JPH0240760B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an etching device for continuously etching aluminum foil for electrolytic capacitors. [Prior Art] Generally, the surface of aluminum foil for electrolytic capacitors is etched in a suitable electrolyte to increase the capacitance. This etching method is broadly divided into medium-high voltage (medium-high voltage) and low-voltage (low voltage) etching methods depending on the use of the electrolytic capacitor. In particular, for low-voltage etched foils in low-voltage electrolytic capacitors, the finer the unevenness formed by etching, the better. This causes the surface roughening rate to decrease. Therefore, there is already an etching device configured to quickly pull up the etching foil from the electrolytic solution after etching, as disclosed in Japanese Patent Publication No. 42-21410 ``Method for Etching Aluminum Foil for Electrolytic Condenser.'' As shown in FIG. 4, this etching apparatus 1
A pair of carbon electrodes 4 and 5 are vertically arranged facing each other in an electrolytic cell 3 filled with a suitable electrolytic solution 2, and power supply rollers 6 and 7 are arranged outside the electrolytic cell 3.
Intermediate rollers 8 and 9 are disposed inside, a power supply 10 is connected between the power supply rollers 6 and 7 and carbon electrodes 4 and 5, and an aluminum foil 11 is introduced from the first power supply roller 6 side. 1 intermediate roller 8 and the second
The power is passed between the carbon electrodes 4 and 5 via an intermediate roller 9, and is led out from the second power supply roller 7 side. Etching of the aluminum foil 11 in this etching apparatus 1 starts from the time when the aluminum foil 11 enters between the lower ends of the carbon electrodes 4 and 5, and progresses while moving toward the upper end, and is pulled up from the electrolytic solution 2. It will end with this. Power sources for etching include AC power, DC power, pulse power, and a combination of these power sources. Further, an insulating plate 12 may be provided on the back, bottom, or side surface of the carbon electrodes 4 and 5 to cut off the current so that no excess current flows. [Problems to be Solved by the Invention] Next, when electrolytically etching aluminum foil, if a constant voltage is applied as shown in FIG.
It is well known that the current changes over time as shown in FIG. This is because the oxide film formed on the surface of the aluminum foil by natural oxidation increases the interfacial resistance at the beginning of etching.
This is because it functions to suppress the flow of current. However, as etching progresses and the oxide film is destroyed, the current increases and converges to a predetermined current. That is, at the start of etching, the current density is lower than the predetermined current density, and this low current density causes the current to concentrate on the aluminum foil, preventing the progress of uniform etching, and eventually causing the rough surface of the etching foil. This is causing a decline in the conversion rate. Therefore, instead of applying a constant voltage, constant current control is generally performed so that a constant current flows. However, when etching is performed using the etching apparatus 1 shown in FIG. 4, the aluminum foil 11 is not etched at the predetermined current density at the etching start point X, which is similar to the case where a constant voltage is applied as described above. A phenomenon is occurring. That is, when a constant current is caused to flow by the constant current control power source 10, the current is constant throughout the carbon electrodes 4 and 5. However, when the aluminum foil 11 is moving from the lower end of the carbon electrodes 4 and 5 to the upper end, it is located near the electrolyte 2 surface Z between the carbon electrodes 4 and 5 and near the middle Y between the carbon electrodes 4 and 5. Etching has progressed sufficiently in the aluminum foil 11, there is almost no oxide film, the interfacial resistance is low, and current flows easily. On the other hand, the aluminum foil 11 located in the vicinity X between the lower ends of the carbon electrodes 4 and 5 has just entered between the carbon electrodes 4 and 5, and has a high interfacial resistance, making it difficult for current to flow. As a result, as shown in FIG. 7, the current density is non-uniform in the length direction of the aluminum foil 11 located between the carbon electrodes 4 and 5. The current density curve shown in FIG. 7 and the current curve shown in FIG. 6 are very similar. As can be seen from this, the etching start point X is significantly lower than the predetermined current density, and the low current density causes current concentration, which prevents uniform etching from progressing. In addition, leakage of etching current (LC) occurs between the lower ends of the carbon electrodes 4 and 5, as shown by the broken line in the figure, and this leakage current (LC) causes a further decrease in current density at that location during etching. It is inviting and undesirable. Therefore, conventionally it has not been possible to obtain an aluminum electrode foil for electrolytic capacitors having the desired high surface roughening ratio. [Means for Solving the Problems] However, the present invention provides an electrolytic capacitor having a high surface roughening rate by increasing the current density at the start of etching to a predetermined value and suppressing current leakage. The purpose of the present invention is to provide an etching device capable of obtaining aluminum foil for use in etching, and specifically, to form protrusions at opposing positions on the lower ends of a pair of opposing carbon electrodes, and to form protrusions for cutting off leakage current. An insulator is provided, and the tips of both insulators are arranged at positions such that the tips do not come into contact with each other and are spaced apart from each other by 0.5 mm to 3.0 mm. [Example] Hereinafter, an etching apparatus 1A according to the present invention will be described.
This will be explained based on FIGS. 3 to 3. Prior to the description, the same parts as in the conventional example shown in FIG. 4 are given the same reference numerals. In the present invention, only particularly improved parts will be explained. As shown in FIG. 1, a pair of carbon electrodes 4,
In order to raise the current density at the start of etching to a predetermined value, opposing protrusions 41 and 51 are formed at the lower end of the etching electrode 5, respectively. These protrusions 41, 5
1 is formed integrally with carbon electrodes 4 and 5 or as a separate structure. The protrusions 41 and 51 can have various shapes, such as a triangular shape as shown in FIG. 1, a rectangular shape as shown in FIG. 2, and a trapezoidal shape as shown in FIG. 3. Distance a between both carbon electrodes 4 and 5 and both protrusions 4
The distance b between 1 and 51 varies depending on the etching conditions, but for example, when etching an aluminum foil 11 with a thickness of 100 μm at a current density of 400 mA/cm ² , the distance a is 50 mm and the distance b is An example is 15mm. Further, as shown in FIG. 1, leakage current blocking insulators 13 and 14 are placed at the lower ends of the pair of carbon electrodes 4 and 5, respectively, in order to prevent current from leaking to areas other than between the carbon electrodes 4 and 5. , the leakage current interrupting insulators 13 and 14 have a positional relationship in which both ends do not touch each other, for example, the distance between the ends c is 1.0 mm.
are arranged so that Electrolytic solution 2 filled in electrolytic cell 3 as insulators 13 and 14 for leakage current interruption
It is preferably made of a material that does not react with other materials, such as a resin material or a rubber material, and has flexibility. Leakage current interrupting insulator 1 arranged in this way
Since the tips of the electrodes 3 and 14 are in contact with each other, the electrolytic solution 2 naturally convects between the carbon electrodes 4 and 5 from the gap between the aluminum foil 11 and the leakage current interrupting insulators 13 and 14, and the carbon electrode 4,5
The circulation of the electrolytic solution 2 between the electrolytic solutions 2 and 2 is improved, and non-uniformity in the temperature of the electrolytic solution 2 in the electrolytic cell 3 and non-uniformity in the Al ³⁺ concentration can be eliminated. In addition, leakage current interrupting insulator 1
3 and 14 and the aluminum foil 11 do not come into contact with each other, so that the aluminum foil 11 is not scratched. Furthermore, if the distance c between the tips is 0.5 to 3.0 mm, current leakage from the lower ends of the carbon electrodes 4 and 5 will not occur during etching of the aluminum foil 11. Next, we will discuss specific etching and its effects. The composition of electrolyte 2 is 0.5M HCl, AlCl ₃
is 0.5M, H ₂ SO ₄ is 0.05M, H ₃ PO ₄ is 0.5M,
An aluminum foil 11 with a purity of 99.99% is etched at a liquid temperature of 60° C. and a current density of 400 mA/cm ² . Next, the etched aluminum foil 11
is chemically formed by applying a voltage of 50 V with an aluminum adibate aqueous solution. Table 1 shows a comparison between the capacitance and bending strength of the chemically formed foil produced in this manner (Example) and the conventional example.

[Table] Example 1 uses carbon electrodes 4 and 5 shown in FIG.
Also, leakage current interrupting insulators 13 and 14 are used. In the reference example, the carbon electrodes 4 and 5 shown in FIG. 3 are used, but the leakage current interrupting insulators 13 and 14 are not used. The conventional example was obtained using the conventional etching apparatus shown in FIG. 4 under the above-mentioned etching conditions and chemical formation conditions. As can be seen from Table 1, the etching foil produced according to the present invention has a larger capacitance and a greater bending strength than the conventional and reference examples. [Effect] As described above, in the present invention, protrusions are formed at opposing positions of the lower ends of each of the pair of opposing carbon electrodes of the etching device, and an insulator for interrupting leakage current is disposed. , it is possible to prevent uneven dissolution of the aluminum foil at the time of starting etching of the aluminum foil as in the prior art. Therefore, it is possible to provide an etching foil having a high surface roughening rate.

[Brief explanation of drawings]

FIG. 1 shows an etching device according to the present invention, FIGS. 2 and 3 show other shapes of carbon electrodes, FIG. 4 shows a conventional etching device, and FIG. 5 shows an applied voltage. FIG. 6 is a diagram showing the current characteristics, and FIG. 7 is a diagram showing the relationship between the current density in the length direction between the aluminum foil and the carbon electrode in the etching apparatus shown in FIG. 4. In the figure, 1, 1A... etching device, 2... electrolyte, 3... electrolytic bath, 4, 5... carbon electrode,
6, 7, 8, 9...roller, 10...power supply, 11
... Aluminum foil, 12 ... Insulating plate, 13,1
4... Leakage current interrupting insulator, 41, 51... Projection.

Claims (1)

[Claims] 1. A pair of carbon electrodes is installed vertically in an electrolytic tank filled with electrolytic solution, and an aluminum box is introduced from the gap between the lower ends of both carbon electrodes to start etching. As the aluminum foil is pulled up from the electrolytic solution, etching begins. In the continuous etching apparatus, protrusions are formed at opposite positions of the lower ends of both carbon electrodes, and the tips of the leakage current interrupting insulators are brought into contact with each other. Tip spacing between each other is 0.5mm~3.0 without
An etching device characterized in that it is arranged in a relationship such that mm.