JPS6092489A - Production of aluminum foil for electropolytic capacitor - Google Patents

Abstract

PURPOSE:To produce Al foil having a passive film which is stable and deteriorates less with change in the lapse of time in the stage of producing the Al foil for electrolytic capacity of high-purity Al by treating the Al foil with a specific detergent before or after cold rolling stage for said foil. CONSTITUTION:A secondary electrolytic Al slab having high purity is subjected to hot rolling and cold rolling to form a foil base which is further made into foil having a desired thickness by cold foil rolling and thereafter the foil is subjected to an annealing treatment and electrolytic etching treatment, by which Al foil for an electrolytic capacity is manufactured. The foil base is dipped in a detergent liquid of 5-50wt% concn. of HNO3 before or after the cold foil rolling stage and while an ultrasonic wave is irradiated thereto, the Al foil base is washed to remove thoroughly the rolling mill oil, etc. sticking thereto and at the same time the uniform passive film which is stable and deteriorates less with change in the lapse of time is formed. The Al foil for the electrolytic capacitor having large electrostatic capacity is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing aluminum foil for electrolytic capacitors. In particular, the present invention relates to a method for producing an aluminum foil for electrolytic capacitors that has a stable passive film surface that does not change over time and has excellent water wettability.

Conventionally, aluminum foil for electrolytic capacitors is produced by hot rolling a slab of high-purity secondary electrolytic aluminum to a thickness of about 5 mm, for example, and then cold rolling it to a thickness of about 500 μm+.
(0.5 mm) thick foil base, further cold rolled to the desired thickness, IC, annealed, and then subjected to electrochemical or chemical etching treatment on the foil surface. ing.

Here, the annealing is performed for the purpose of solid solution of impurity elements in aluminum, improvement of the metallographic structure of the foil such as adjustment of crystal orientation, and removal of rolling oil fixed during the rolling process. However, the rolling oil is not completely removed from the aluminum foil manufactured by this method during annealing, and a surface film consisting of aluminum oxide and carbonized rolling oil is formed. Surface dissolution becomes insufficient. As a result, unetched portions in the form of light spots are produced, and there is a problem in which an aluminum foil having a desired capacitance cannot be obtained. Generally, the removal of rolling oil and the formation of aluminum oxide film are
It depends on the J3GJ cooling curve, degree of vacuum, type of rolling oil, adhesion, etc. in the annealing process. The variation tends to be large.

The name of the present invention is based on the results of various studies on optical/1'TJ issues in manufacturing aluminum foil for electrolytic use from secondary electrolytic aluminum slabs of high purity, prior to the annealing process. Before the cold foil rolling process,
The present invention was achieved based on the knowledge that the problem can be solved by cleaning and/or later covering the foil material with a chemical solution. '1J rope J5,
The present invention hot-rolls a slab of secondary electrolytic aluminum,
Next, the foil is cold rolled to obtain a foil base, and the foil is further cold rolled to a desired thickness, and then subjected to annealing treatment and electrolytic etching treatment to produce aluminum foil for electrolytic capacitors. Hit, cold foil rolling ■Before the culm and/
Alternatively, the gist of the present invention is a method for manufacturing an aluminum foil for an electrolytic capacitor, which is characterized in that the foil base is subsequently treated with a cleaning agent containing nitric acid as a main component.

The present invention will be described in detail below. In the production of aluminum foil for electrolytic capacitors, cleaning agents such as hydrofluoric acid, caustic soda, and silicic acid are effective for completely removing rolling oil adhering to the surface of the foil. It has been known for a long time. However, these materials are highly etching (corrosive) and will dissolve the aluminum base as it is. As a result, the active surface is exposed, and a non-uniform oxide film having a thickness of several tens to several hundreds of angles is formed by reacting with oxygen in the air on the foil surface. At the same time, the aluminum dissolved in the cleaning agent forms a hydroxide layer and C is deposited unevenly on the surface, which cannot be sufficiently removed even by subsequent surface treatments. Therefore, a foil substrate with such a non-uniform surface is not suitable for etching after annealing, and a large capacitance cannot be removed even when used as an electrolytic capacitor.

On the other hand, organic acids such as sulfamic acid and surfactants used in cleaning agents with weak or non-jetting properties do not sufficiently remove the rolling oil that has settled on the foil surface, making it impossible to achieve the purpose of cleaning. .

In contrast to these conventional cleaning agents, the present invention is characterized in that a cleaning treatment using a cleaning agent containing nitric acid as a main component is carried out during and/or after the cold foil rolling process. A cleaning agent containing nitric acid as its main component sufficiently removes the rolling oil that sticks to the surface of the foil substrate, and has a mild tweezing effect on the aluminum substrate, slowing down the natural oxidation film caused by the reaction of M elements in the air. It has been found by the inventors to be suitable as a cleaning agent. In other words, a cleaning agent containing nitric acid as a main component easily decomposes and removes the rolling oil adhering to the surface of the aluminum foil, and forms a uniform passive film that is stable and does not change over time, so it can be used for the next annealing process. The thickness of the oxide film produced in this case is thin.

Therefore, it is possible to obtain an aluminum foil for use in electrolytic capacitors which has a sufficient capacitance while increasing the etching effect and improving water wettability.

The concentration of nitric acid in the cleaning agent is 5 to 50% by weight, preferably 10 to 30% by weight; if it is lower than 5% by weight, the sufficient effect cannot be exerted, and the concentration is higher than 50,000m%J. This increases the burden of waste liquid treatment.

A cleaning agent containing Ia acid as a main component may contain mineral acids such as phosphoric acid, nitrates, nitrites, and cleaning aids such as surfactants, if necessary.

The blending ratio of the auxiliary agent should be determined depending on the degree of adhesion of rolling oil, and if the amount of adhesion is large, increase the amount of the auxiliary agent. In the case of mineral acid, it is 1/10 to 1/2 ffiff compared to nitric acid.
i%, (1/1000 to 1/10 in case of other auxiliaries)
% weight is effective.

In the cleaning treatment, a slab of high-purity secondary electrolytic aluminum is hot-rolled in a bath containing a cleaning agent mainly composed of nitric acid heated to 20-95°C, preferably 40-70°C, and then cooled. The thickness before cold rolling, which has been rolled by 1q, is about 50
Either 0μII (0,511111) aluminum foil material is continuously introduced, or a 7norminium foil material before annealing that has been cold-rolled and then cold-rolled to the desired thickness is continuously introduced. Alternatively, the foil may be soaked for 2 to 300 seconds before and after cold rolling. When this cleaning is performed under ultrasonic irradiation, the cleaning efficiency is increased by 1q, and the processing time is reduced by 50% or more. The reason for this is thought to be that the ultrasonic wave causes the fine A+I+ generated by the air bubbles to float, making it easier for the cleaning agent to penetrate.

The aluminum foil that has been cleaned as described above can be cleaned using a known method, for example, at 250 to 600°C in a vacuum and in an oxygen-free atmosphere.
, held for 2 to 10 hours for annealing treatment. Thereafter, the surface is roughened by alternating current or direct current electrolytic nipping by a known method.
A current of 2 to 550 V is passed through an aqueous ammonium acid solution to chemically form the surface of the aluminum foil, forming a desired aluminum foil for an electrolytic capacitor.

As described above, the present invention provides a method for manufacturing aluminum foil for electrolytic capacitors by rolling a slab of high-purity secondary electrolytic aluminum, before and/or after the cold foil rolling process.
Alternatively, the foil material is then treated with a cleaning agent containing nitric acid as its main component, which dissolves the rolling oil adhering to the surface and forms a uniform, stable, passive film that does not change over time. An aluminum foil suitable for use in electrolysis, which has a water wettability of 4a and has a large capacitance by electrolytic etching, can be produced by electrolytic etching.

Next, the present invention will be described with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

In an example, a slab of electrolytic aluminum was hot-rolled, then cold-rolled to obtain a foil base, and a 99.99% pure aluminum foil with a thickness of 100μ sheath obtained by cold-rolling was further treated with nitric acid. The treated aluminum foil was placed in a cleaning bath containing the main ingredient and washed under the treatment conditions shown in Table 1, and the treated aluminum foil was examined for water wettability and corrosion resistance +IU by visual observation. The results of b are shown in Table 1. A comparative example is about the same aluminum foil.

Clean the sample using a conventional cleaning agent and record the IC results.

Table 1 Note 1 Corrosion resistance is 1-ICC vertical weight% heated to 40℃
Aluminum foil was immersed in the water, and the time required for bubbles to appear was measured.

Note 2 Water wettability was measured as follows.

In pure water? The degree of water repellency when immersed in r'+@ and pulled out was observed, and those with no repellency were designated as 01. Those with repellence at the end were designated as Δ.

Next, the aluminum foils obtained in the above Examples and Comparative Examples were heated at a temperature of 260'CI'' under a vacuum of 10 Torr.
After 10 hours annealing, 200mA10 in 4% HC
AC electrolytic etching was performed at 80° C. for 2 minutes. The resulting etched aluminum foil was subjected to a chemical conversion treatment at 22 V in an aqueous ammonium borate solution, and its specific capacitance (C1) was measured. At the same time, the absence of light spots was examined by visual observation. The results are shown in Table 2.

The specific capacitance is measured as follows: 1=o=15
The sample was immersed in a 3% ammonium borate aqueous solution, and a Δg plate with an area approximately 100 times that of the sample was used as the counter electrode.
It was measured using an LCR meter 4262A manufactured by IP, and the parallel capacitance was taken into account, and the capacitance 1H for the example was taken as the specific capacitance.

Table 2 Table 3 Table 4 As can be seen from the above results, aluminum foil treated with a cleaning agent containing nitric acid as a main component according to the method of the present invention has a lower water content than when treated with a known cleaning agent. Excellent wettability, f#4 corrosion resistance, and stable immobility on the surface M
It is clear that 'A' is formed. Therefore, the etching process after annealing progresses evenly and sufficiently.
, no spot heat phenomenon was observed on the surface, specific capacitance t):]
It is clear that there is something satisfactory for capacitors.

Example 2 The ammonium foil of Example and Comparative Example, which had been cleaned and treated according to the treatment procedure shown in Table 1 above, was annealed for 6 hours at 1i+0570''C under a vacuum of 10''3 Torr. Electrocurrent [:S-Tubung] was performed in 4% lIC1 at 200 Δ/aa for 2 minutes at 80°C. (The etched aluminum foil was subjected to chemical conversion treatment at 375V in an aqueous ammonium borate solution, and the capacitance was measured.
4) After t, the presence or absence of light spots was investigated by visual inspection of vQ. The results are shown in Table 3.

As can be seen from the above results, by the method of the present invention, aluminum foil treated with a cleaning agent containing nitric acid as a main component can be treated with aluminum foil treated with a known cleaning agent, regardless of the annealing conditions. It is clear that the etching process after annealing progressed uniformly compared to the standard, no light spot phenomenon was observed on the surface, and the specific capacitance was satisfactory for use as a fundenzer.

Example 3 A 99.99% pure aluminum foil with a thickness of 100 μm, which was the same as that used in Example 1, was introduced into a cleaning bath consisting of IO% nitric acid maintained at a humidity of 65° C., and was washed for the times shown in Table 4. , and the water wettability of each of the treated aluminum foils obtained by washing with ultrasonic irradiation Q.1 was investigated by external appearance observation. Further, each treated aluminum foil was subjected to annealing, immediate AC electrolytic etching, and chemical conversion treatment under the same conditions as in Example 1, and the specific static capacity 7G rlB was measured. The results are shown in Table 4.

From the results in Table 4, it is clear that if the cleaning method using ultrasonic irradiation is applied during the cleaning process, the cleaning effect will be even more effective, and the aluminum foil produced by 1q will be compared to that cleaned without applying ultrasonic irradiation. It also has high capacitance.

Example 4 A slab of secondary electrolytic aluminum was hot-rolled and then cold-rolled to give '+*t,:J'7 490μ... (0,,
A 99% aluminum strip coil foil with a purity of 95) and 19 mm) was introduced into a cleaning bath consisting of 40% nitric acid maintained at a humidity of 65° C., and was immersed for 3 minutes to be cleaned.

Next, this was rolled into a foil using a cold rolling machine to a thickness of 100 μm.
<0.1++++++++) After IC was made into J-thick aluminum 3, it was annealed and AC electrolyzed under the same conditions as Example 1.
Nzingu, Oh J, Bi Kasei Dojo J! I! When L/'U and its capacitance ffz were measured, it was 22.3 μF/-. On the other hand, for comparison, a sample obtained by cold rolling, annealing, alternating current electrolysis, and chemical conversion treatment under the same conditions as the present example was not subjected to cleaning treatment with /IO% nitric acid. The capacitance of aluminum foil is 20°1μ
/aδ, the capacitance of the nine examples of the present invention showed a larger value.

Claims (1)

[Claims] 1 A slab of secondary electrolytic aluminum is hot-rolled, then cold-rolled to form a foil base, and further cold-rolled to form a foil of a desired thickness, In producing aluminum foil for electrolytic capacitors by annealing and electrolytic etching, cold rolling of the foil - [before the culm J3 and /
Alternatively, a method for producing an aluminum foil for electrolysis is characterized in that the foil base is subsequently treated with a cleaning agent that covers nitric acid with the 31-component. 2 S! of the aluminum foil for electrolytic capacitors according to claim 1, wherein the l, rl acid depth in the cleaning agent is 5 to 50 and 96 by weight. I-building method. 3 Applying ultrasonic irradiation in cleaning treatment with cleaning agent 1'! r, yrProduction method of aluminum foil for electrolytic capacitors according to claim 1 or 2