JP3983785B2 - Aluminum foil for electrolytic capacitors - Google Patents

Description

  The present invention relates to an aluminum foil for electrolytic capacitors that is roughened by etching and used for electrodes of electrolytic capacitors.

Conventionally, aluminum foil for electrolytic capacitors uses 99.9% or more aluminum purity aluminum foil, and performs AC or DC electrolysis in strong acid to generate fine pits, increase the surface area, and then perform chemical conversion. In addition, a necessary withstand voltage is used (for example, Patent Document 1).
Since the capacitance is proportional to the surface area after etching, it is important to select electrolytic conditions in electrolytic etching. In particular, an etching foil used for low voltage is subjected to electrolysis using an alternating current in order to increase its surface area.
JP 2001-294916 A

However, in the alternating current electrolysis employed in the electrolysis of aluminum foil, a large current is consumed, so that a great deal of cost is required and this is a barrier to cost reduction.
On the other hand, in a part of the foil used for the cathode, the aluminum purity is reduced to about 99%, and a highly chemically soluble foil is used to expand the surface area without electrolysis. This is because the cathode foil does not require a chemical conversion step that causes a problem due to low purity, and thus it is possible to increase chemical solubility using a low-purity aluminum foil as described above.
However, in the etching foil used for the anode foil, when the aluminum purity is lowered and the chemical solubility is increased, in the subsequent chemical conversion process, the amount of impurities in the chemical conversion film increases, resulting in film deterioration such as an increase in leakage current. As a result, the quality is significantly reduced. For this reason, it is necessary to use 99.9% or more aluminum foil in the anode foil in order to avoid the deterioration of the chemical conversion film. As a result, the chemical solubility is low and electroless dissolution is difficult, and etching by the electrolytic method is difficult. It is essential.

  The present invention has been made against the background of the above circumstances, and enhances chemical solubility while maintaining high purity, and thus enables electroless etching and does not cause deterioration of the conversion coating due to low purity. An object is to provide an aluminum foil for a capacitor.

  As a result of intensive studies, the present inventors have found an element that dramatically increases the chemical solubility of the aluminum foil without lowering the aluminum purity, and have completed the present invention.

That is, the invention of the aluminum foil for electrolytic capacitors of the present application is an electrolytic capacitor low-pressure or cathode aluminum foil used for etching, and contains Fe: less than 5 to 50 ppm and Si: 5 to 40 ppm by mass ratio. Further, one or more of Mn, Zn, Ni, Sn, Ag, Pt, and Au are contained in a total of more than 40 to 500 ppm, with the balance being 99.9% or more of Al and inevitable impurities, The amount of Cu in inevitable impurities is controlled to be less than 15 ppm.

  According to the present invention, one or more selected from Mn, Zn, Ni, Sn, Ag, Pt, and Au are included in order to enable generation and growth of etching pits by electroless. These elements and bulk aluminum cause a local cell reaction, which causes pit formation. As a result, high chemical solubility is exhibited. Below, the effect | action of each component and the reason for limitation are demonstrated. In addition, all the following component amounts are mass ratios.

Fe: 5 ppm to less than 50 ppm Fe is an element that generates an intermetallic compound with Al and enhances chemical solubility. However, if the amount is less than the lower limit, the above-described effect cannot be obtained sufficiently. On the other hand, if the amount exceeds the upper limit, the precipitates become large, resulting in defects in the chemical conversion film. Therefore, the Fe content is set to less than 5 to 50 ppm. For the same reason, it is desirable that the lower limit is 20 ppm and the upper limit is 40 ppm.

Si: 5 ppm to 40 ppm
Si, like Fe, generates an intermetallic compound with Al, and is an element that enhances chemical solubility. However, if the amount is less than the lower limit, the above-described effect cannot be obtained sufficiently. On the other hand, if the amount exceeds the upper limit, the precipitates become large, resulting in defects in the chemical conversion film. Therefore, the Si content is set to 5 to 40 ppm. Incidentally, it is desirable to set the lower limit and 20pp m for the same reason.

Cu: less than 15 ppm Cu is also an element that enhances chemical solubility. However, in order to lower the uniform solubility by intensively dissolving the periphery of an intermetallic compound containing Cu, in the present invention, it is not actively added. The content is regulated to less than 15 ppm. Desirably, it is 10 ppm or less.

Mn, Zn, Ni, Sn, Ag, Pt, Au: more than 40 to 500 ppm
Since these elements generate an intermetallic compound with Al to make a potential noble state, a local cell reaction with bulk aluminum can be caused and chemical solubility can be increased. Furthermore, since the compound is on the order of nm, it does not cause a film defect in chemical conversion after etching, so that high quality can be maintained. However, if the total content is 40 ppm or less, the above-described effect cannot be obtained sufficiently and the chemical solubility becomes too low. On the other hand, if it exceeds 500 ppm, a precipitate having a size of μm is generated and becomes a defect of the chemical conversion film. Therefore, the total amount of these elements is determined to be more than 40 to 500 ppm. In addition, these elements should just contain 1 or more types, The combination can be arbitrarily defined between 1 type-7 types, as long as the said total amount is satisfy | filled.
In addition, as for the said total amount, it is desirable for the same reason that a minimum is 50 ppm and an upper limit is 200 ppm.

That is, according to the aluminum foil for electrolytic capacitor of the present invention, there is provided a electrolytic aluminum foil capacitor for low pressure or cathode is subjected to etching, in a weight ratio, Fe: less than 5 to 50 ppm, Si: a. 5 to 40 ppm Further, among Mn, Zn, Ni, Sn, Ag, Pt, Au, one or two or more kinds are contained in a total of more than 40 to 500 ppm, and the balance consists of 99.9% or more of Al and inevitable impurities, Since the amount of Cu in the inevitable impurities is regulated to be less than 15 ppm, chemical solubility is improved, and thus electroless etching is possible. Moreover, since the aluminum purity of 99.9% or more is ensured, deterioration of the chemical conversion film due to low purity is avoided. Therefore, it is possible to produce high quality and low cost etching foil for anode.
It is also possible to subject the aluminum foil of the present invention to electrolytic etching, in which case the roughening rate and reaction rate are improved by high chemical solubility, and electrolysis can be performed at low power. Become.

Hereinafter, an embodiment of the present invention will be described.
Preferably, an aluminum material having a purity of 99.9% or more and prepared to be a component of the present invention can be obtained by a conventional method, and the production method is not particularly limited as the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used. In addition, an aluminum material obtained by continuous casting may 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 foil having a thickness of 50 to 120 μm, for example. In addition, it is also possible to perform one or more intermediate annealings in the middle of cold rolling, and the conditions of this intermediate annealing are not specifically limited as this invention. For example, a treatment in a batch furnace at 200 to 270 ° C. for 1 to 6 hours and a treatment in a continuous furnace at 250 to 300 ° C. for 30 seconds to 10 minutes can be shown. Further, the surface may be cleaned with a chemical during or after cold rolling.
After the cold rolling, final annealing can be performed to obtain a soft foil . Also, aluminum foil of the present invention, after the cold rolled, or may be provided as a rigid foil without performing final annealing.

The aluminum foil obtained through the above steps is then subjected to an etching process.
In general, prior to the etching treatment, chemical pretreatment using an alkali or an acid is performed for the purpose of cleaning the surface. In the present invention, the processing content in the pre-etching process is not limited to a specific one.

The etching step can be performed by electroless etching using an electrolytic solution mainly composed of hydrochloric acid or an electrolytic solution not containing hydrochloric acid. However, the present invention may employ electrolytic etching, and in that case, a good roughening rate can be obtained.
In the etching process, pits are formed with high density even in electroless process, and a high roughening rate is obtained. This foil is subjected to a chemical conversion treatment to obtain a required withstand voltage, and then a capacitor having a high capacitance is obtained by incorporating it as an electrode in an electrolytic capacitor by a conventional method.

While the invention is suitable for use as an anode of the low-pressure electrolytic capacitors, as the present invention be limited to this rather than can also be used as a material for the cathode of the electrolytic capacitor.

Examples of the present invention will be described below.
An aluminum material having the composition shown in Tables 1 and 2 (the amount of each component is ppm, the balance: 99.9% or more Al + inevitable impurities) is melted by a conventional method, and after hot rolling and cold rolling, a thickness of 100 μm An aluminum foil was obtained.
The aluminum foil of the test material shown in Table 1 was subjected to final annealing at 300 ° C. × 4 hr for the hard foil and the aluminum foil shown in Table 2 as a soft foil. The tensile strength was measured for each foil, and the results are shown in Tables 1 and 2.

  Furthermore, after the surface of the aluminum foil was cleaned with a chemical solution, the foil was immersed in a 20% hydrochloric acid, 0.5% sulfuric acid 50 ° C. solution for 600 seconds for electroless etching, and a 15% ammonium adipate solution 85 ° C. Then, formation was performed at a formation voltage of 50 V, and the subsequent capacitance was evaluated. Further, the chemical conversion foil was immersed in a 15% ammonium adipate solution 85 ° C., a constant voltage of 50 V was applied, and the leakage current was measured. The measurement results are shown in Tables 1 and 2.

  As shown in Tables 1 and 2, in Examples including one or more of Mn, Zn, Ni, Sn, Ag, Pt, and Au, a high capacitance was obtained after formation of 50 V, and the surface area was You can see that it has been enlarged. Further, in the case where the above-mentioned necessary elements were not included or were small (Comparative Examples 1 and 2), chemical dissolution did not proceed, and thus the electrostatic capacity was remarkably lowered. Further, when the additive element exceeds the upper limit (Comparative Example 3), a relatively high capacitance can be obtained, but it can be seen that the leakage current increases and the chemical conversion film is deteriorated. Moreover, when there was much Cu, uniform solubility fell and the electrostatic capacitance became low. When Fe and Si were further increased, the capacity was obtained, but the leakage current increased.

Claims (1)

A electrolytic aluminum foil capacitor for low pressure or cathode is subjected to etching, in a weight ratio, Fe: less than 5 to 50 ppm, Si: contain. 5 to 40 ppm, further Mn, Zn, Ni, Sn, Ag, One or two or more of Pt and Au are contained in a total of more than 40 to 500 ppm, with the balance being 99.9% or more of Al and unavoidable impurities, and the amount of Cu in the unavoidable impurities is restricted to less than 15 ppm. An aluminum foil for electrolytic capacitors, characterized in that