JPH0266925A - Etching method for electrode foil of aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To manufacture an electrode foil for an aluminum electrolytic capacitor having an area increasing magnification by 20% or more higher than a conventional one and to reduce in size and cost a product by etching the surface of the foil with a positive symmetrical waveform with 5ms or less of rising time of maximum current value of each cycle of an AC current. CONSTITUTION:When the surface of an aluminum foil is etched with an AC current in hydrochloric acid solution containing 3-25% of aluminum chloride at 10-70 deg.C of liquid temperature, it is etched in solution containing acidic acid or ions of one or more types of nitric acid, sulfuric acid, phosphoric acid, oxalic acid as an additive with symmetrical positive and negative waveform having 5ms or less of rising time up to maximum current value of each cycle of an AC current. An etching current at the anode is abruptly raised at 5ms or less to generate an etching pitch uniformly from a defect of a strong film to obtain the foil having an area increasing magnification by approx. 20% higher than that of a conventional one.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of etching electrode foil for aluminum electrolytic capacitors.

Conventional technology A so-called aluminum electrolytic capacitor is constructed by winding aluminum electrode foil and insulating paper and impregnating it with a driving electrolyte. The surface is etched to form irregularities to increase the surface area.

In recent years, with the development of ICs, LSIs, etc., electrolytic capacitors are required to be smaller and thinner, and for this purpose, it is necessary to increase the capacitance per unit area of the electrode foil used. That's why.

Conventionally, the etching method for electrode foil for aluminum electrolytic capacitors has been to use alternating current to take advantage of its strong strength, and patents have also been filed for various additives or waveforms (for example, JP-A No. 58-22390). ).

Problems to be Solved by the Invention However, with a simple conventional waveform (such as a sine wave) and conventional additives, the wavefront multiplier (=capacitance per unit area of electrode foil after etching/capacitance per unit area before etching) The drawback was that the capacitance was insufficient.

The present invention makes it possible to obtain an aluminum electrode foil having a high wavefront magnification.

Means for Solving the Problems In order to solve these conventional problems, the present invention provides a solution of hydrochloric acid containing aluminum chloride at a concentration of 3 to 25.
When etching the surface of an aluminum foil using a current at a solution temperature of 10 to 100°C, nitric acid, sulfuric acid,
It contains one or more oxidizing acids or ions among phosphoric acid and oxalic acid, and etches with a positive and negative symmetrical waveform in which the rise time to the maximum current value of each cycle of alternating current is within e5ms.

Further, the concentration of the additive is 0.01 to 10%.

Effect As mentioned above, it contains an oxidizing acid and the rise time to the maximum current value of each cycle of alternating current is 5! The effect of etching with a waveform within IIS is as follows.

In general, when etching with alternating current in hydrochloric acid, bit generation occurs during the anode (positive) cycle and cand (negative) cycle occurs.
The process progresses through alternating cycles of chemical dissolution and film formation. Therefore, by adding an oxidizing acid, a uniform and strong film is formed at the cathode to suppress chemical dissolution, and by rapidly increasing the etching current at 51115 or less at the anode, the etching is uniformly removed from the defective parts of the strong film. This causes etch bits to occur. In this way, an aluminum foil having a wavefront magnification approximately 20% higher than the conventional one can be obtained.

Embodiment FIG. 1 shows an example of a current waveform according to the present invention, and t indicates the rise time.

FIG. 2 shows the capacitance obtained by etching in a hydrochloric acid solution under the following conditions and then anodizing with an ammonium adipate solution at 70V.

CXffn'fH) 5% HCl + 2% people 7! ce
s [Additive] 1% HNO.

[Aluminum foil 34N, 90μ heavy soft material [Etching temperature] 40°C [Etching time] 5 m process n [Frequency] 20 Hz [Rise time] 1.3, 5, 7.10 m5 2nd
As shown in the figure, the capacitance tends to increase as the rise time becomes faster; it becomes higher than the conventional level at 5 ms or less, and an increase in wavefront magnification of about 20 inches or more at I ms or less. , this effect also has a large interaction with additives, such as nitric acid and sulfuric acid.

It is essential to contain at least one of phosphoric acid and oxalic acid.

Effects of the Invention As described above, according to the etching method of the present invention, it is possible to manufacture electrode foil for aluminum electrolytic capacitors with a higher surface area magnification of 20 inches or more compared to the conventional method, which has a significant effect on product miniaturization and cost reduction. effective.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram showing the etching waveform according to the etching method of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between the rise time and the capacitance, which does not explain the present invention in detail.

Claims (2)

[Claims] (1) When electrolytically etching the surface of aluminum foil using alternating current at a temperature of 10 to 70°C in a hydrochloric acid solution containing aluminum chloride with a concentration of 3 to 25%, nitric acid, sulfuric acid, and phosphoric acid are used as additives. , oxalic acid, or ions, and is etched with a positively symmetrical waveform in which the rise time to the maximum current value of each cycle of alternating current is within 5 ms. Etching method for electrode foil. (2) Claim 1, wherein the concentration of the additive is 0.01 to 10%.
The method of etching electrode foil for an aluminum electrolytic capacitor described above.