JP2007191778A - Material for medium and low voltage anode electrolytic capacitor and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil capable of realizing a higher capacitance at a relatively low cost. <P>SOLUTION: The material for a medium and low voltage anode electrolytic capacitor is obtained by casting an aluminum alloy molten metal having an aluminum purity of ≥99.90 mass%, and comprising 50 to 350 ppm Fe, 50 to 350 ppm Si and ≤8 ppm Ti at a cooling rate of ≤1×10<SP>-2</SP>K/s, and is characterized in that the dispersion density of precipitates contained in the aluminum matrix is ≤1×10<SP>-4</SP>pieces/μm<SP>3</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a medium-low voltage anode electrolytic capacitor material and a manufacturing method thereof. In particular, the present invention relates to an aluminum alloy foil used for a medium to low pressure anode electrolytic capacitor.

  The medium / low pressure anodic electrolytic capacitor foil is manufactured by roughening an aluminum or aluminum alloy foil by AC etching and anodizing at a voltage of about 200 V or less. Such an aluminum or aluminum alloy foil for medium- and low-pressure anode electrolytic capacitors is required to have a high capacitance.

  Conventionally, as such an aluminum foil for a medium-low pressure anode electrolytic capacitor, a high-purity aluminum foil in which the amount of Fe and Si, which are inevitable impurities in the aluminum ingot, is minimized (for example, Fe and Si are both 10 ppm or less) Is used. This is because when the Fe and Si contents in aluminum are increased, the foil surface is abnormally dissolved during etching, and the surface area expansion rate cannot be increased, and the capacitance is reduced.

  On the other hand, a high-purity aluminum foil in which the amount of Fe and Si is reduced as much as possible can obtain a high capacitance, but has a problem that the cost becomes very high.

  In this regard, development of an aluminum foil that can achieve a desired capacitance even when Fe and Si are present is underway.

  For example, Fe: 15 to 150 ppm, Si: 15 to 150 ppm, the aluminum purity is 99.96 to 99.994%, and the surface layer from the surface to a depth of 1 μm contains 20 to 200 ppm of Zn. There has been proposed an aluminum foil for a low voltage electrolytic capacitor anode characterized in that the Zn content of the portion other than the above is less than the Zn content of the surface layer and does not exceed 20 ppm (for example, Patent Document 1).

Further, the tensile elongation Y% of a rolled sheet having an aluminum purity of 99.9% by mass or more and containing Fe, Si, Cu and other inevitable impurities and cold-rolled to a rolling rate of 70% or more, electrolyte which satisfies the dispersion density X number / mm ² and is 2 + 0.02X ≦ Y ≦ 4 + 0.02X and 100 ≦ X ≦ 250 crystalliser-precipitates containing the etched before the final foil obtained from rolled plate An aluminum alloy foil for capacitor anode low voltage has been proposed. (For example, patent document 2).

In addition, an intermetallic compound having an aluminum purity of 99.90% by mass or more, containing Fe, Si, Cu, an Fe precipitation amount of 5 ppm or less, and an Si precipitation amount of 5 ppm or less, dispersed in the aluminum matrix. An aluminum alloy foil for a low-pressure anode in an electrolytic capacitor has been proposed (characterized in Patent Document 3, for example), which has a dispersion density of 5 × 10 ⁻⁴ pieces / μm ³ or less.
JP-A-9-129513 JP 2002-151362 A JP-A-9-71832

  However, in any technique, there is still room for improvement in terms of capacitance.

  Accordingly, a main object of the present invention is to provide an aluminum foil capable of realizing a higher capacitance at a relatively low cost.

  As a result of intensive studies in view of the problems of the prior art, the present inventor has found that a specific material can achieve the above object, and has completed the present invention.

That is, the present invention relates to the following materials for medium and low pressure anode electrolytic capacitors.
1. The aluminum purity is 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm and Ti: 8 ppm or less, and the dispersion density of precipitates contained in the aluminum matrix is 1 × 10 ⁻⁴ pieces / A material for medium- and low-pressure anode electrolytic capacitors, characterized by being not more than ³ μm.
2. A method for producing a medium / low pressure anode electrolytic capacitor material, wherein the aluminum purity is 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm and Ti: 8 ppm or less, Hot rolling in which the exposure time at 300 ° C. or higher is within 30 minutes after casting at a cooling rate of 1 × 10 ⁻² K / s or less and homogenizing treatment at a homogenization temperature of 500 ° C. or lower. A method for producing a medium-low pressure anode electrolytic capacitor material, characterized by comprising:

  The material of the present invention is particularly excellent because it is a material produced at a specific alloy composition and a specific casting speed, and the dispersion density of precipitates (particularly intermetallic compounds) of the material is in a specific range. Effect can be achieved.

  That is, although the material of the present invention contains a relatively large amount of Fe and Si, abnormal dissolution during etching is suppressed or prevented, and as a result, a decrease in capacitance can be suppressed or prevented. . Thereby, the high capacity | capacitance aluminum alloy foil for medium-low pressure anode electrolytic capacitors can be supplied cheaply.

1. Material for medium and low voltage anode electrolytic capacitor The material for medium and low voltage anode electrolytic capacitor of the present invention has an aluminum purity of 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm, and Ti: 8 ppm or less, The dispersion density of the precipitate contained in the aluminum matrix is 1 × 10 ⁻⁴ pieces / μm ³ or less.

  In the material of the present invention, precipitates (dispersed particles) are dispersed in an aluminum matrix. The precipitate usually contains at least one of Fe, Si, Ti and the like, but is not limited thereto. Further, the precipitate is generally present as an intermetallic compound or the like.

The dispersion density of the precipitate is 1 × 10 ⁻⁴ particles / μm ³ or less, and preferably 1 × 10 ⁻⁵ particles / μm ³ or less. When the dispersion density is larger than 1 × 10 ⁻⁴ pieces / μm ^{3, the} compound that becomes the starting point of dissolution at the time of AC electrolytic etching of the aluminum foil increases. Capacity will drop. Although the lower limit of the dispersion density is not limited, it is usually about 1 × 10 ⁻⁶ pieces / μm ³ .

The composition of the material of the present invention will be described in detail in the item of the manufacturing method described later.
2. Method for Producing Medium / Low Voltage Anode Electrolytic Capacitor Material The production method of the material of the present invention is not limited, but can be suitably produced by, for example, the following method. That is, a method for producing a medium-low pressure anode electrolytic capacitor material, wherein the aluminum purity is 99.90 mass% or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm, and Ti: 8 ppm or less. Is cast at a cooling rate of 1 × 10 ⁻² K / s or less and subjected to a homogenization treatment with a homogenization treatment temperature of 500 ° C. or less, and then an exposure time at 300 ° C. or more is set to be within 30 minutes. It can be obtained by a production method that performs hot rolling. In the present specification, “ppm by weight” is abbreviated as “ppm”.

The aluminum alloy melt used as the aluminum alloy melt starting material has an aluminum purity of 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm, and Ti: 8 ppm or less. Hereinafter, the role of each component will be described. However, in the present invention, since each component acts synergistically, each role is not limited.

  The aluminum purity is 99.90% by mass or more, preferably 99.93% by mass or more. If it is less than 99.90% by mass, it becomes difficult to prevent abnormal dissolution, and a desired capacitance cannot be obtained.

  Fe is in the range of 50 to 350 ppm, preferably 100 to 300 ppm. If it exceeds 350 ppm, the number of precipitates that become the starting point of dissolution during AC electrolytic etching of the aluminum foil increases, so the amount of dissolution that does not contribute to the increase in capacitance increases, the capacitance decreases, and the strength of the etched foil Will fall. On the other hand, when the concentration is less than 50 ppm, AC electrolytic etching cannot be performed with high efficiency, and as a result, the capacitance decreases.

  Si is 50 to 350 ppm, preferably 100 to 300 ppm. As in the case of Fe, if it exceeds 350 ppm, the number of precipitates that become the starting point of dissolution at the time of AC electrolytic etching of the aluminum foil increases, so the amount of dissolution that does not contribute to the increase in capacitance increases, and the capacitance decreases. The strength of the etched foil is reduced. On the other hand, when the concentration is less than 50 ppm, AC electrolytic etching cannot be performed with high efficiency, and as a result, the capacitance decreases.

  Ti is 8 ppm or less, preferably 5 ppm or less. If it exceeds 8 ppm, an etching failure occurs during AC electrolytic etching and the entire surface is melted, so that the capacitance decreases. The lower limit of the Ti content is not limited, but is usually about 2 ppm.

In addition, as a method of reducing Ti content, there exists B (boron) process of molten aluminum alloy (for example, refer Unexamined-Japanese-Patent No. 2002-194453). Specifically, an amount of 10 to 200 ppm higher than the chemical equivalent calculated as TiB ₂ is added to the molten aluminum alloy to form a Ti-B compound, which is separated from the molten aluminum alloy. can do.

Casting of molten aluminum alloy In the present invention, the molten aluminum alloy is cast at a cooling rate of 1 × 10 ⁻² K / s or less (preferably 1 × 10 ⁻³ K / s or less). When the cooling rate exceeds 1 × 10 ⁻² K / s, the solidification rate of the ingot is increased and the fine intermetallic compound is increased, so that a desired intermetallic compound dispersion density cannot be obtained. Moreover, since the compound used as the starting point of melt | dissolution at the time of the alternating current electrolytic etching of aluminum foil increases, melt | dissolution which does not contribute to the increase in an electrostatic capacitance increases, and an electrostatic capacitance will fall.

  In general, the cooling rate can be represented by a value calculated based on the following relational expression established between DAS (dendrite arm spacing) and the cooling rate c.

DAS (d) = A × c ⁿ (where d represents dendrite arm spacing, and A and n represent coefficients specific to the alloy system)
The above-mentioned d is a document (Dendrite Arm Spacing Measurement Procedure of the Japan Institute of Light Metals “Dendrite Arm Spacing Measurement Procedure”, “Method of Measuring Dendritic Arm Spacing and Cooling Rate of Aluminum”, Japan Institute of Light Metals, August 20, 1988, pp. 46-52. The value measured in accordance with the intersection method described in). In this method, conditions were set such that the number of fields of view was 3 and the number of intersections was 10.

The above A and n are 33.4 and 0.33, respectively, in the AlFeSi alloy. Therefore, also in the present invention, the above numerical values are used as the AlFeSi-based alloy, d = 33.4 × c ^0.33 is adopted as an approximate expression, and the value obtained based on this approximate expression is set as the cooling rate.

  The means for controlling the cooling rate within the above range (particularly, the method for reducing the cooling rate) can be appropriately determined according to the casting method, the apparatus used, and the like. For example, it is possible to cope with a method of extremely slowing the casting speed (speed at which the mold is lowered), a method of cutting cooling water from the vicinity of the lower part of the mold with a wiper or the like. In this case, the non-uniform surface layer, which is frequently generated by slowing the cooling rate, can be dealt with by increasing the amount of chamfering and removing it.

  The casting of the present invention can be carried out according to a known casting method except that the cooling rate is set in the above range. For example, a DC method (Direct chill casting) or the like can be employed. Therefore, a known casting apparatus can be used. In particular, a casting apparatus provided with a cooling water supply means for cooling the molten metal during casting can be suitably used.

Homogenization treatment method of aluminum alloy ingot The homogenization treatment temperature is set to a range of 500 ° C. or lower. If the temperature exceeds 500 ° C., precipitation proceeds during hot rolling or final annealing after foil rolling, and the number of precipitates that become the starting point of dissolution during AC electrolytic etching of aluminum foil increases, contributing to an increase in capacitance. Dissolution increases and capacitance decreases. Although a minimum is not specifically limited, Preferably it shall be 400 degreeC or more. Further, the treatment time is not particularly limited, but is preferably in the range of 1 to 12 hours.

Method of hot rolling aluminum alloy ingot The exposure time (for example, the time from the start of hot rolling to cooling to 300 ° C.) at 300 ° C. or higher in the hot rolling step is set within a range of 30 minutes or less. The range is preferably within 20 minutes. The temperature range where Fe precipitation occurs is 300 ° C. or higher, and when the exposure time in this temperature range is longer than 30 minutes, precipitation proceeds, and the number of precipitates that become the starting point of dissolution during AC electrolytic etching of the aluminum foil increases. Therefore, dissolution that does not contribute to the increase in capacitance increases, and the capacitance decreases. Other hot rolling conditions are not particularly limited, but the hot rolling start temperature is preferably 350 to 500 ° C, and the hot rolling end temperature is preferably about 200 to 300 ° C.

  In this invention, after performing said hot rolling, it can be set as foil by processing by a well-known method. For example, after hot rolling, an aluminum alloy foil having a predetermined thickness can be obtained by performing cold rolling one or more times. The thickness of the aluminum alloy foil may be appropriately changed according to the use, but is usually about 0.05 to 0.2 mm. Further, heat treatment at 300 ° C. or lower may be performed during or at the end of cold rolling.

  When the aluminum alloy is used for a medium-low pressure anode electrolytic capacitor, a predetermined capacitor foil can be obtained by performing etching (AC etching), anodizing treatment, or the like according to a known method.

  The features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the examples.

<Examples 1-5 and Comparative Examples 6-10>
A molten aluminum alloy having the chemical composition shown in Table 1 was prepared. Subsequently, the ingot was manufactured at the cooling rate shown in Table 1. The ingot was homogenized at the temperature shown in Table 1, and then hot rolled at the exposure time shown in Table 1 to obtain a 6 mm hot rolled plate. The hot-rolled sheet was cold-rolled to obtain a foil with a thickness of 0.4 mm, and subsequently subjected to final foil rolling to obtain a foil with a thickness of 0.1 mm.

The Ti content was controlled by subjecting the molten aluminum alloy to B treatment. The B treatment is performed using an Al—B master alloy so that the B content is larger than the chemical equivalent calculated as TiB ₂ from the Ti content, and the Ti—B compound is precipitated for a long time. Then casting started. In this example, since 20 kg of aluminum ingot having a Ti content of 30 ppm was used, 33 g of Al-4 mass% B base was used so that the B content was 100 ppm higher than the chemical equivalent calculated as TiB _2. The alloy was added.

  The cooling rate was controlled by changing the casting speed (speed for lowering the mold).

<Test Example 1>
(Measurement of dispersion density)
About the foil obtained by the above, the deposit collected by the phenol dissolution method of Japanese Patent Publication No. 7-69322 was observed with the scanning electron microscope, and the dispersion density of the deposit was calculated | required. The results are shown in Table 2.

  The dispersion density was specifically measured and calculated according to the following procedures 1) to 10).

  1) The residue collected by filtration with the phenol dissolution method is observed with a scanning electron microscope (SEM).

  2) Perform image analysis on the SEM photograph. At this time, image analysis is performed so as to include 50 or more precipitated particles.

  3) Let n be the number of particles counted in the image analysis.

4) the 3) to measure the diameter _{d n} of the precipitated particles by an image analysis, assuming precipitated particles with a spherical volume _V n of the precipitated particles ^{(= 4πr 3/3, r} = d n / 2) is calculated.

5) The total volume ΣV _n of the volume V _n is divided by the number of particles n to obtain an average volume V ′ per precipitated particle.

6) The weight (m _Al3Fe ) of Al ₃ Fe having an average volume _{V ′} is represented by the following formula from the relationship of (volume = mass / specific gravity):
m _Al3Fe = _{V ′} × _ρAl3Fe ( _ρAl3Fe = 3.84 g / cm ³ )
Calculated by

7) The weight of Fe contained in m _Al3Fe (m _Fe ) is calculated in consideration of the atomic weight.
_{m Fe} = m _Al3Fe × 0.4083
This is the average weight of Fe per precipitated particle.

  8) The amount of Fe precipitation (μg / g) in Al unit g is obtained. That is, the Al weight before dissolution is measured, and the result of ICP emission analysis of all residues collected by filtration by the phenol dissolution method is divided by the Al weight.

9) Al unit volume = Al unit g / Al specific gravity → Al unit g / Al unit volume = 2.7 From the amount of Fe in the Al unit volume, Fe precipitation amount (μg / g) × 2.7 is obtained.

  10) The dispersion density is calculated based on the results of 7) and 9).

Number of precipitate particles in unit volume = weight of Fe in unit volume (b) / average weight of Fe per precipitate (a)
<Test Example 2>
(Measurement of capacitance)
The foils obtained in each Example and Comparative Example were immersed in an etching solution at 55 ° C. (mixed aqueous solution of 5 vol% hydrochloric acid and 0.5 vol% phosphoric acid) for 3 minutes while giving an alternating current of 60 Hz and 8 A / dm ^2. Etched. Thereafter, the aluminum foil was immersed in an anodizing solution (5 wt% ammonium adipate aqueous solution) at 60 ° C. and anodized at 25 V, and the capacitance was measured using an LCR meter. As a result, a relative comparison was made by setting the capacitance of an aluminum containing Fe: 10 ppm and Si: 10 ppm with a purity of 99.99 mass% (for performance standards, No. 6) as 100%. The results are shown in Table 2.

  As is apparent from Table 2, the medium / low pressure anode electrolytic capacitor material produced under the production conditions of the present invention is a medium / low pressure anode electrolytic capacitor material having a high capacitance because abnormal dissolution during etching is suppressed or prevented. It was confirmed that there was.

  As described above, in the present invention, a medium-low pressure anode electrolytic capacitor material having a high capacitance can be obtained. In particular, according to the present invention, no. It can be seen that a high capacitance can be achieved even when Fe or Si exceeds 150 ppm (or more than 200 ppm) as in 3-5.

Claims (2)

The aluminum purity is 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm and Ti: 8 ppm or less, and the dispersion density of precipitates contained in the aluminum matrix is 1 × 10 ⁻⁴ pieces / A material for medium- and low-pressure anode electrolytic capacitors, characterized by being not more than ³ μm. A method for producing a medium / low pressure anode electrolytic capacitor material, wherein the aluminum purity is 99.90% by mass or more, Fe: 50 to 350 ppm, Si: 50 to 350 ppm and Ti: 8 ppm or less, Hot rolling in which the exposure time at 300 ° C. or higher is within 30 minutes after casting at a cooling rate of 1 × 10 ⁻² K / s or less and homogenizing treatment at a homogenization temperature of 500 ° C. or lower. A method for producing a medium-low pressure anode electrolytic capacitor material, characterized by comprising: