JPH01256A - Manufacturing method of aluminum foil for electrolytic capacitors - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing aluminum foil for electrolytic capacitors that provides high capacitance after AC etching.

[Conventional technology] The capacitance of an electrolytic capacitor is proportional to the surface area of the electrodes.

Therefore, aluminum foil for electrodes is chemically or electrochemically etched and roughened to increase its surface area. Etching conditions are determined by the final use of the foil.

For electrodes of electrolytic capacitors that are chemically converted to a low voltage or not chemically formed at all during use, AC etching is widely used in Japan because it produces uniform and fine etch bits of about 0.5 μm.

Both hard and soft aluminum foils are used for AC etching, but hard foils are superior in terms of strength. Therefore, hard materials are advantageously used because they allow high tension to be applied to the etching line and cause fewer problems such as meandering, foil breakage, and wrinkles during etching.

Further, intermediate annealing is not performed during the rolling process of the foil base and foil. Usually, intermediate annealing is carried out to soften the rolled material when it becomes work hardened and becomes difficult to roll. However, foil material for electrolytic capacitors has a high aluminum purity, making it difficult to roll. This is because it does not harden until it becomes solid.

[Problems to be Solved by the Invention] When a hard aluminum foil is subjected to AC electrolytic etching, a spongy structure in which etch pits of about 0.5 μm are gathered is formed.

By the way, the weight of aluminum foil is reduced by AC etching due to the following three factors.

■　Electrolytic etching weight loss: between reaction zones by AC electrolysis.

■Chemical dissolution weight loss: Weight loss due to chemical reaction with electrolyte.

■ Weight loss due to mechanical shedding: Weight loss due to loss of spongy tissue.

Among these, ■ is proportional to the amount of electricity flowing and shows a value that is the same as the theoretical value. Also, ■ has a strong relationship with the components of the aluminum foil.

The present inventors have recently discovered that ■ is closely related to the manufacturing conditions of aluminum foil.

Therefore, the present invention attempts to obtain a high capacitance by investigating the relationship between the amount of weight loss during AC etching and the capacitance.

[Means for Solving the Problems] The present invention heats aluminum with a purity of 99.4% or more to an annealing temperature immediately after hot rolling or during cold rolling to achieve a final cold rolling rate of 50 to 99%. This is a method for manufacturing aluminum foil for electrolytic capacitors, characterized by:

That is, the present invention relates to rolling high-purity aluminum,
Immediately after hot rolling or during cold rolling, heating is performed at a normal intermediate annealing temperature of 250°C to 620°C to control the amount of strain in the final rolled foil and control the density of pits generated during AC etching. , which prevents the pits from coalescing into each other and mechanically falling out.

The reason why the aluminum purity is set to 99.4% or more is because if the purity is lower than this, there are too many impurities and it is not suitable for the electrode of a capacitor. Further, the minimum value of the cold rolling rate is set within a range in which hard aluminum can be obtained.

Then, tests were conducted on the cold rolling rate of aluminum foil (99,98% AI), the capacitance after AC etching, and the amount of weight loss during AC etching, and the results shown in Figures 1 and 2 were obtained. Ta.

In other words, Figure 1 shows the relationship between the cold rolling rate, capacitance, and weight reduction rate of a product that has been chemically treated at 40V. As the rolling rate increases, the pit density during AC etching increases, and when it exceeds the limit, the pits begin to coalesce, increasing the amount of weight loss due to mechanical dropout mentioned above, and reducing the capacitance. This is considered to indicate that FIG. 3 is a graph showing the relationship between weight loss and capacitance in the case of FIG. 1. FIG. 2 is a graph showing the relationship between cold rolling rate, capacitance, and weight reduction rate when subjected to 20V chemical conversion treatment. In the case of this low-voltage forming, fine etch pits are effective, and in particular, in the case of high-voltage forming, an improvement in capacitance is observed in the range of a cold rolling rate of 95% or more where the capacitance decreases.

Therefore, in the present invention, the chemical conversion voltage is changed as appropriate depending on the intended use of the foil, and the cold rolling rate is also changed within the above range to obtain a product with desired characteristics.

[Example] Next, Examples will be shown. Examples 1 to 4 and Comparative Example 1.2
Examples 5 to 8 and Comparative Examples 3 to 6 are examples in which the cold rolling rate is up to 95%, and Examples 5 to 8 and Comparative Examples 3 to 6 are examples in which the cold rolling rate is 95% or more.

Example 1 Si: 50ppm SFe: 50ppm,
Cu: 99 containing 35 ppm and other unavoidable impurities
．． Using 98% aluminum, the slab was homogenized and hot rolled in a conventional manner to produce a plate with a thickness of 25 mm.

This 25mIII plate was cold-rolled to a thickness of 0.5 mm, and then intermediately annealed at 350° C. for 1 hour. Thereafter, it was rolled to a thickness of 0.1 mm to obtain a foil for etching.

Example 2 After cold rolling the same 25 mm plate as in Example 1 to a 1.5 mm thick plate, a 1 mm thick foil was created using the same operations as in Example 1 except that intermediate annealing was performed. .

Comparative Example 1 A 25 mm thick plate made in the same manner as in Example 1 was made into a 0.1 mm thick foil without intermediate annealing.

Example 3 A foil with a beating thickness of 0.1 was made in the same manner as in Example 2 except that 99.85% aluminum containing 3i: 0.05%, Fe: 0.07% and other unavoidable impurities was used. did.

Example 4 A foil with a thickness of 0.1 mm was produced in the same manner as in Example 3, except that intermediate annealing of a thickness of 1.5 mm was performed at 520° C. for 10 seconds.

Comparative Example 2 A foil with a thickness of 0.1 mm was produced in the same manner as in Example 3, except that intermediate annealing was performed at a thickness of 6 mm.

Example 1 The hard foil with a thickness of 0.1 mm obtained as described above was heated at 0.6 A/cm 2 in an electrolytic solution of 12.5% hydrochloric acid and 0.6% phosphoric acid at 55°C. AC etching was performed at 60 Hz for 3 minutes for Examples 3 and 2 and Comparative Example 1, and for 1 minute for Examples 3 and 4 and Comparative Example 2.

Thereafter, Examples 1 and 2 and Comparative Example 1 were converted to 40 V in an ammonium adipate aqueous solution, and Examples 3 and 4 and Comparative Example 2 were converted to 3 V, and the capacitance was increased in an ammonium borate aqueous solution. It was measured.

Further, the amount of weight loss due to AC etching was calculated from the weight difference before AC etching.

Table 1 shows the capacitance thus obtained and the amount of weight loss during AC etching.

Table 1 Example 5 A 25 mm thick plate produced in the same manner as in Example 1 was cold rolled to a thickness of 2.5 mm, and then intermediate annealed at 350° C. for 1 hour. Thereafter, it was rolled to 0.1111 m to obtain a foil for etching.

Example 6 A foil with a thickness of 0.1 mm was prepared in the same manner as in Example 5, except that the same 25 mm thick plate as in Example 5 was cold-rolled to a thickness of 5 mm+, and then subjected to intermediate annealing.

Comparative Example 3 A 0.1 mm thick foil was produced from a 25 mm thick plate produced in the same manner as in Example 5 without performing intermediate annealing.

Comparative Example 4 A 25 mm thick plate produced in the same manner as in Example 5 was cold-rolled into an im-thick plate, and then a 0.1 mm thick foil was produced in the same manner as in Example 5, except that intermediate annealing was performed. Created.

Example 7 A 0.1 mm thick foil was created in the same manner as in Example 5 except that 99.85% aluminum containing 3i: 0.05%, Fe: 0.07% and other unavoidable impurities was used. .

Example 8 A foil with a thickness of 0.1 mm was produced in the same manner as in Example 7, except that intermediate annealing was performed at a thickness of 5 mm.

Comparative Example 5 A 25 mm thick plate made in the same manner as in Example 7 was made into an o.imm thick foil without intermediate annealing.

Comparative Example 6 A foil with a thickness of 0.1 mm was produced in the same manner as in Example 7, except that intermediate annealing was performed at a thickness of 1 mm.

0 obtained in Examples 5 to 8 and Comparative Examples 3 to 5 above,
A 1 mm thick hard foil was diluted with 1% in 12.5% hydrochloric acid at 55°C.
Examples 5 and 6 and Comparative Examples 3 and 4 at 0.8 A/Cm 2 in an electrolyte containing nitric acid, 0.5% phosphoric acid, and 0.7% oxalic acid.
AC etching was performed at 60 Hz for 3 minutes for Examples 7 and 8 and Comparative Examples 5 and 6 for 1 minute.

Thereafter, Examples 5 and 6 and Comparative Examples 3 and 4 were converted to 20V in an ammonium adipate aqueous solution, and Examples 7 and 8 and Comparative Examples 5 and 6 were converted to 3V, and then left to stand in an ammonium borate aqueous solution. The capacitance was measured.

The amount of weight loss due to AC etching was calculated from the difference in weight before and after AC etching.

Table 2 shows the capacitance thus obtained and the amount of weight loss during AC etching.

Table 2 [Effects of the Invention] The present invention makes it possible to obtain an aluminum foil that can have a high capacitance (q) when used for electrolytic capacitors by adjusting the state of etch pit formation during AC etching. can.

This has the effect of reducing the dissolved aluminum concentration in the electrolytic solution of the electrolytic capacitor and slowing down the deterioration of the solution.

[Brief explanation of drawings]

Figure 1 is a graph showing the test results regarding the relationship between cold rolling rate during 40V chemical conversion treatment, weight loss during AC etching, and capacitance, and Figure 2 is a graph showing the relationship between cold rolling rate and capacitance during 20V chemical conversion treatment. A graph showing the test results on the relationship between the amount of weight loss during AC etching and capacitance, and Figure 3 shows the test results on the relationship between the amount of weight loss and capacitance during AC etching in Figure 1. It is a graph. Patent Applicant Sumitomo Light Metal Industries Co., Ltd. Agent Patent Attorney Hide Komatsu Agent Patent Attorney Hiroshi Asahi

Claims (1)

[Claims] A method for producing aluminum foil for electrolytic capacitors, which comprises heating aluminum with a purity of 99.4% or more to an annealing temperature immediately after hot rolling or during cold rolling to achieve a final cold rolling rate of 50 to 99%. .