JP2006169571A - Aluminum foil for electrolytic capacitor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum foil for a capacitor mainly used in a middle to high voltage range having high capacitance and high strength, which has cubic crystals at a high rate existing thereon even when having a large thickness, and consequently can make a deep pit formed therein in a thickness direction. <P>SOLUTION: The aluminum foil for an electrolytic capacitor is made from aluminum with a purity of 99.9% or more, has a foil thickness of 0.15 to 0.6 mm, has no coarse crystal grain with a grain size of 5 mm or larger exist thereon, and has a cubic crystal rate of 90% or higher. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure capable of stably obtaining a high cubic crystal ratio without a coarse crystal even in a relatively thick foil thickness of, for example, 0.15 mm or more in an aluminum foil for electrolytic capacitors, and a method for manufacturing the same.

In general, an aluminum electrolytic capacitor is configured such that an anode aluminum foil having an aluminum oxide dielectric film formed on the surface thereof by anodic oxidation and a cathode aluminum foil not subjected to oxidation treatment are opposed to each other with an electrolyte interposed therebetween. As the aluminum foil for the anode, high-purity aluminum having a purity of about 99.99% is usually used, and as the aluminum foil for the cathode, various aluminum alloys having a purity of about 99.2 to 99.8% are usually used. in use.
However, in this type of aluminum electrolytic capacitor, for the purpose of improving its electrostatic capacity, various studies have been made on a small amount of additive elements and manufacturing processes for the anode formed of high-purity aluminum foil. However, not only high pressure but also medium and low pressure electrolytic capacitors are actively used.

Among them, the medium- and high-pressure etching foils for electrolytic capacitors are roughened by making many holes called pits on the surface, and the characteristics have been improved so that high capacity can be obtained. Etching technology is improving year by year. However, recently, the number of pits on the surface has reached a level almost close to the limit, and in the research and development in the direction of simply increasing the number of pits, the limit for high capacity countermeasures is becoming close to the limit. .
Therefore, the present inventor kept the etching foil, which has been recommended to be thinner, in a state that is slightly thicker than before, in order to further increase the capacity, and lengthen the pit, in other words, the pit itself. I think that it is necessary to form deeper than above. Note that if pits deeper than before are formed on the thinned etching foil, the thickness of the aluminum body portion where no pits are formed becomes thinner than before, so in some cases the mechanical strength of the etching foil itself may be reduced. There may be a shortage.

Since the pits formed on the surface of the aluminum foil are perpendicular to the (100) plane of the aluminum crystal, it is necessary to increase the cubic ratio in the aluminum foil crystal in order to obtain high capacity and high strength. There is.
According to the research by the present inventors, in order to grow aluminum cubic crystals, annealing at 200 to 300 ° C. (intermediate annealing) is performed in the middle of cold rolling to grow crystal grains serving as the nucleus of the cubic crystals. After that, rolling (additional rolling) is performed again, and the previous crystal grains are distorted, so that it is necessary to prepare a situation in which cubic crystals preferentially grow during final annealing.
However, when such a manufacturing method is adopted, it is good if the thickness of the aluminum foil is thin. However, if the aluminum foil is made thicker than before, coarse crystal grains (having a diameter of 5 mm or more without a specific orientation). Crystal grains) are easily generated, and it is difficult to form deeper pits uniformly. For example, the current aluminum foil for electrolytic capacitors is often formed thinner than 0.15 mm, but has a high cubic crystal ratio in which no coarse crystal grains are present in an aluminum foil having a thickness of 0.15 mm or more. It has been difficult to obtain the conventional manufacturing technology.

Conventionally, as a technique for obtaining a high cubic crystal ratio, as described in Patent Document 1 below, an aluminum ingot having a desired thickness is manufactured by subjecting an aluminum ingot to hot working and cold working. The hot working rate is set as high as 99.2 to 99.8% and the cold working rate is set as 75 to 97% to obtain a high cubic rate without intermediate annealing. Technology that can do this has been proposed. (See Patent Document 1)
JP 2004-250772 A

However, in the method described in Patent Document 1, the hot working rate is increased so as to be in the range of 99.2 to 99.8%. Since the temperature is lowered, the amount of Fe-based precipitates containing Fe, which is necessarily contained in a small amount of aluminum ingots, is a factor that suppresses crystal grain growth, and coarse crystal grains are likely to be generated. There is a problem, and the technique of Patent Document 1 cannot simply be applied to the previous purpose.
When the above-mentioned coarse crystal grains are precipitated, the crystal orientation in the coarse crystal grain portions is not uniform, so that when pits are generated, the probability that the pits grow obliquely with respect to the thickness direction of the aluminum foil increases. Therefore, when etching is performed, pits are likely to be uneven, which causes local capacity reduction and strength reduction, significantly reducing the quality of the product and eliminating coarse crystal grains as much as possible. There is a need to.
In addition, since the coarse crystal grains are not generated uniformly on the entire surface of the aluminum foil, but tend to be generated locally, the characteristics evaluation of the aluminum foil when the coarse crystal grains are generated is performed in a wide range as much as possible. There is a need.

  The present invention has been made in view of the above circumstances, and even when the thickness of the aluminum foil for capacitors mainly used for medium and high pressure is increased, the ratio of cubic crystals is high, and deep pits can be formed in the thickness direction. Therefore, an object is to provide a high-capacity, high-strength aluminum foil for capacitors.

As a result of studying the present inventors in view of the above-mentioned problems, intermediate annealing is performed by controlling the processing rate and finishing temperature of hot rolling in the process of manufacturing an aluminum foil and further adjusting the foil thickness at the time of final annealing. And it has been found that a high cubic rate can be obtained without additional rolling, and the present invention has been achieved.
To achieve the above object, the present invention provides a foil thickness in the range of 0.15 to 0.6 mm, a purity of 99.9% by mass or more, 5 to 20 ppm by mass of Fe, 5 to 50 ppm by mass of Si, and Cu. 1 to 100 ppm by mass, Pb 0.1 to 5 ppm by mass, the balance being an aluminum foil made of Al and inevitable impurities, and the Pb ionic strength ratio at the depth position of 0.1 μm and the outermost layer And 2.0 or more, there are no coarse crystal grains having a particle diameter of 5 mm or more, and the cubic crystal ratio is 90% or more.
In the present invention, the number of crystal grains is 6000 to 15000 / cm ² , and among these, crystal grains having a diameter of 100 μm or less are preferably 50 to 70% in number ratio.

  The method for producing an aluminum alloy foil for an electrolytic capacitor according to the present invention includes the step of hot rolling an aluminum or aluminum alloy ingot, followed by cold rolling, and an aluminum for electrolytic capacitor having a thickness of 0.15 to 0.6 mm. When manufacturing the foil, the processing rate in the hot rolling is in the range of 95 to less than 99.0%, the temperature at the end of the hot rolling is in the range of 250 to 400 ° C, and the foil thickness is 0.15 to 0.00. After the range of 6 mm, a heat treatment is performed to heat in a range of 530 to 600 ° C.

The matters limited in the present invention will be described below.
The aluminum alloy foil for electrolytic capacitors mainly used for medium to high pressure according to the present invention is mainly composed of 99.9% by mass or more of pure aluminum.
Here, as elements other than Al contained in the alloy foil of the present invention, Fe is in the range of 5 to 20 ppm by mass, Si is in the range of 5 to 50 ppm by mass, Cu is in the range of 1 to 100 ppm by mass, and Pb is 0. .1-5 mass ppm may be contained. Moreover, you may contain about 5-30 mass ppm of other inevitable impurities as a total amount.
Fe: 5 to 20 ppm by mass
Fe is an inhibitor of crystal grain growth in the metal structure of the aluminum foil for electrolytic capacitors. Therefore, it is preferable to contain a trace amount in the above range. On the contrary, if the content is too small, Fe-based Fe containing Fe There arises a problem that the amount of precipitates is reduced and coarse crystal grains are easily generated.
Si: 5-50 ppm by mass
Si combines with Fe to produce precipitates. If it is less than 5 ppm by mass, the amount of precipitates produced is reduced, and it becomes difficult to suppress coarse crystal grains. If it exceeds 50 ppm, the amount of precipitates increases and the growth of cubic crystals is suppressed, resulting in a decrease in cubic rate. Desirably, it is the range of 10-20 mass ppm.
Cu: 1 to 100 ppm by mass
Cu is an element necessary for obtaining moderate solubility, and if it is less than 1 ppm, the amount of dissolution is insufficient and the amount of pit generation is reduced, so that a high capacitance cannot be obtained. If it exceeds 100 ppm, overdissolution occurs, pit coalescence and loss increase, and the capacitance decreases. Desirably, it is the range of 10-60 ppm.
Pb: 0.1 to 5 mass ppm, and an ionic strength ratio between the depth position of 0.1 μm and the outermost layer is preferably 2.0 or more.
Pb is an element that is strongly concentrated in the surface oxide film and has a role of embrittlement of the surface oxide film, and uniform etching cannot be performed unless a certain amount is concentrated. Therefore, the above range is preferable.

Cubic crystal ratio: 90% or more When the cubic crystal ratio is less than 90%, the number of vertically generated pits decreases, resulting in insufficient capacity and strength.
Number of crystal grains: 6000 to 15000 / cm ²
Here, when the number of crystal grains is less than this range, the individual grain sizes become large and coarse crystal grains are likely to be generated. When the number of crystal grains is larger than this range, the individual grain sizes become small, and the cubic rate decreases.

Number of crystal grains with a diameter of 100 μm or less 50-70%
When it is less than this range, large crystal grains increase, so that coarse crystal grains are likely to be generated. When the growth of crystal grains is insufficient, the crystal grains of 100 μm or less exceed 70%. As a result, the cubic rate tends to decrease. If it is less than 50%, the number of crystal grains of 100 μm or more is relatively increased, so that coarse crystal grains are likely to be generated.

According to the present invention, it is possible to provide an aluminum foil for an electrolytic capacitor having a large capacity and high strength, which has many small crystal grain sizes, a high cubic crystal ratio, and capable of forming deep etching pits.
Further, when the manufacturing method as in the present invention is adopted, it is not necessary to selectively add strain to the crystal grains serving as the nucleus of the cubic crystal, so that the abnormal growth of the cubic crystal does not occur, resulting in the generation of coarse crystal grains. I also found that I did not. Therefore, it is possible to obtain an aluminum foil having a high cubic rate without coarse crystal grains.

The aluminum foil for electrolytic capacitors according to the present embodiment is mainly composed of 99.9 mass% or more of pure aluminum, but Fe: 5 to 20 mass ppm, Si: 5 to 50 mass ppm, Cu: 1 to 100 mass. It is a composition containing about 5 to 30 mass ppm of ppm, Pb: 0.1 to 5 mass ppm and other inevitable impurities.
Moreover, the aluminum foil for electrolytic capacitors according to the present embodiment is an aluminum foil made of aluminum having a foil thickness in the range of 0.15 to 0.6 mm and a purity of 99.9% or more. It is preferable that it does not exist and the cubic rate is 90% or more.
Furthermore, in the aluminum foil for electrolytic capacitors according to the present embodiment, the number of crystal grains is 6000 to 15000 / cm ² , and among these, crystal grains having a diameter of 100 μm or less are 50 to 70% in number ratio. In addition, the cubic rate is preferably 90% or more.

In order to manufacture the aluminum foil for electrolytic capacitors according to the present invention, a slab is cast from a molten aluminum or from an alloy melt adjusted to have the above composition ratio, and the slab is soaked at a temperature exceeding 500 ° C. Apply. If necessary, homogenization treatment may be performed prior to soaking.
After the soaking, a hot rolling process is performed. The processing rate at that time is set to 95 to less than 99.0%. If it is less than that, productivity is bad and it is unsuitable industrially. Above that, the finishing temperature is lowered, and the amount of Fe-based precipitates, which are coarse crystal suppression factors, is insufficient. Desirably, it is 95 to 98.5% of range.

In order to obtain a high cubic rate and to suppress the generation of coarse crystal grains, it is necessary to control the amount of Fe-based precipitates, which is a crystal grain growth inhibiting factor.
The amount of precipitate can be obtained by evaluating the Fe concentration of the precipitate collected with a 0.2 μm mesh using a hot phenol extraction method. The amount of Fe-based precipitate is preferably 1 to 4 ppm by mass.
Below this range, it becomes difficult to suppress abnormal growth of crystal grains. Beyond this range, cubic growth is hindered and the cubic rate is reduced.
In hot rolling, when the finishing temperature is less than 250 ° C., the cooling rate near 300 ° C., which is the maximum solid solution region of Fe, is increased during rolling, so the amount of Fe-based precipitates is insufficient. Moreover, when it exceeds 400 degreeC, since a hot rolling structure | tissue will raise | generate recrystallization and the drive force of Fe precipitation will reduce, the amount of Fe type precipitates will run short.
Therefore, the hot rolling finish temperature needs to be 250 to 400 ° C., and the optimum amount of precipitates can be obtained by setting the total amount of Fe to 5 to 20 ppm.
After the hot rolling is finished, cold rolling is performed to obtain a foil thickness of 0.15 to 0.6 mm. If the foil thickness is less than this range, the cubic crystal growth rate during the subsequent annealing is likely to penetrate the foil thickness, so that the growth of the cubic crystals is promoted because the growth of the cubic crystals is stagnated. The rate drops. Even within the above range, a range of 0.2 to 0.4 mm is preferable.

After obtaining a predetermined foil thickness by cold rolling, heat treatment is performed at a temperature of 530 ° C. to 600 ° C. for several hours to grow cubic crystals. In that case, in order to reduce the influence of the oxide film in etching, annealing in an inert gas such as argon, nitrogen gas, or a reducing gas such as hydrogen gas is desirable. In addition, the surface concentration of trace components is performed by this annealing. In particular, elements such as Pb that are strongly concentrated in the surface oxide film have a role of embrittlement of the surface oxide film, and uniform etching cannot be performed unless a certain amount is concentrated. Specifically, in Pb, the ionic strength ratio between the depth position of 0.1 μm and the outermost layer is required to be 2.0 or more. For this purpose, the annealing temperature needs to be 530 ° C. or higher.
Further, when the temperature exceeds 600 ° C., the aluminum foils are in close contact with each other in the coil shape, so that appearance defects such as wrinkles occur. Even if it is the previous range, Preferably it is the range of 550 degreeC-590 degreeC.

The aluminum foil for electrolytic capacitors manufactured as described above has a foil thickness in the range of 0.15 to 0.6 mm, a purity of 99.9 mass% or more, 5 to 20 mass ppm of Fe, and 5 to 50 Si. It is an aluminum foil containing 1 ppm by mass of Cu, 1 to 100 ppm by mass of Cu, 0.1 to 5 ppm by mass of Pb, the balance being Al and inevitable impurities, and there are no coarse crystal grains having a grain size of 5 mm or more, And the cubic rate becomes 90% or more.
Further, the aluminum foil for the electrolytic capacitor, the number of crystal grains is from 6,000 to 15,000 pieces / cm ^2, of these, it is preferable that the following grain diameter 100μm from 50 to 70% in the number ratio.

Here, in this embodiment, 1 m ² of aluminum foil is treated at 30 ° C. (liquid composition: 35% HCl, 60% HNO ₃ , 48% HF mixed at a volume ratio of 33: 33: 1. ) For 30 seconds, washed with water and dried to change the gloss of the (100) -oriented crystal grains and the crystal grains on the other side. A state in which no grains are observed is defined as a state in which no coarse crystal grains are generated.
Further, from this aluminum foil, an area of 30 cm ² is taken in by an image analysis apparatus, and a value obtained by calculating a crystal grain occupancy ratio in the (100) orientation is defined as a cubic crystal ratio.

After the previous rolling process, the aluminum foil for electrolytic capacitors can be finally obtained by subjecting the aluminum foil to a surface roughening treatment and a chemical conversion treatment.
The roughening treatment and chemical conversion treatment performed here may be performed under the general conditions applied to the roughening and chemical conversion treatment of this type of aluminum foil for electrolytic capacitors.

  In the case of an aluminum foil having a foil thickness as described above, no coarse crystal grains, and a cubic crystal ratio of 90% or more, over-dissolution or excessive It is possible to obtain a more uniform etched surface without causing further precipitation.

Fe: 10 mass ppm, Si: 10 mass ppm, Cu 50 mass ppm, Pb 1 mass ppm, other inevitable impurities, and an aluminum alloy having the balance of Al were melted and cast to obtain a plurality of slabs having a thickness of 600 mm. An aluminum plate having various finished thicknesses (3 to 42 mm) was obtained by hot rolling on the slab at various hot rolling rates, and the temperature at the end of hot rolling was measured for each plate. Subsequently, these plate materials were cold-rolled and cold-rolled to a target thickness range of 0.15 mm to 0.6 mm to obtain a plurality of aluminum foil samples. Further, heat treatment was performed at various temperatures in an Ar atmosphere for 6 hours to obtain a target material.
The ion intensity ratio of Pb is measured under the conditions of irradiation ion: O ²⁺ acceleration voltage: 17 kV primary ion current: 200 nA, and the ion intensity at the outermost layer (5 nm) and the ion intensity at the 0.1 μm sputtered position. Compared.

The following table shows the measurement results of the crystal grain ratio and capacity, the bending strength, the cubic crystal ratio, and the number of coarse grains per 100 cm ^{2 of} each sample having a grain size of 100 μm or less.
The capacity evaluation methods shown in the following table show values when electrolysis is carried out for 240 seconds at a current density of 0.1 mA / cm ^{2 in} a solution of 3 mol of sulfuric acid + 1 mol of hydrochloric acid. Moreover, in each Example, the comparison of capacity | capacitance is performed by adjusting electrolysis temperature so that the intensity | strength equivalent to the sample of the comparative example 2 corresponding to a prior art example may be acquired. Therefore, the reason why the capacity of each embodiment is described as being high is that the pits have been grown longer as the aluminum foil is thicker.

The bending strength test shown in Table 2 below is an MIT type automatic bending tester (JIS 8115), in which the bending portion R is set to 1.0 mm, a weight of 2.5 N is applied to a sample having a width of 10 mm, and 90 cycles. Operated at / min. In that case, it counted as 1 time in 1/4 cycle.
In Table 2 below, relative values are shown assuming that the numerical value of Comparative Example 2 is 100.

As is apparent from the results shown in Tables 1 and 2, the samples of the examples having a foil thickness of 0.15 to 0.6 mm and no coarse crystal grains having a diameter of 5 mm or more have a large capacity and are bent. The strength was high, and the cubic rate was also a high value of 90% or more, and in each example sample, the number of crystal grains was in the range of 6000 to 15000 pieces / cm ² .
Moreover, in each Example, the crystal grain ratio with a diameter of 100 micrometers or less was in the range of 50 to 70% by number ratio.
On the other hand, in each sample having a foil thickness of 0.15 to 0.6 mm, the samples of Comparative Examples 1, 7, 8, 11, and 12 in which coarse particles having a diameter of 5 mm or more existed had a reduced capacity. Moreover, the capacity | capacitance fell for the sample of Comparative Examples 3, 4, 5, 6, 9, 10, and 13 with a low cubic rate.

Claims (3)

  Foil thickness is in the range of 0.15 to 0.6 mm, purity is 99.9% by mass or more, Fe is 5 to 20 ppm by mass, Si is 5 to 50 ppm by mass, Cu is 1 to 100 ppm by mass, and Pb is 0.1 It is an aluminum foil containing ˜5 mass ppm, the balance being Al and inevitable impurities, the ionic strength ratio at the depth position of 0.1 μm and the outermost layer in Pb is 2.0 or more, and the particle size is 5 mm. An aluminum foil for electrolytic capacitors, characterized in that the above coarse crystal grains do not exist and the cubic crystal ratio is 90% or more. ^{2. The} aluminum for electrolytic capacitors according to claim 1, wherein the number of crystal grains is 6000 to 15000 pieces / cm ² , and among these, crystal grains having a diameter of 100 μm or less are 50 to 70% in number ratio. Foil. When an aluminum or aluminum alloy ingot is hot rolled and then cold rolled to produce an aluminum foil for an electrolytic capacitor having a thickness of 0.15 to 0.6 mm, the processing rate in the hot rolling is After the temperature at the end of hot rolling is in the range of 250 to 400 ° C. and the foil thickness is in the range of 0.15 to 0.6 mm, the temperature is 530 to 600 ° C. The manufacturing method of the aluminum foil for electrolytic capacitors characterized by performing the heat processing which heats.