JPS63143242A - Production of aluminum foil for electrolytic condenser - Google Patents

Abstract

PURPOSE:To prevent the generation of edge cracks and to uniformly form a thin oxidation film by performing continuous casting by using a mold having an outlet which is heated above the solidification temp. of Al and subjecting Al ingots with impure elements uniformly distributed to rolling processing. CONSTITUTION:The outlet part of a molten metal 6 of the mold 2 is heated up to >=600 deg.C at the solidification point of Al. The Al ingots 3 are continuously cast by using said mold 2. A solid interface 5 is then penetrated into the molten metal 6 of the mold 2 and the impure elements are uniformly distributed to obtain the ingots 3 without crystal grain solidifying boundaries. The ingots 3 are then subjected to the rolling processing and Al foil is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing aluminum foil for electrolytic capacitors, in which the foil is obtained by rolling an aluminum ingot.

[Conventional technology]

As aluminum foil for electrolytic capacitors, conventional 99.
Aluminum ingots made of polycrystalline material with a high purity of 99% or more are processed into foils, which are generally used.

[Problem that the invention seeks to solve]

Aluminum foil for electrolytic capacitors is used as an anode of a capacitor after a highly insulating and high dielectric constant oxide film is formed on the surface of the foil by anodic oxidation or chemical conversion treatment. With the recent miniaturization of electronic devices, there is a strong demand for smaller electrolytic capacitors used as components. In order to miniaturize electrolytic capacitors, it is necessary that the aluminum foil used and the oxide film formed on its surface be thin. In order to manufacture thin aluminum foil, it is necessary that the original raw material, the ingot, is free from segregation of impurity elements as well as foreign solid particles. Although foreign solid particles can be removed by filtering, impurity elements such as iron and silicon dissolved in the molten aluminum as solutes segregate at the grain boundaries of the crystals when the molten aluminum solidifies. When such an ingot is rolled, holes and cracks are generated in the foil due to the segregation of impurity elements existing at the solidification grain boundaries. Furthermore, the formation of an oxide film during anodic oxidation or chemical conversion treatment on the surface of the aluminum foil becomes uneven. Local defects in the oxide film layer on the aluminum foil surface due to the segregation of iron and silicon at grain boundaries significantly reduce the insulation properties of the oxide film. In order to reduce the amount, a special method has been adopted in which aluminum is subjected to three-layer electrolytic scouring to achieve a purity of over 99.99%. Furthermore, in order to produce high-grade capacitor foil, a method has been adopted in which impurity elements are removed from the obtained 7/L/minium ingot using a zone melting refining method, and then the foil is rolled. . All of these involve complicated processes and consume a large amount of energy and time.

An object of the present invention is to provide a method for producing aluminum foil for electrolytic capacitors, which can form a uniform oxide film using industrially pure aluminum as a raw material.

[Means for Solving the Problems] and [Effects of the Invention] The present invention is a method for producing aluminum foil for electrolytic capacitors, in which the foil is obtained by rolling an aluminum ingot, and is characterized by the following: shall be. That is, since the ingot is continuously cast using a mold whose outlet is heated above the solidification temperature of aluminum, there is no opportunity for new crystal nucleation during casting, and the crystals are formed by growth competition. Easily becomes a single crystal by reducing the number. That is, it is possible to obtain a uniform ingot having no crystal solidification grain boundaries that cause uneven formation of an oxide film.

As a continuous casting method for single crystal ingots, for example, as shown in FIG. 1, there is a method of continuous casting using a mold whose outlet temperature is heated to a temperature higher than the solidification temperature of the cast metal. 1st
In the figure, a mold (2) with a built-in heater (2) is heated to a temperature higher than the solidification temperature of the cast metal. The ingot (2) pulled out of the mold (2) is cooled by the cooling water (2), and the ingot (2) in Figure 0 avoids the inner wall surface of the mold (2) at the solidification interface and plunges into the molten metal (2) in the mold.

The ingot thus obtained reduces the number of grain boundaries as casting progresses and easily becomes a single crystal ingot. Further, by providing a single crystal seed at the tip of the ingot dummy, it is possible to easily form a single crystal ingot. When the single crystal ingot obtained in this way is rolled into foil, unlike conventional ingots, there is no edge cracking of the plate or foil during rolling, and the product yield rate is 100%. Furthermore, since there are no grain boundaries where impurities tend to accumulate even in surface oxidation treatment of the foil, an oxide film can be formed uniformly on the surface of the foil. This indicates that it is possible to make the oxide film thinner than before, and that it is possible to make the electrolytic capacitor itself smaller.

According to the present invention, not only is it not necessary to repeatedly perform electrolytic refining to remove impurity elements or perform zone melting which is poor in productivity, but also it is possible to uniformly distribute impurity elements in the ingot. Therefore, conventional industrial pure aluminum can be used sufficiently as a capacitor foil. Furthermore, since edge cracking does not occur during rolling, the yield is significantly improved and the process is extremely economical compared to conventional methods using ingots made of polycrystalline bodies.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a casting method for continuously casting a single crystal ingot.

Claims (1)

[Claims] 1. A method for producing aluminum foil for electrolytic capacitors, in which the foil is obtained by rolling an aluminum ingot, the aluminum ingot being heated to a temperature of 660° C. or higher at the outlet. 1. A method for manufacturing aluminum foil for electrolytic capacitors, characterized by continuous casting using a mold. 2. The method for producing aluminum foil for an electrolytic capacitor according to claim 1, wherein the aluminum ingot is made of a single crystal.