JPH0260048B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a cathode material for electrolytic capacitors. Conventional Technology Electrode materials for electrolytic capacitors are generally divided into anode materials and cathode materials, but in order to increase the capacitance of a capacitor, it is necessary to improve the electrostatic capacity not only of the anode material but also of the cathode material itself. It is also important to improve capacity. As one of the cathode materials designed to improve capacitance, there is a known material in which a metal film such as a titanium film is formed on the surface of an aluminum box base material by vapor deposition in an inert gas (for example, Unexamined Japanese Patent Publication 1987
−167009). According to this cathode material, fine irregularities are formed on the surface of the film, and as a result, the area expansion ratio is improved compared to conventional cathode materials in which the surface area is enlarged by etching aluminum foil. Therefore, it is possible to further increase the capacitance. Problems to be Solved by the Invention However, even with the above-mentioned cathode materials, there is still a limit to the expansion of the surface area with a metal film, which is currently required to realize smaller size and higher performance of electrolytic capacitors. This did not give sufficient satisfaction to the increase in capacitance. The present invention was made in view of the above circumstances, and an object of the present invention is to provide a cathode material with further increased capacitance. Means for Solving the Problems For this purpose, the inventors conducted various experiments and research, and found that while the surface of the base material was roughened to form fine irregularities, a large number of pores were formed on the surface. After further expanding the surface area of the base material by distributing it as densely as possible, a titanium vapor deposited film made of titanium fine particles is further formed on the surface, thereby reducing electrostatic charge. It was discovered that the capacity could be significantly increased, leading to the completion of this invention. That is, this invention provides that pores with a maximum depth of 25 μm or less and a maximum internal diameter of 100 μm or less are distributed in the surface of a finely roughened aluminum foil base material at a density of 100 pores/cm ² or more, and The gist of the present invention is to provide a cathode material for an electrolytic capacitor, characterized in that at least the surface portion of the base material excluding the pores is coated with a titanium vapor-deposited film. In this specification, the term aluminum is used to include aluminum alloys. The reason why the surface of the aluminum foil base material 1 is roughened to form the fine irregularities 3 is to spread the roughness effect to the surface of the titanium vapor deposited film 2 formed on the base material, thereby expanding the surface of the film. This is to help improve the ratio. Furthermore, the reason why a large number of pores 4 are formed in the base material 1 is to further expand the surface area of the base material and to improve the wettability of the electrolytic solution. Such roughening of the surface of the base material and formation of the pores 4 can be achieved simultaneously by an etching operation. For such etching, it is possible to employ not only a chemical or electrochemical wet etching method but also a dry etching method. Typical cross-sectional shapes of the pore 4 include a cylindrical shape with an approximately constant inner diameter regardless of the depth, as shown in Figure 2 A, B, and C;
Examples include a pot shape with a narrow inner diameter of the opening, and a bowl shape with an inner diameter increasing from the bottom to the opening. The dimensions of the pore 4 need to be a maximum depth of 25 μm or less and a maximum internal diameter of 100 μm or less. If the maximum depth exceeds 25 .mu.m or the maximum inner diameter exceeds 100 .mu.m, the disadvantage arises that it becomes difficult for the base material 1 to maintain the required mechanical strength as a cathode material. In addition, in order to increase the area expansion ratio of the base material 1, the pores 4 should have relatively small diameters and should be distributed as densely as possible, with a density of at least 100 pores/cm ² .
It is necessary to make the distribution at a density of at least a certain level. Although the inner surface of the pore 4 does not necessarily have to be roughened, it is preferable that the inner surface also be formed into a finely uneven and rough surface in order to increase the capacitance. In this specification, the fine irregularities due to surface roughening refer to microscopic irregularities that do not include pores on the surface of the base material, as well as waviness components on the same surface. The material of the conductive film formed on the surface of the base material 1 is particularly limited to titanium because it can be made to be more durable than other conductive metals such as iron and copper. This is because it is possible to further extend the life of the capacitor and achieve higher reliability. As shown in FIG. 1, this titanium vapor-deposited film 2 needs to be formed on the entire surface of the base material 1 except for at least the pores 4, but of course,
It is preferable to form a coating on the inner surface of the pore 4 at the same time, since the capacitance can be further increased. The average particle diameter of the titanium fine particles constituting such a film is 0.01 to 1.0 μm from the viewpoint of improving the area expansion ratio of the film.
It is desirable that the range be within the range of In other words, if the thickness is less than 0.01 μm, the film becomes smooth and contributes little to the surface-enlarging effect, and conversely, if it becomes coarser than 1.0 μm, the surface-enlarging effect is poor and the capacitance is small. This is because it will be put away. Further, the thickness of the film is preferably in the range of 0.05 to 5.0 μm.
This is because if the thickness is less than 0.05 μm, the effect of surface expansion due to roughening of the film cannot be expected, whereas if it exceeds 5.0 μm, the effect is worth the increase in the amount of titanium material used, the increase in cost, and the deterioration of workability. This is because it cannot be obtained. As a method for forming such a titanium vapor-deposited film 2 on the surface of the base material 1, a vacuum vapor deposition method, an inert gas vapor deposition method, a sputtering method, an ion plating method, etc. can be used. Incidentally, such a process for forming a titanium film by vapor deposition can be performed semi-continuously while winding up a coiled base material. Effects of the Invention The cathode material for electrolytic capacitors according to the present invention is
As described above, not only is the surface of the base material roughened, but pores with a maximum depth of 25 μm or less and a maximum internal diameter of 100 μm or less are distributed on the surface at a density of 100 pores/cm ² or more. Because of this, the surface area of the base material itself is further expanded compared to conventional cathode materials that use base materials with smooth surfaces or simply roughened surfaces with minute irregularities. In addition, since a titanium vapor-deposited film is formed on at least the surface of the base material excluding the pores, the film has an effect of expanding the surface area, which makes it more durable than conventional products. This can significantly increase the capacitance. Therefore, it is possible to further reduce the size and improve the performance of the electrolytic capacitor. Additionally, by using a base material with many pores on the surface, the wettability of the electrolyte to the cathode surface becomes even better, which in turn improves the durability and retention of initial performance of the capacitor. . In addition, the fact that the conductive film on the surface is made of a titanium vapor-deposited film makes it more durable than those using other metals.
As described above, according to the present invention, not only the capacitance of the capacitor can be increased and the capacitor can be made smaller, but also a longer life and higher reliability can be realized. Examples Next, examples of the present invention will be shown together with comparative examples. Example 1 Aluminum foil with a thickness of 0.1 mm and a purity of 99.8%,
Chemical etching was performed by immersing it in a 2.5 wt% hydrochloric acid solution at a temperature of 60°C. The aluminum foil base material after etching had microscopic irregularities with an average surface roughness of 0.5 μm or less formed on the surface, and a large number of etching pores with a depth of about 10 μm and an inner diameter of about 20 μm. . Moreover, the surface magnification of the base material was about 30 times. Next, a titanium vapor-deposited film having a maximum thickness of 1.0 μm was formed on the surface of the etching foil base material by vacuum vapor deposition. The surface of this film had a morphology in which fine particles with an average outer diameter of 0.5 μm were deposited. In the case of this example, almost no titanium vapor-deposited film was formed on the inner surface of the pore. Example 2 Aluminum foil with a thickness of 0.1 mm and a purity of 99.8%,
Immersed in 3.0wt% hydrochloric acid solution at 65℃, 20A/
AC electrolytic etching was performed for 300 seconds at a current density of 50 cm ² . On the surface of the aluminum foil base material after etching, microscopic irregularities with an average size of 0.5 μm or less were formed, and many etching pores with a depth of about 20 μm and an inner diameter of about 30 μm were formed. Moreover, the surface magnification of the base material was about 50 times. Next, titanium was evaporated onto the surface of the etching foil base material in an argon gas atmosphere of 5×10 ^-3 Torr to a maximum depth of 0.5 μm.
A titanium vapor-deposited film was formed. The surface of this film had spherical protrusions formed by a large number of titanium fine particles having an average outer diameter of 0.6 μm. In this example, a titanium vapor-deposited film was also formed on a part of the inner surface of the etching pore. Comparative example: Using a smooth aluminum foil with a thickness of 0.1 mm and a purity of 99.8% as a base material, 5×
Titanium was evaporated in an argon gas atmosphere of 10 ^-3 Torr to form a titanium vapor deposited film with a thickness of 0.7 μm. The surface of this film had spherical protrusions formed by a large number of titanium fine particles having an average outer diameter of 0.2 μm. The titanium vapor-deposited films in Examples 1 and 2 and Comparative Examples were formed at an evaporation distance of 250 mm between the evaporation source and the substrate, and a evaporation rate of 200 A°/sec. The capacitance of the three types of cathode materials prepared as described above was measured at 30°C in a 10 wt% ammonium borate solution. The results are shown in the table.

[Table] As is clear from the above results, it was confirmed that the cathode material according to the present invention has a significantly better capacitance than the conventional cathode material in which the base material is not roughened. .

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of the surface portion of the cathode material for an electrolytic capacitor according to the present invention, and FIG.
Figures A, B, and C are schematic cross-sectional views showing typical examples of the form of pores formed on the surface of the base material. 1... Base material, 2... Titanium vapor deposited film, 3... Fine irregularities, 4... Pores.

Claims (1)

[Claims] 1. Pores with a maximum depth of 25 μm or less and a maximum internal diameter of 100 μm or less are distributed in the surface of a finely roughened aluminum foil base material at a density of 100 pores/cm ² or more. A cathode material for an electrolytic capacitor, characterized in that at least a surface portion of the base material excluding the pores is coated with a titanium vapor-deposited film. 2 The titanium vapor deposited film has an average particle size of 0.01 to 1.0 μm.
The cathode material for an electrolytic capacitor according to claim 1, which is a film having a thickness of 0.05 to 5.0 μm and made of fine titanium particles.