JPH04224661A - Manufacture of aluminum foil for electrode in electrolytic capacitor - Google Patents

Abstract

PURPOSE:To offer the manufacturing method of an aluminum foil, with which an electrode foil for electrolytic capacitor having high electrostatic capacity is manufactured by using aluminum material incorporating comparatively much impurities of Fe, Si, etc. CONSTITUTION:Aluminum cast ingot having 99.93-99.98% purity of the aluminum is prepared. To this cast ingot, homogeneous treatment is executed in the condition of 530-630 deg.C and 5-24hr holding time. Thereafter, hot rolling is executed in the condition of >=550 deg.C starting temp. and <=300 deg.C finishing temp. to manufacture the aluminum plate. To this aluminum plate, cold-rolling is executed at <=80 deg.C. Before or on the halfway of cold-rolling, intermediate annealing is not executed. To the aluminum sheet obtd. with the cold-rolling, finish-annealing is executed in the condition of 320-480 deg.C and 10-30hr. After completing the finish-annealing, the aluminum sheet is cooled in the condition of >=15 deg.C/hr cooling velocity to obtain the aluminum foil for electrode in the electrolytic capacitor.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing aluminum foil for electrolytic capacitor electrodes using an aluminum material containing relatively many impurities.

0002

2. Description of the Related Art The method of manufacturing aluminum foil for electrolytic capacitor electrodes is basically the same as that of general aluminum foil. That is, the method for producing aluminum foil for electrolytic capacitor electrodes involves the step of creating an ingot from an aluminum base metal, and heating the ingot at a temperature of 500 to 600°C for 1 to 2 hours.
Homogenization process heating for 4 hours, temperature 350-550℃
The process consists of hot rough rolling at a temperature of 250 to 400°C, hot finish rolling at a temperature of 250 to 400°C, repeated cold rolling at room temperature, and optionally intermediate or final annealing at a temperature of 300 to 600°C. be.

However, impurities, especially Fe and Si
When aluminum foil for electrolytic capacitor electrodes is manufactured using this method using aluminum metal containing a large amount of
An electrode foil with high capacitance could not be obtained. This is because excessive dissolution occurs during etching during electrode foil production. In other words, when overdissolution occurs, large pores are formed on the surface of the foil,
The surface area of the foil cannot be sufficiently expanded, and therefore an electrode foil with high capacitance cannot be obtained.

For this reason, impurities (Fe and Si
) The aluminum foil for electrolytic capacitor electrodes is manufactured by the method described above using an aluminum base metal with extremely low content. By using an aluminum base metal with low impurities, it is difficult for impurities to precipitate into the resulting aluminum foil for electrolytic capacitor electrodes, and over-dissolution is less likely to occur during etching, resulting in the resulting electrode foil also exhibiting high capacitance. It turns out.

[0005]

[Problems to be Solved by the Invention] However, aluminum ingots with extremely low impurities are obtained through a special refining process and are expensive. In particular, it is difficult to purify Al to remove impurities such as Fe and Si, and the resulting high-purity aluminum ingot has to be extremely expensive. As described above, since the raw materials are expensive, the resulting aluminum foil for electrolytic capacitor electrodes is also expensive. Furthermore, when the purity of the aluminum foil itself becomes high, the strength of the material essentially decreases, making it impossible to obtain a high-strength aluminum foil for electrodes.

[0006] Therefore, the present invention uses an aluminum ingot that contains relatively many impurities and subjects it to homogenization treatment, hot rolling, cold rolling, finish annealing, etc. under certain specific conditions. The object of the present invention is to provide an aluminum foil for electrolytic capacitor electrodes that is low in price, has high strength, and has high capacitance.

[0007]

[Means for Solving the Problems] That is, the present invention subjects an aluminum ingot having an aluminum purity of 99.93 to 99.98% to homogenization treatment at a temperature of 570 to 630°C for a period of 5 to 24 hours. After that, an aluminum plate is created by hot rolling at a starting temperature of 550°C or higher and a finishing temperature of 300°C or lower, and then cold rolling is performed on the aluminum plate at a temperature of 80°C or lower without intermediate annealing. to obtain an aluminum thin plate, and then the aluminum thin plate was heated to a temperature of 320 to 4
An aluminum foil for electrolytic capacitor electrodes, characterized by subjecting the aluminum foil to final annealing at 80°C for 10 to 30 hours, and further cooling the aluminum thin plate at a cooling rate of 15°C/hr or more after finishing the final annealing. This relates to a manufacturing method.

The aluminum purity of the aluminum ingot used in the present invention is 99.93 to 99.98%. If the aluminum purity is less than 99.93%, even if homogenization treatment is performed under the above-mentioned specific conditions, an aluminum foil that can be used to create a high capacitance electrode foil cannot be obtained.
Undesirable. Moreover, if the aluminum purity exceeds 99.98%, it is not preferable because a low-cost and high-strength aluminum foil, which is the object of the present invention, cannot be obtained.

[0009] This aluminum ingot is subjected to homogenization treatment. The conditions for the homogenization treatment are a temperature of 570 to 630°C. If the temperature condition of the homogenization treatment is lower than 570° C., impurities will not be sufficiently dissolved in the aluminum and an electrode foil with high capacitance will not be obtained, which is not preferable. Furthermore, if the temperature condition exceeds 630°C, the aluminum ingot may blister or partially melt, which is not preferable. Furthermore, the aluminum ingot undergoes creep deformation, making rolling difficult, which is undesirable. In addition,
It is generally preferable to face the aluminum ingot before applying the homogenization treatment.

[0010] Furthermore, the homogenization treatment time is 5 to 24 hours. If the homogenization treatment time is less than 5 hours, impurities will not be sufficiently dissolved in the aluminum and an electrode foil with high capacitance will not be obtained, which is not preferable. On the other hand, if the homogenization treatment time exceeds 24 hours, productivity will decrease and the resulting aluminum foil will become expensive, which is not preferable.

[0011] After homogenizing the aluminum ingot under the above conditions, it is hot rolled. The conditions for hot rolling are that the starting temperature is 550°C or higher and the ending temperature is 300°C.
It is as follows. If the starting temperature is less than 550° C., impurities dissolved in solid solution during the homogenization treatment may precipitate, making it impossible to obtain an electrode foil with high capacitance, which is not preferable. Furthermore, if the finishing temperature exceeds 300°C, impurities in the aluminum may precipitate before the cold rolling process begins, making it impossible to obtain an electrode foil with high capacitance, which is not preferable.

[0012] After hot rolling an aluminum ingot to produce an aluminum plate, this is cold rolled. Cold rolling is performed at a temperature of 80° C. or lower. 80 cold rolled
If the temperature exceeds .degree. C., impurities dissolved in aluminum may precipitate, making it impossible to obtain an electrode foil with high capacitance, which is not preferable. Then, intermediate annealing is not performed before this cold rolling or during the cold rolling. Intermediate annealing is not preferable because it reduces the strength of the aluminum sheet obtained by cold rolling. Also,
This is not preferred because the number of steps increases and the resulting aluminum foil becomes expensive. Furthermore, depending on the conditions of intermediate annealing, impurities may precipitate and the capacitance of the resulting electrode foil may decrease.

Next, the aluminum thin plate obtained by cold rolling is subjected to finish annealing. The temperature conditions for final annealing are 320 to 480°C. If finish annealing is performed at a temperature lower than 320° C., the impurities in the aluminum will not be sufficiently solid-dissolved again, and the capacitance of the resulting electrode foil will decrease, which is not preferable. On the other hand, if the final annealing is performed at a temperature exceeding 480° C., the aluminum will be oxidized, the etching performance will deteriorate, and the capacitance of the resulting electrode foil will decrease, which is not preferable. Furthermore, there is a risk that the strength of the resulting aluminum foil may decrease, or that the aluminum foils may stick to each other if finish annealing is performed in a laminated state.

[0014] Further, the time for final annealing is 10 to 30 hours. When the final annealing time is less than 10 hours,
This is not preferable because the re-solid solution of impurities in aluminum is insufficient and the capacitance of the obtained electrode foil is reduced. On the other hand, it is not preferable to perform finish annealing for more than 30 hours because this only reduces the production rate and makes the resulting aluminum foil expensive.

[0015] After finishing this final annealing, the aluminum foil is cooled. This cooling rate is 15° C./hr or more. If the cooling rate is less than 15° C./hr, impurities re-dissolved in the aluminum may precipitate, making it impossible to obtain an electrode foil with high capacitance, which is not preferable.

The aluminum foil for electrolytic capacitor electrodes obtained as described above is subjected to an etching treatment to form a large number of micropores on the surface of the foil. The electrode foil obtained in this manner has a high surface area expansion rate and has a high capacitance.

[0017]

[Example] Prepare aluminum ingots with the purity listed in Tables 1 and 2, and have a thickness of 35 mm, a width of 180 mm, and a length of 18 mm.
Molten metal was poured into a 0 mm book mold to obtain an aluminum ingot. Both sides of this aluminum ingot were face milled by 2 mm. Then, it was placed in a furnace in an atmospheric atmosphere and subjected to homogenization treatment under the conditions shown in Tables 1 and 2. Thereafter, hot rolling was performed under the conditions shown in Tables 1 and 2 to obtain an aluminum plate. This aluminum plate was cold rolled under the temperature conditions shown in Tables 1 and 2 to obtain a 90μ thin aluminum plate, and
and under the conditions shown in Table 2 and in a vacuum or non-oxidizing atmosphere,
Finish annealing was performed to obtain an aluminum foil.

This aluminum foil was subjected to electrolytic etching under the etching conditions shown below. The capacitance and tensile strength of this etched foil were measured. The capacitance was measured using an LCR meter in an 8.0% boric acid aqueous solution at room temperature after chemical conversion treatment in an 8.0% boric acid aqueous solution at a liquid temperature of 70°C. The capacitance and tensile strength are shown in Tables 1 and 2. As can be seen from this result, the aluminum foil obtained by the method according to the example exhibits higher values in both capacitance and tensile strength than the aluminum foil obtained by the method according to the comparative example.

[0019]

[Effects of the Invention] As explained above, if aluminum foil for electrolytic capacitor electrodes is manufactured by the method according to the present invention,
Even if aluminum contains relatively large amounts of impurities such as Fe and Si, an aluminum foil with excellent etching properties can be obtained. Therefore, by using this aluminum foil, it is possible to obtain a high capacitance electrode foil for electrolytic capacitors. Moreover, the aluminum foil for electrolytic capacitor electrodes obtained by the method according to the present invention also has the advantage of having higher tensile strength than the aluminum foil for electrolytic capacitor electrodes obtained using high-purity aluminum.

[0020] Therefore, if the method according to the present invention is adopted,
An electrode foil for an electrolytic capacitor having a high capacitance can be obtained using low-purity aluminum, and the electrode foil can be manufactured at a low cost. Further, an electrode foil for an electrolytic capacitor having high tensile strength can be obtained, and the electrode foil is less likely to break during assembly of an electrolytic capacitor.

[Table 1]

[Table 2]

Claims (1)

[Claims] [Claim 1] Aluminum purity 99.93-99.
A 98% aluminum ingot is homogenized at a temperature of 570 to 630°C for 5 to 24 hours, and then hot rolled at a starting temperature of 550°C or higher and a finishing temperature of 300°C or lower. An aluminum plate is prepared, and then the aluminum plate is cold rolled at a temperature of 80°C or less without intermediate annealing to obtain an aluminum thin plate, and then the aluminum plate is rolled at a temperature of 320 to 480°C for 10 to 30 hours. Finish annealing is performed under the following conditions, and after finishing the finish annealing,
A method for producing aluminum foil for electrolytic capacitor electrodes, which comprises cooling an aluminum thin plate at a cooling rate of 15° C./hr or more.