JP5324805B2 - Aluminum foil for high-pressure anodes in electrolytic capacitors - Google Patents

Description

  The present invention relates to an aluminum foil for high-pressure anodes in electrolytic capacitors.

  Aluminum foil used for high-voltage anodes in electrolytic capacitors has high cubic crystal ratio after final annealing, that is, cube orientation (100) plane occupancy, in order to obtain high capacitance, and generates tunnel pits in electrolytic etching processing. It is desirable that it is easy to do.

  In order to obtain an aluminum foil having such characteristics, an aluminum foil added with various component elements, for example, a small amount of Fe, Ni, Co, Cr, Mn, Zr, An aluminum foil in which a specific amount of one or more elements of Ti, V, Mo, Pb, Bi, In, Sn is contained in the oxide film and the content of these elements in the aluminum ground is regulated is proposed. (See Patent Document 1).

In addition, a small amount of a specific element is present in the oxide film, the interface between the oxide film and the aluminum ground, and a specific amount in the aluminum ground, and the etching pits extending in the vertical direction are uniformly aligned to form a capacitance. An improved aluminum foil has also been proposed (see Patent Documents 2 and 3).
JP-A-8-3673 JP 2006-152394 A JP 2006-152402 A

  However, in the above-described conventional aluminum foil, dispersion of etching pits formed by the electrolytic etching process is not always sufficient, and pit coalescence may be partially generated by the diameter expansion etching.

  The present invention has been made as a result of further testing and investigation on the relationship between the combination of a small amount of additive components and the etching characteristics. The purpose of the present invention is to easily generate tunnel pits in the electrolytic etching process and to expand the relationship. An object of the present invention is to provide an aluminum foil for a high-pressure anode in an electrolytic capacitor that has improved pit dispersibility by suppressing pit coalescence in diameter etching and has a high capacitance.

The aluminum foil for high-pressure anodes in electrolytic capacitors according to the present invention for achieving the above object has an aluminum purity of 99.98% (mass%, the same shall apply hereinafter) or more, Si 10-50 ppm, Fe 10-50 ppm, Cu 10-50 ppm, It contains Pb 0.8 to 1.5 ppm, Cr 10 to 100 ppm, the remainder other than the above is inevitable impurities, and the relationship between the Cu content X (ppm) and the Cr content Y (ppm) is 16X + 5Y ≦ 800− ( 1) It is characterized by satisfy | filling Formula.

  According to the present invention, in an electrolytic etching process, tunnel pits are easily generated, and pit coalescence in diameter-enhancing etching is suppressed and improved pit dispersibility is obtained. An aluminum foil for the anode is provided.

  The aluminum foil for high-pressure anodes in electrolytic capacitors according to the present invention is based on aluminum having an aluminum purity of 99.9% or more and containing 10 to 50 ppm of Si and 10 to 50 ppm of Fe. A more preferable aluminum purity is 99.96% or more, and a most preferable aluminum purity is 99.98% or more.

  The significance and reason for limitation of the additive element in the aluminum foil of the present invention will be described. Cu and Cr function to easily generate tunnel pits and improve pit dispersibility in the electrolytic etching process.

  The preferable content of Cu is in the range of 10 to 50 ppm. If it is less than 10 ppm, the effect of suppressing the movement of the crystal grain boundary is reduced during final annealing, and the crystal grains are likely to be coarsened. Pitting corrosion reaction becomes excessive and tunnel pits are hardly generated. The more preferable content range of Cu is 20 to 40 ppm, and the most preferable range is 23 to 36 ppm.

  The preferable content of Cr is in the range of 10 to 100 ppm, and if it is less than 10 ppm, the effect of generating moderately dispersed tunnel pits is not sufficient in the electrolytic etching treatment. The surface area is dissolved more than necessary to limit the effective surface area expansion area. A more preferable content range of Cr is 20 to 60 ppm.

  In the present invention, the combination of Cu and Cr is important. The specific amount of Cu and Cr is allowed to coexist, and the Cu content X (ppm) and the Cr content Y (ppm) are expressed by the formula of 16X + 5Y ≦ 800. By defining it so as to satisfy, moderately dispersed tunnel pits are formed in the electrolytic etching treatment, and the surface expansion ratio is improved and a high capacitance can be achieved.

  Pb acts to improve the formation and dispersibility of pits by causing defects in the oxide film and facilitating dissolution during electrolytic etching. The preferred content is in the range of 0.8 to 1.5 ppm. If the content is less than 0.8 ppm, the amount of defects in the oxide film is small and the dispersibility of pits is small. The amount of defects becomes excessive and the entire surface is melted. Therefore, the micro-peeling dissolution on the surface on the aluminum side is excessive and the ineffective dissolution of the surface is increased.

  The aluminum foil for high-pressure anodes in electrolytic capacitors according to the present invention melts and casts aluminum having a predetermined composition, and the resulting ingot is homogenized by a conventional method, hot rolling, cold rolling, intermediate annealing, Manufactured by final annealing after foil rolling.

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

Examples, comparative examples Aluminum having the composition shown in Table 1 was melted and cast, and the resulting ingot was subjected to homogenization treatment, hot rolling, cold rolling, foil rolling, intermediate annealing, and foil rolling according to a conventional method. After that, the thickness was 0.11 mm, and the final annealing was performed at a temperature of 550 ° C. for 3 hours. In Table 1, those outside the conditions of the present invention are underlined. Moreover, in Table 1, what satisfy | filled (1) Formula was set to (circle), and what does not satisfy (1) Formula was set to x.

Using the obtained aluminum foil as a test material, a current density of 0.2 A / cm ^{2 in} an aqueous solution (liquid temperature 75 ° C.) of hydrochloric acid (1 mol / l) -sulfuric acid (3 mol / l) with respect to the test material. DC etching was performed at a current density of 0.25 A / cm ^{2 in} an aqueous solution of nitric acid (1 mol / l) -phosphoric acid (0.05 mol / l) (liquid temperature 80 ° C.). Went.

  After the etching treatment, the dissolution loss per unit area was measured from the weight difference before and after the etching, and evaluated by a relative value (%) where the dissolution loss of the test material 22 of the comparative example was 100. Thereafter, the etched foil after the above etching treatment was subjected to a chemical conversion treatment at 400 V in a 5% aqueous solution of boric acid to measure the capacitance. ).

  In addition, in order to evaluate the pit dispersibility, the etched foil was subjected to 10-12 μm electrolytic polishing from the surface layer in ethanol perchlorate, followed by SEM observation, and image analysis was performed on the obtained SEM image. The density and average pit diameter were determined. In addition to the single pits, the pit density is obtained by counting the pits (merged pits) that are observed as one pit as a result of merging with each other as one pit. The relative value (%) where the pit density was 100 was evaluated. The average pit diameter (μm) was calculated on the assumption that the pit diameter of each pit (including coalesced pits) was the diameter of a perfect circle having the same area as the pit area of each pit.

  When pits formed under the same etching conditions were subjected to image analysis of a foil with significantly poor pit dispersibility, pit coalescence progressed by diameter expansion etching, so the pit density was counted relatively small, and the average pit diameter Is relatively large due to an increase in coalescence pits. Conversely, a foil having excellent pit dispersibility has a high pit density and a small average pit diameter. From this point of view, the pit dispersibility of the etched foil was evaluated. The pit density was 105% or more and the average pit diameter was 1.15 μm or less, and the pit density was 100% or more and the average pit diameter was 1.20 μm or less. ◯, pit density is 95% or more and average pit diameter is 1.25 μm or less, Δ, pit density is 90% or more and average pit diameter is 1.35 μm or less, ×. Table 2 shows the measurement and evaluation results.

Claims (1)

Aluminum purity is 99.98% by mass or more, Si10-50ppm, Fe10-50ppm, Cu10-50ppm, Pb0.8-1.5ppm, Cr10-100ppm, the rest other than the above are inevitable impurities, Cu A relation between the content X (ppm) and the Cr content Y (ppm) satisfies the following formula (1):
16X + 5Y ≦ 800− (1)