JPH03142912A - Etching process of aluminum foil for electrolytic condenser - Google Patents

Abstract

PURPOSE:To obtain a high diffusion surface magnification by a method wherein natural oxide film on the surface of an aluminum foil is removed down to the low level capable of neglecting the resistance thereof by performing a preliminary chemical etching process. CONSTITUTION:Before starting the etching process of an aluminum foil, a vessel 1 for chemical etching process containing water solution mainly comprising hydrochloric acid as well as an electrolysis vessel 2 for electric etching process are prepared, firstly an aluminum foil A is preliminarily chemically etched in the vessel 1 and then immersed in the electrolysis vessel 2 to perform the electrical etching process. At this time, if phosphoric acid, sulfuric acid, nitric acid, oxalic acid, etc., working as a film forming agent are added to the chemical etchant, bits in more even and higher density can be formed. Furthermore, natural oxide film on the surface of aluminum foil can be removed down to the low level capable of neglecting the resistance thereof by performing said preliminary chemical etching process. Thus, the sufficient diffusion surface magnification can be obtained.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of etching aluminum foil for electrolytic capacitors, and more specifically, to a method of etching electrode foil for low-voltage aluminum electrolytic capacitors. [Prior Art] In general, low-voltage electrode foils are etched using an alternating current etching method in which an alternating current is passed in an aqueous solution containing chlorine ions. Industrially, a continuous etching method is used in which an electrode is placed in an etching tank and an aluminum foil is moved into the tank at a constant speed. In this case, the ideal current distribution in the etching tank is such that the current suddenly rises almost at the same time as the aluminum foil enters the tank, and then a current with a constant current density flows immediately. In other words, if the current suddenly rises at the same time as etching starts, the chlorine ions are sufficiently accelerated by the electric field and attack the aluminum foil surface.
This is because a large number of fine corrosion starting points (bits) are formed and a high surface magnification can be obtained. On the other hand, if the rise of the current is delayed, corrosion initiation points are formed before the chlorine ions are sufficiently accelerated, resulting in fewer corrosion holes with a smaller number of relatively large diameters. As a result, sufficient wavefront magnification cannot be obtained. [Problem to be solved by the invention] However, in the actual manufacturing process using the continuous etching method, when the aluminum foil plunges into the liquid surface of the electrolyte, the resistance of the natural oxide film existing on the surface of the aluminum foil causes the current to drop. The sudden rise is inhibited, and the current distribution actually becomes such that the current gradually increases. Therefore, there was a problem in that the number of corrosion initiation points decreased and a sufficient wavefront magnification could not be obtained. [Means for Solving the Problems] In order to solve the above problems, in the present invention, the aluminum foil is etched by applying an alternating current while continuously immersing the aluminum foil in an electrolytic solution at a predetermined speed. Prior to this, the aluminum foil is preliminarily chemically etched in an aqueous solution containing mainly hydrochloric acid for a predetermined period of time. To explain specifically with reference to FIG. 1, an Mll for chemical etching containing an aqueous solution containing mainly hydrochloric acid and an electrolytic bath 2 for electric etching are prepared. Preliminary chemical etching at
Next, main etching is performed electrically by immersion in an electrolytic bath 2. In this case, adding phosphoric acid, sulfuric acid, nitric acid, oxalic acid, etc., which have a film-forming effect to the chemical etching solution described above, will result in a more uniform and dense etching. A pit is formed. As for the chemical etching time in tank 1. The time is preferably 30 seconds to 10 minutes, preferably 2 to 7 minutes. 30
If it takes less than a second, the progress of chemical etching is insufficient, while if it takes more than 10 minutes, it is unsatisfactory in terms of productivity. Further, the temperature is in the range of 10 to 90°C, preferably 20 to 70°C. If the temperature is 10° C. or lower, chemical etching takes too much time, whereas if the temperature is 90° C. or higher, chemical etching is too fast and may result in non-uniform etching. In the electrolytic bath 2 in which main etching is performed electrically, three electrode plates 28 to 2c are arranged between them with an aluminum ff
Two alternating current types 14a and 4b are provided which are arranged to sandwich 1A and are in a synchronous relationship. In FIG. 1, one AC power source 4a is connected between the middle electrode plate 2b and the left electrode plate 2a, and the middle electrode plate 2b and the right electrode plate 2a are connected to each other.
The other AC power source 4b is connected between the AC power source 4b and the AC power source 4b. Note that one etching process may be replaced by multi-stage etching such as two-stage etching or three-stage etching. [Operation] This preliminary chemical etching removes the natural oxide film on the surface of the aluminum foil to the extent that its resistance can be ignored. (Example 1) First, an aluminum foil was immersed in an etching solution (solution temperature: 40° C.) containing 9 vt% HCI for 2 minutes to perform preliminary chemical etching. Next, as the main etching, 11C
:17wt%jlc131wt%, ll3PO, 1wt
%, in an etching solution with a liquid temperature of 30°C, a current density of 4
Electrical etching was performed by applying an alternating current of 00 mA/aJ and a frequency of 30) Iz for 6 minutes. (Example 2) Preliminary chemical etching was performed under the same conditions as in Example 1. After that, IIcI 7wt%, AlCl,
ltt%. 11. Using an etching solution containing 1 wt% of Po4 and 0.1 wt% of IIN, the main etching was carried out in three stages as follows. [-th row] Set the liquid temperature to 30℃, and check the current! ! y degree 400mA
/d, and an alternating current with a frequency of 3011z was applied for 2 minutes. [Second stage] Liquid temperature is 25℃, current is 15℃ 300++
A/a&, an alternating current with a frequency of 2511z was applied for 3 minutes. [Third stage] Liquid temperature is 20℃, current density is 200mA/a
1, and an alternating current with a frequency of 2011z was applied for 3 minutes. (Example 3) Aluminum foil was first coated with )ICI 7wt%, H, P
Preliminary chemical etching was performed by immersing it in a pre-etching solution containing 1 vt% O4 and a liquid temperature of 30° C. for 3 minutes. Next, main etching was performed under the same conditions as in Example 1, that is, IC:l
7vt%, AlCl, 1wt%, )13PO41w
Main electrical etching was performed by applying an alternating current with a current density of 400 mA/aJ and a frequency of 30 cells for 6 minutes in an etching solution with a temperature of 30° C. and a concentration of 400 mA/aJ. (Example 4) Preliminary chemical etching was performed under the same conditions as Example 3.
Next, one-line etching was performed in three stages under the same conditions as in Example 2. [Comparative Example 1] Aluminum foil was exposed to II without pre-etching.
cI 7wt%, AlCl, 1wt%, It, PO,
In an etching solution with lvt% and a liquid temperature of 30°C, the current density was 400 A/d. Electrical etching was performed by applying an alternating current with a frequency of 30 for 6 minutes. [Comparative Example 2] )1cI 7wt%, AlCl, 1wt%, )13P
O, lvt%, llN0. Using an etching solution of 1@It%, main etching was carried out in three stages as follows without pre-etching. [-th stage] Liquid temperature is 30℃, current density is 400A/a
I. An alternating current with a frequency of 30 cells was applied for 2 minutes. [Second stage] Liquid temperature is 25℃, current density is 300mA/a
J, an alternating current with a frequency of 25#h was applied for 3 minutes. [Third stage] Liquid temperature is 20℃, current density is 200mA/a
J, an alternating current with a frequency of 2011z was applied for 3 minutes. Regarding each aluminum foil etched in the above Examples and Comparative Examples, its 50V power capacity (μF
/cd) and the durability of the bending test are shown below.

【table】

From this table, it can be seen that by performing preliminary chemical etching prior to etching, an aluminum etched foil having excellent capacitance and mechanical strength can be obtained. In particular, it can be seen that even if the main etching is multi-stage etching as in Examples 2 and 4, the preliminary etching is sufficiently effective. [Effects of the Invention] As explained above, according to the present invention, prior to the main etching, preliminary chemical etching is performed to remove the natural oxide film on the surface of the aluminum foil to the extent that its resistance can be ignored. As a result, many fine corrosion initiation points (pits) are formed during the main etching, and a high wavefront magnification can be obtained. Furthermore, an aluminum foil for electrolytic capacitors which is excellent also in terms of mechanical strength can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram schematically showing an example of an etching apparatus used for carrying out the present invention. In the figure, 1 is a chemical etching tank, and 2 is an electrolytic tank.

Claims (2)

[Claims] (1) In an etching method for aluminum foil for electrolytic capacitors, the aluminum foil is etched by applying an alternating current while continuously immersing the aluminum foil in an electrolytic solution at a predetermined speed, as a pre-step to the etching described above. A method for etching aluminum foil for electrolytic capacitors, which comprises preliminary chemical etching of aluminum foil for a predetermined period of time in an aqueous solution containing mainly hydrochloric acid. (2) The method for etching aluminum foil for an electrolytic capacitor according to claim 1, wherein at least one of phosphoric acid, oxalic acid, sulfuric acid, and nitric acid is mixed as an additive into the etching solution for the chemical etching.