor aluminum etched plate 1 is exposed, and an anode lead 6 such as a lead wire is joined to the side end face 4 of the core portion 2. As a joining method, laser welding 5 with a spot diameter reduced to less than the thickness of the core was used. The spot diameter was 20-100φ.

  Next, after forming the functional polymer layer on the surface of the anodized aluminum etched plate 1 for electrolytic capacitors, carbon paste or silver paste is formed on the surface of the etched plate on which the functional polymer layer is formed. The cathode was formed using the above, and the electrode body was constructed, and the ESR (100 KHz), capacitance, and leakage current were measured as described above. The results are shown in Tables 2-7.

  As shown in Tables 2-7, an aluminum capacitor for an electrolytic capacitor having an etched portion with a bulk specific gravity of 0.6 to 1.2, an electrolytic capacitor having a low ESR, a high capacitance, and a low leakage current is obtained. Can do. In addition, even when the thickness of the etching site is large, an electrolytic capacitor having a low ESR, a high capacitance, and a low leakage current can be obtained.

  On the other hand, sample numbers 2-1, 3-1, 4-1, 5-1, 6-1 and 7-1 with large bulk specific gravity have high ESR, low capacitance, and high leakage current. . It can also be seen that Sample Nos. 2-6, 3-6, 4-6, 5-6, 6-6, and 7-6 having a small bulk specific gravity have a low capacitance.

  In the present invention, when the aluminum plate is electrochemically etched by alternating current, several thousand to several hundreds of thousands of spongy pits are drilled per square millimeter by etching, and the bulk specific gravity of the etched portion is 0.6 to 1.2. Therefore, since it has a sufficient surface area and the impregnation property of the solid electrolyte is good, a high capacitance can be obtained even when impregnated with the solid electrolyte.

Claims (5)

In the aluminum etched plate for electrolytic capacitors, which is obtained by subjecting the aluminum plate to electrochemical expansion by alternating current and expanding the surface.
An aluminum etched plate for electrolytic capacitors, wherein the bulk specific gravity of the etched portion is 0.6 to 1.2.   The aluminum etched plate for electrolytic capacitors according to claim 1, wherein a thickness of the etched portion is 100 μm or more.   2. The aluminum etched plate for electrolytic capacitors according to claim 1, wherein the thickness of the etched portion is 120 m or more.   The aluminum etched plate for electrolytic capacitors according to any one of claims 1 to 3, wherein the aluminum etched plate is used as an anode of an aluminum electrolytic capacitor in which a functional polymer is used as an electrolyte.   The dielectric film is formed on the surface subjected to the electrochemical etching, and a functional polymer layer is formed on the dielectric film. Aluminum etched plate for electrolytic capacitor as described.

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