JPS5834926B2 - Manufacturing method of aluminum foil for electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing aluminum foil for electrolytic capacitors.

Aluminum foil for electrolytic capacitors must have a large capacitance per unit area.

In order to increase the capacitance, it is sufficient to increase the surface area of the aluminum surface, and for this purpose, the surface of the aluminum foil is subjected to electrochemical or chemical etching treatment.

In order to improve this etching performance, conventionally, before etching treatment, etching is performed at 5000C to 600C in an inert gas atmosphere such as argon or in a non-oxidizing atmosphere such as vacuum.
Although aluminum foils are subjected to high-temperature heat treatment for 2 to 10 hours, there is still a problem that satisfactory etching performance cannot be obtained and, furthermore, sufficient capacitance cannot be obtained.

Therefore, in order to obtain an aluminum foil for electrolytic capacitors with excellent etching performance, the applicant previously conducted a process of forming a water treatment film on the surface of the aluminum foil before electrochemical or chemical etching treatment. γ-A120 was obtained by heating the aluminum foil with the hydration treatment film at high temperature in a non-oxidizing atmosphere to crystallize the water treatment film.
proposed a manufacturing method characterized by passing through a step of changing into three films (Japanese Patent Application Laid-open No. 16857/1983).

The γ-A1203 film on the surface obtained by this method is a fine crystallized film, so when the surface of this aluminum foil is etched, the grain boundaries of the γ-A1203 film take priority in the form of pitting corrosion. It has been found that due to the micro-etching and the miniaturization of the crystals, a highly dense etched state results, which greatly increases the surface area and, as a result, significantly increases the capacitance.

However, in actual production, the high-temperature heat treatment of aluminum foil in a non-oxidizing atmosphere is performed while the foil is wound into a coil. The temperature distribution is different between the two, and a difference naturally occurs in the heating temperature.As a result, the film on the surface of the aluminum foil on the inside becomes insufficiently crystallized, and the etching performance deteriorates compared to the aluminum base on the outside. A problem occurs.

In order to sufficiently promote the crystallization of the aluminum foil on the one side, if the heating temperature is raised, the crystallization of the aluminum foil on the outer side will be excessive, resulting in a film that becomes too thick, which will adversely affect the etching performance. be.

In any case, there was a problem in that the capacitance in the length direction of the coil varied.

In view of the above points, this invention is an improvement on the previously proposed invention, and the feature of the method for manufacturing aluminum foil for electrolytic capacitors is that before electrochemical or chemical etching treatment, This process involves forming a rough surface that communicates in the width direction on the surface of the aluminum foil, forming a water-use treatment film on the surface of the roughened aluminum foil, and forming a coiled aluminum coated with the water-use treatment film. The method is characterized by a step of heating the foil at a high temperature in a non-oxidizing atmosphere to change the water utilization treatment film into a crystallized γ-A1203 film.

The aluminum foil preferably has a high purity of 99.99%, but is not limited to this, and may have a purity within the range used for electrolytic capacitors.

As a specific example of roughening the surface of aluminum foil, 2
Examples include a polymerization rolling method in which sheets of aluminum foil are piled up and rolled, an embossing roll rolling method in which an embossing roll with a grid pattern or the like is used, and a method in which the surface is brushed.

In short, it is sufficient to obtain a rough surface that communicates in the width direction of the aluminum foil.

Specific examples of methods for forming a water treatment film on the surface of aluminum foil include a method of spraying steam or moist air onto the surface of the aluminum foil, a method of heat treatment at a low temperature of about 200°C in the atmosphere, and a method of heat treatment at a low temperature of about 200°C in the atmosphere. Examples include a so-called boehmite treatment method in which aluminum foil is immersed in water or an aqueous amine solution.

By subjecting the aluminum foil on which the water-use treatment film has been formed in this way to a high-temperature heat treatment in a non-oxidizing atmosphere, the water-use treatment film is transformed into a crystallized γ-A1203 film. Crystallized γ-A1
The reason why the aluminum foil having the No. 203 film has excellent etching performance when subjected to etching treatment is as described above.

By forming a rough surface that communicates in the width direction on the surface of the aluminum foil, the temperature distribution between the inside and outside of the aluminum foil coil during high-temperature heat treatment becomes uniform. A fluid passage is created between the aluminum foil layers, and convection occurs in the heated atmosphere in the furnace from this fluid passage, making the temperature of the inner aluminum foil and the outer aluminum foil uniform.

As a result, the crystallization state of the coatings on the inside and outside of the coil becomes uniform, eliminating the conventional problem of variations in capacitance in the length direction of the coil.

The thickness of the crystallized γ-A1203 film is preferably in the range of 40 to 200.
The thickness of the 203 film is about 80λ.

In this invention, the aluminum foil was heated to a high temperature in a non-oxidizing atmosphere in order to prevent the crystallized γ-A1203 film from becoming too thick.

If the film is too thick, etching cannot be performed sufficiently and the etching becomes non-uniform, resulting in a significant decrease in capacitance.A thick film also causes the surface to become cloudy, reducing its commercial value.

Note that the temperature and time in the above-mentioned high-temperature heat treatment are not particularly different from those in the conventional case.

Next, embodiments of this invention will be described.

Example 1 Before electrochemical or chemical etching treatment, a strip-shaped aluminum foil with a purity of 99.99% and a thickness of 100 μm is first polymerized and rolled to form a rough surface communicating in the width direction on its surface.

The surface roughness was 2.4μ parallel to the rolling direction and 1μ perpendicular to the rolling direction.

Next, this roughened aluminum foil is wound into a coil and heated in the atmosphere at 200° C. for 6 hours to form a water conservation treatment film on its surface.

Finally, this aluminum foil was heated at 550° C. for 4 hours in an argon gas atmosphere to transform the water treatment film into a crystallized γ-A1203 film.

Example 2 In water utilization treatment, instead of heating in the atmosphere, steam at about 100'C was applied to the aluminum surface at a flow rate of 7 liters using a nozzle.
A film of crystallized γ-A1203 was obtained on the surface of the aluminum foil in the same manner as in Example 1, except that the spraying was performed at a rate of /min.

Example 3 The aluminum foil surface was roughened in the same manner as in Example 1, except that instead of polymerization rolling, a roughened surface with a roughness of 3μ and communicating in the width direction was obtained on the surface by emboss roll rolling. A crystallized γ-A1203 film was obtained.

Comparative Example A crystallized γ-A1203 film was obtained on the surface of an aluminum foil in the same manner as in Example 1, except that the surface roughening was omitted.

Conventional Example The same aluminum foil as in Example 1 was wound into a coil and heated at 550° C. for 4 hours in an argon gas atmosphere.

The results of measuring the capacitance after etching each aluminum foil obtained in the above example are shown in the table below.

The capacitance measurement results are based on the aluminum foil after treatment at a current density of 10/dm in a 3% aqueous hydrochloric acid solution (85°C).
', perform electrolytic etching treatment for 5 minutes, and then
% boric acid aqueous solution at a chemical conversion voltage of 350V.

As described above, according to the present invention, there is almost no variation in capacitance between the inside and outside of the coil, and the capacitance after etching is significantly increased compared to conventional products.

In addition, when a method of heating in the atmosphere is used as in Example 1 and Example 3 as the process of forming the water use treatment film, the water use treatment film is formed in the recesses obtained by the surface roughening process. This also results in the retention of moisture, which contributes to the promotion of the formation of a crystallized film.

Furthermore, since the surface is roughened in advance, the surface area during etching is increased, and it is also expected that the capacitance will be further improved.

Claims (1)

[Claims] 1. Before electrochemical or chemical etching treatment, a step of forming a rough surface communicating in the width direction on the surface of the aluminum foil, and a step of forming a water conservation treatment film on the roughened surface of the aluminum foil. , an aluminum foil for electrolytic capacitors, characterized in that the coiled aluminum foil on which the water use treatment film is formed is heated at high temperature in a non-oxidizing atmosphere to change the water use treatment film into a crystallized γ-A1203 film. Production method.