JP5182784B2 - Aluminum alloy foil for electrolytic capacitor electrode - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an aluminum alloy foil for electrolytic capacitor electrodes, and more particularly to an aluminum alloy foil suitably used as an anode of a medium / high pressure electrolytic capacitor.

  For the aluminum foil for high-voltage anodes in electrolytic capacitors, DC electrolytic etching is performed to increase the effective area and increase the capacitance per unit area, but this is expanded by the formation of tunnel-like etching pits. Many studies have been conducted on how to effectively increase the effective area.

  For example, in order to control the starting point of the pits on the surface and suppress the entire dissolution of the foil surface and obtain a large area expansion ratio by etching, at least one element of Ti, V, Zr is added. An aluminum foil for electrolytic capacitors that has been added has been proposed in which these elements are concentrated on the surface during final annealing, and the ratio of the concentration of the concentrated surface layer portion to the internal concentration is defined (see Patent Document 1). .

  In addition, in order to obtain a high capacitance by increasing the surface area due to the etching process, it is important to increase the occupancy ratio of the foil (110) plane orientation, and to stabilize the high occupancy ratio of the foil (110) plane orientation. Therefore, in addition to Fe, Si, Cu, and Zn, an aluminum foil for an electrolytic capacitor anode in which the content of Ti, V, Cr, Mn, Zr, Na, Ga, and Mg is defined (patent) Reference 2).

In the proposed aluminum foil for electrolytic capacitors, significant improvement can be obtained in terms of increase in the area expansion ratio and improvement in capacitance due to the etching process. At present, an aluminum alloy foil for an electrolytic capacitor electrode that simultaneously and sufficiently satisfies the conflicting behavior of melting point control as a point has not necessarily been obtained.
JP-A-4-62822 Japanese Patent Laid-Open No. 10-140276

  The present invention was made as a result of further testing and examination of the component composition based on the conventionally proposed aluminum foil in order to eliminate the above-mentioned conventional problems, and its purpose is to contribute to the expansion of the surface area. Electrolytic capacitor electrode that can simultaneously satisfy the contradictory behaviors of suppressing ineffective dissolution of the surface that does not melt and controlling the melting point as the pit start point, and can obtain a high capacitance by increasing the area expansion ratio in the etching process It is to provide an aluminum alloy foil for use.

The aluminum alloy foil for an electrolytic capacitor electrode according to claim 1 for achieving the above object has an aluminum purity of 99.99 % or more, Si: 10 to 25 ppm, Fe: 10 to 19 ppm, Cu: 23 ppm or more and less than 50 ppm, Zn: 5 to 15 ppm, Ga: 5 to 20 ppm, Pb: 0.8 to 1.5 ppm, Cr: 1 to 10 ppm, Zr: 1 to 10 ppm, and the content (ppm) of these elements is as follows: The following relational expressions (1) to (3) are satisfied.
−40 ≦ (Cu-5 × Cr-3 × Zr-15 × Pb) ≦ −10.4 − (1)
Cu ≧ Zn + Ga − (2), 15 ≦ Zn + Ga ≦ 30 − (3)

The aluminum alloy foil for electrolytic capacitor electrodes according to claim 2 has an aluminum purity of 99.99 % or more, Si: 10 to 25 ppm, Fe: 10 to 19 ppm, Cu: 23 ppm to less than 50 ppm, Zn: 5 to 15 ppm, Ga: 5 to 20 ppm, Pb: 0.8 to 1.5 ppm, Cr: 1 to 10 ppm, Zr: 1 to 10 ppm, Mm (Misch metal defined by the total content of La, Ce, Pr, and Nd, and so on. ) Content of 0.1 ppm or less, and the content (ppm) of these elements satisfies the following relational expressions (1) to (3).
−40 ≦ (Cu-5 × Cr-3 × Zr-15 × Pb) ≦ −10.4 − (1)
Cu ≧ Zn + Ga − (2), 15 ≦ Zn + Ga ≦ 30 − (3)

  According to the present invention, it is possible to simultaneously satisfy the contradictory behaviors of the ineffective dissolution suppression of the surface that does not contribute to the surface area expansion and the dissolution point control as the pit start point, and the higher capacitance due to the increase of the surface expansion ratio in the etching process. An aluminum alloy foil for an electrolytic capacitor electrode that makes it possible to obtain the above is provided. In particular, the aluminum alloy foil can be suitably used as an anode for an electrolytic capacitor for medium to high voltage.

The significance and reasons for limitation of the alloy elements in the present invention will be described.
In the present invention, Cu, Cr, Zr, and Pb are selected as elements that contribute to effective surface area expansion by the etching process, and a component range that simultaneously satisfies the surface ineffective dissolution suppression and pit start point increase is defined.

  Factors governing the formation of pits in direct current electrolytic etching are roughly divided into the electrochemical characteristics on the metal side and the amount and distribution of defects in the oxide film formed on the metal surface layer. The present invention has been made as a result of examining the effect on the metal side and the effect on the oxide film, respectively, and confirming the combination capable of expanding the surface area most effectively by their balance.

  First, as a factor on the metal side, when Cu is contained in aluminum having a purity of 99.98% or more and Cu is contained in an amount of 20 ppm or more and less than 50 ppm, the corrosion potential of the material is displaced preciously, and a pitting corrosion reaction is likely to occur during electrolytic etching. It becomes difficult to dissolve. When Cu is 50 ppm or more, a pitting corrosion reaction is likely to occur, and pits are likely to be generated. If Cu is less than 20 ppm, the entire surface is easily dissolved during etching, so that the surface area of the surface region is not efficiently expanded. On the other hand, when the amount of Cu is small, the effect of suppressing the movement of the crystal grain boundaries is reduced during the final annealing, and the crystal grains become coarse. The lower limit of the Cu content is more preferably 23 ppm, the upper limit is 40 ppm, and the more preferable upper limit is 36 ppm. The aluminum purity is more preferably 99.99% or more.

  Similarly, when 1 to 10 ppm of Cr and 1 to 10 ppm of Zr are contained as metal side factors, Cr and Zr are unevenly distributed in the grain boundaries of the rolled structure, and even if the grain boundaries move in the final annealing, Cr and Zr Since the diffusion position has a low diffusion coefficient, it remains at a position along the grain boundary of the original rolled structure. Therefore, during etching, the surface exhibits a fine peeling-like dissolution form, and provides a pit start point on the metal side.

  If Cr and Zr are each less than 1 ppm, the above effects are not sufficient, and the starting point of the etching pit is limited. If it exceeds 10 ppm, peeling-like dissolution occurs frequently, so the surface layer region dissolves more than necessary and is effective. Limited surface area expansion area. The upper limit with more preferable Cr content and Zr content is 6 ppm.

  Since the exfoliation of the surface occurs in a very narrow region, the pit start can be supplied without increasing the ineffective dissolution of the surface layer, but the optimum content of Cr and Zr varies depending on the Cu content, and the Cu content When the corrosion potential changes so much that the pitting corrosion reaction is difficult to occur, the melting point on the metal side can be optimally maintained by increasing the amount of Cr and Zr.

  Even if the above-mentioned factors on the metal side are optimized, it is difficult to control the pit start point because an oxide film having a barrier property formed in the processing process is formed on the surface of the material. Therefore, by concentrating to the surface layer at the time of final annealing and containing 0.8 to 1.5 ppm of Pb which is oxidized in the oxide film or on the outermost surface, moderate defects are formed in the oxide film.

  If the Pb content is less than 0.8 ppm, the amount of defects in the film decreases, so the dispersibility of the pits decreases, which is not preferable. When the content of Pb exceeds 1.5 ppm, the amount of defects in the oxide film becomes excessive and the entire surface is dissolved, and the fine peeling-like dissolution on the metal side surface is excessively affected thereby increasing the ineffective dissolution of the surface. .

  Zn and Ga have a function of lowering the potential, contrary to Cu, and function to maintain the effect of Cu addition. Therefore, it is preferable to restrict Zn to 5 to 15 ppm and Ga to 5 to 20 ppm.

  In order to stably maintain the effect of Cu addition, the relationship (relational expression (2)) of Cu content (ppm), Zn content (ppm), and Ga content (ppm) should be Cu ≧ Zn + Ga. Is desirable. Further, the relationship between Zn content (ppm) and Ga content (ppm) (relational expression (3)) is preferably 15 ≦ Zn + Ga ≦ 30, and more preferably 18 ≦ Zn + Ga ≦ 25.

Since the above-mentioned component elements are offset or promoted individually, it is necessary to contain them in an appropriate balance. As a result of studying the degree of influence of each component element, by satisfying the relational expression (1) given by the following equation, the conflicting behaviors of the ineffective dissolution suppression of the surface that does not contribute to the surface area expansion and the dissolution point control that becomes the pit start point It has been clarified that can be satisfied simultaneously.
−40 ppm ≦ (Cu (ppm) −5 × Cr (ppm) −3 × Zr (ppm) −15 × Pb (ppm)) ≦ −10.4 ppm − (1)

If it is less than −40 ppm, the surface dissolution becomes excessive, the surface area in the vicinity of the surface layer is not efficiently expanded, and the capacitance decreases. Is greater than -10.4ppm is liable to be excessive surface dissolution inhibiting effect of the material, for pit starting point is limited by coalescence like etching pits occur hardly achieve high capacitance due surface area enlargement Become.

  In order to satisfy the above-described effects of the present invention, it is preferable to limit Mm (Misch metal defined by the total amount of La, Ce, Pr, and Nd) present in the material to 0.1 ppm or less. Mm easily combines with Fe present in the material, and forms an Al—Fe—Mm intermetallic compound. The Al—Fe—Mm intermetallic compound acts as a hydrogen reduction point during direct current electrolytic etching, and promotes anodic dissolution that becomes ineffective dissolution on the surface. For this reason, it is preferable to limit Mm to 0.1 ppm or less.

  Fe and Si are present in the aluminum ingot as impurities, but since they are elements that affect the etching property and crystal orientation, it is necessary to control their contents. When Fe is contained in a large amount, an Al—Fe-based precipitate is formed, the dissolution loss during etching is increased, and the generation distribution of etching pits is made uneven. Moreover, when it is less than 10 ppm, it is disadvantageous in terms of purification cost. A more preferable upper limit of the Fe content is 19 ppm.

  Si has an effect of preventing coarsening of crystal grains during recrystallization. When the content range is less than 10 ppm, the effect is small, and when it exceeds 30 ppm, the distribution of etching pits becomes uneven. The more preferable upper limit value of the Si content is 25 ppm, and the most preferable upper limit value is 20 ppm.

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

Example 1 and Comparative Example 1
The aluminum alloy shown in Table 1 is ingoted by DC casting, and the resulting ingot is homogenized according to a conventional method, followed by hot rolling, cold rolling, foil rolling, intermediate annealing, foil rolling, and final annealing. An aluminum foil having a thickness of 0.11 mm was manufactured.

Next, the obtained aluminum foil was subjected to direct current etching treatment at a current density of 0.2 A / cm ^{2 in} an aqueous solution of hydrochloric acid (1 mol) -sulfuric acid (3 mol) (liquid temperature: 75 ° C.). In (1 mol) -phosphoric acid (0.05 mol) (liquid temperature 80 ° C.), direct current etching was performed at a current density of 0.25 A / cm ² to obtain a test material. Dissolution loss was measured. Thereafter, the etched foil (test material) was subjected to a chemical conversion treatment of 400 V, and each capacitance was measured. The measurement results are shown in Table 2.

As shown in Table 2, all of the test materials 1 to 8 according to the present invention have an increase in capacitance as compared with the test materials 12 to 19 that do not satisfy the conditions of the present invention.

Claims (2)

Aluminum purity is 99.99 % or more, Si: 10-25 ppm, Fe: 10-19 ppm, Cu: 23 ppm or more and less than 50 ppm, Zn: 5-15 ppm, Ga: 5-20 ppm, Pb: 0.8-1.5 ppm Cr: 1 to 10 ppm, Zr: 1 to 10 ppm, and the content (ppm) of these elements satisfies the following relational expressions (1) to (3): Aluminum alloy foil.
−40 ≦ (Cu-5 × Cr-3 × Zr-15 × Pb) ≦ −10.4 − (1)
Cu ≧ Zn + Ga − (2), 15 ≦ Zn + Ga ≦ 30 − (3) Aluminum purity is 99.99 % or more, Si: 10-25 ppm, Fe: 10-19 ppm, Cu: 23 ppm or more and less than 50 ppm, Zn: 5-15 ppm, Ga: 5-20 ppm, Pb: 0.8-1.5 ppm Cr: 1 to 10 ppm, Zr: 1 to 10 ppm, Mm (Misch metal defined by the total content of La, Ce, Pr, and Nd, the same shall apply hereinafter) content of 0.1 ppm or less, An aluminum alloy foil for electrolytic capacitor electrodes, wherein the content (ppm) of these elements satisfies the following relational expressions (1) to (3).
−40 ≦ (Cu-5 × Cr-3 × Zr-15 × Pb) ≦ −10.4 − (1)
Cu ≧ Zn + Ga − (2), 15 ≦ Zn + Ga ≦ 30 − (3)