JPH0637697B2 - Annealing treatment method for aluminum foil coil for electrolytic capacitor electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an annealing treatment method for an aluminum foil coil for an electrolytic capacitor electrode, and more particularly to improvement of an annealing treatment method which is carried out in advance in order to improve etching characteristics.

In this specification, the term aluminum is used to include this alloy.

Conventional technology Aluminum foil for electrolytic capacitor electrodes is generally subjected to electrochemical or chemical etching in order to expand the effective area and increase the capacitance per unit area, but in order to improve the etching function. It is conventional to anneal the foil prior to etching.
This annealing is generally carried out in the annealing furnace, until the aluminum coil is completed.

Conventionally, the above-described annealing has been performed by vacuum annealing in which heating is started when a predetermined vacuum degree is reached after evacuation by a vacuum pump or the like. However, it turns out that such a method has the following drawbacks.

Problems to be Solved by the Invention That is, in the process of vacuuming, as a result of leaving gaps between the layers of the aluminum coil, especially at the ends, air remains unevenly,
Not only the coil end portion is deformed and the appearance shape is poor, but also a non-uniform and thick oxide film is formed on the end surface, and the oxide film hinders sufficient etching performance, resulting in a satisfactory capacitance. There was a drawback that you could not get. For this reason, since the coil end cannot be practically used as a product, there is a drawback in that the end is conventionally cut off, resulting in poor yield.

The present invention has been made to solve the above-mentioned drawbacks, and prevents the occurrence of gaps between the layers at the coil end as much as possible and prevents the decrease in the capacitance at the coil end to prevent It is an object of the present invention to provide an annealing treatment method for an aluminum foil coil for an electrolytic capacitor electrode, which is capable of obtaining a uniform and large electrostatic capacitance over the entire width direction.

Means for Solving the Problems For the above-mentioned object, the present invention is to start heating in an inert gas atmosphere prior to vacuum annealing, and then, at the time when the atmospheric temperature reaches 250 to 350 ° C., perform instantaneous depressurization. Speed 38T
The method is characterized in that vacuuming is performed at a pressure reduction rate of orr / min or less, and then vacuum annealing is performed.

The outline of the annealing process according to the present invention is shown in FIG. 1 as a process diagram.

In the figure, the curve (A) shows the state of change of the atmospheric pressure in the furnace, and the curve (B) shows the state of change of the temperature in the furnace due to heating.

The inert gas atmosphere is formed by first evacuating the furnace from atmospheric pressure and then introducing an Ar gas-based inert gas. The initial evacuation is to evacuate the inside of the furnace from atmospheric pressure to a vacuum degree of about 10 ^-2 Torr. In this process as well, a gap is not generated between the end layers of the aluminum foil coil as much as possible. Therefore, the exhaust process from the atmospheric pressure (760 Torr) to the vacuum degree of at least about 10 Torr is
It is desirable to perform the maximum instantaneous depressurization rate under the condition of 38 Torr / min or less. Further, the inert gas atmosphere pressure is preferably set to 1 Torr or more in order to further reduce the generation of the gap at the edge portion of the coil.

The heating for annealing starts at the same time when the inert gas atmosphere is formed.

After the heating is started, the ambient temperature in the furnace gradually rises. Therefore,
Vacuuming is started when the ambient temperature (T) reaches 200 to 350 ° C. This evacuation is an instantaneous decompression speed of 38T
It is necessary to perform at a slow pressure reduction rate of orr / min or less. When vacuuming is performed at a depressurization rate of more than 38 Torr / min, a gap is created between the coil end layers, and oxygen remaining in the furnace mixes into the gap to form an oxide film on the aluminum foil surface. The etching characteristics are deteriorated, and the capacitance is lowered. Further, the vacuuming start temperature (T) is limited to 200 to 350 ° C., but if the temperature is less than 200 ° C., the cause is not clear, but there is a tendency to form a gap between the end layers of the aluminum foil coil. Yes, if the temperature exceeds 350 ° C, the end of the coil,
This is because the etching characteristics of the aluminum foil are deteriorated in all the central portions, and eventually the capacitance is lowered as a whole. It is preferable to perform evacuation until the degree of vacuum reaches 1 × 10 ⁻³ Torr or less, because a larger electrostatic capacity can be obtained.

After that, heating is further continued while maintaining a required degree of vacuum, and vacuum annealing is performed according to a conventional method, for example, a maximum temperature of 530 to 5
Annealing treatment is performed at 70 ° C. for about 1 hour.

EFFECTS OF THE INVENTION As described above, according to the present invention, when the aluminum foil coil for electrolytic capacitor electrodes is annealed, after heating is started in an inert gas atmosphere, the ambient temperature is 200 to 35.
When the temperature reaches 0 ° C., the vacuum depressurization is performed at an instantaneous depressurization rate of 38 Torr / min or less, and then vacuum annealing is performed, thereby forming a gap at the winding end of the coil. Therefore, a good annealing treatment effect can be exerted uniformly over the entire width of the coil without causing harmful deformation of the edge portion. Although the reason why such an effect can be achieved is not clear, by treating the initial stage of heating in an inert gas atmosphere,
The atmospheric pressure applied to the coil from the outside cancels out the gas pressure acting outward from inside the coil, preventing the formation of gaps between the winding layers of the coil during the initial stage of heating, and during the vacuum annealing process. In the above, since the temperature of the coil itself has already risen to a considerable extent, the gas pressure acting from the inside of the coil to the outside is small, and the pressure acts to generate a gap between the winding layers. It is presumed that this is due to nothing.

As described above, the uniform annealing process can be completed without creating a gap at the edge of the coil, so that the entire surface can be etched evenly in the subsequent etching process, which in turn increases the capacitance. In addition, since there is no shape defect or annealing defect due to the formation of the gap at the winding end of the coil, it is not necessary to cut off the winding end as in the conventional case, the yield can be improved, and the product cost can be reduced. It can be reduced.

Example Next, an example of the present invention will be shown in comparison with a conventional example by a conventional method and a comparative example.

(Examples / Comparative Examples) A coil made of an aluminum foil having a purity of 99.99%, a thickness of 100 μm and a length of 1000 m was used, each coil was set in an annealing furnace, and then the furnace was evacuated by a vacuum pump. . At this time, 1 from atmospheric pressure (760 Torr)
The evacuation until reaching the vacuum degree of 0 Torr was performed by adjusting the pressure reduction rate to about 20 Torr / min, and then further evacuation was performed to make the inside of the furnace a vacuum of about 10 ^-2 Torr.

At this point, the heating of the furnace was started, and at the same time, the introduction of Ar gas was started into the furnace, and the internal atmosphere of the furnace was maintained under the inert gas atmosphere of about 50 Torr under the control of the vacuum pump.

Then, in the range until the temperature in the furnace reaches 100 to 500 ° C., the time when the temperature is raised to various set temperatures of 50 ° C. is selected as the vacuum annealing start time, and the temperature in the furnace is set to 38 Torr.
Vacuum reduction is started at a decompression rate of less than or equal to 15 minutes / minute, and particularly at an instantaneous decompression rate of about 15 Torr / minute, and finally 10 ^-4 T
The vacuum degree was set to orr.

Then, by continuing the heating in this vacuum atmosphere, a vacuum annealing treatment of 550 ° C. × 1 hour is performed,
Thereafter, an annealed aluminum foil coil was obtained according to a conventional method.

Then, for each annealed coil, by visual observation,
The presence or absence of a gap in the edge portion was checked, and the aluminum foil obtained from the coil central portion and the edge portion was used as a sample, which was subjected to etching treatment, and then the capacitance of each sample was measured. Etching is performed under the conditions of a treatment liquid: 5 wt% hydrochloric acid, a liquid temperature: 80 ° C., a current density: DC10 A / dm ² , and an etching time: 6 minutes. Capacitance is obtained by converting the etching foil to 230 V in an aqueous boric acid solution. It was measured. The results are shown in Table 1.

(Conventional example) Vacuuming is performed in a furnace in which the same coil as that described above is set (initial depressurization rate is 200 Torr / min), and the inside of the furnace is finally set to a vacuum degree of 1 × 10 ⁻⁴ Torr, and then in the vacuum. Heating was started and heat treatment was performed at 550 ° C. for 1 hour.

The samples thus obtained were observed and measured in the same manner as in the above-mentioned Examples and Comparative Examples, and the results are shown in comparison with Table 1.

As is clear from the results of Table 1 above, according to the present invention, it is possible to prevent the formation of gaps at the coil end portions, and accordingly, to achieve the same etching as the central portion up to the coil end portions. It was confirmed that it is possible to impart characteristics and to have an excellent capacitance.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the pressure control state in the furnace and the temperature change state due to heating during the annealing process according to the present invention with time.

Claims (3)

[Claims] 1. When annealing an aluminum foil coil for an electrolytic capacitor electrode, after heating in an inert gas atmosphere, when the atmospheric temperature reaches 200 to 350 ° C., the instantaneous depressurization rate is 38 Torr / min or less. A method for annealing an aluminum foil coil for an electrolytic capacitor electrode, which comprises performing vacuuming at a reduced pressure rate and then performing vacuum annealing. 2. The method for annealing an aluminum foil coil for an electrolytic capacitor electrode according to claim 1, wherein the inert gas atmosphere pressure is set to 1 Torr or more. 3. The atmospheric pressure during vacuum annealing is 1 × 10 ⁻³ To.
The annealing treatment method for an aluminum foil coil for an electrolytic capacitor electrode according to claim 1 or 2, which is rr or less.