JPH07109036B2 - Aluminum electrode material for electrolytic capacitors - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum electrode material for electrolytic capacitors.

2. Description of the Related Art Aluminum foil used as an aluminum electrode material for electrolytic capacitors is required to have a surface area as large as possible and a large capacitance per unit volume. For this reason, it is generally performed to increase the effective surface area of the aluminum foil by subjecting it to electrochemical or chemical etching treatment. Furthermore, in order to increase the surface expansion rate as much as possible, etching holes are formed. Material improvements, more etch methods, more, deeper and thicker,
Various researches have been made such as improvement on the manufacturing process of foil.

As an improvement from the aspect of the electrode material, conventionally, in addition to improving the alloy composition such as adding a trace amount of a noble metal that is more than aluminum, which is an etching nucleus, to the aluminum foil, an alloy structure such as adjusting the crystal orientation to 100 Various methods have been proposed, including further improvement by surface treatment such as forming a thin film layer containing a metal nobler than aluminum that forms etching nuclei on the foil surface.

The problem to be solved by the invention is that, in practice, even in the case of using the improved aluminum electrode material as described above, in the conventionally known etching technique, the generation site of the etching hole is generally non-uniform. In addition, the etching holes that try to increase the number of etching holes communicate with each other and become coarse holes, and the melting of the aluminum foil surface progresses at the same time to impair the mechanical strength of the foil, and the etching holes are deep. However, there is a problem that it is difficult to obtain the effect of increasing the surface expansion ratio, which is sufficiently described in the result, due to the drawback that it does not work. In particular, regarding the nonuniformity of the site where the etching holes are generated, since nonuniform etching pits are generated during etching due to segregation of impurity atoms contained in the aluminum foil, intermetallic compounds, the presence of grain boundaries, etc. It was difficult to avoid.

The present invention solves such a problem and enables the aluminum foil to have a required mechanical strength and uniformly form a large number of deep etching holes, and has an excellent surface expansion ratio, that is, electrostatic capacitance. The purpose of the invention is to obtain an aluminum electrode material for an electrolytic capacitor which can be manufactured.

Means for Solving the Problems In the above object, one of the inventions is to perform halftone dot printing on a surface of an aluminum foil (1) by using a metal ink containing a metal powder that is more noble than aluminum. The present invention provides an aluminum electrode material for electrolytic capacitors, characterized in that a large number of halftone dot portions (2) having an ink etching promoting coating (3) are formed in a high density arrangement. In addition to the above, the entire other surface portion excluding the halftone dot portion is subjected to halftone dot printing using a resist ink, thereby forming a resistant film of the resist ink. Provided is an aluminum electrode material for an electrolytic capacitor, which enables etching regardless of the presence of intermetallic compounds, grain boundaries, etc. in the aluminum foil material. To obtain an electrode material capable of forming a large number of deep etching holes uniformly by preliminarily determining the site where holes are formed and enabling the limited and preferential erosion of fine halftone dots of the aluminum foil during the etching process. It was successful.

The metal ink for forming the etching-promoting film (3) on the halftone dot portion (2) uses, for example, a resin such as a modified phenol resin as a binder, and a metal that is more noble than the potential of aluminum, such as Pb, Bi, Cu, One, two or more kinds of metal powders such as In, Sn, Ag, and Ti are added and contained, and the content of the metal powders is about 1 to 80 wt%, particularly preferably 10 to 50 wt%. And The halftone dot portion (2) having the etching promoting film (3) controls the formation site and density of etching nuclei during etching, and directly affects the final capacitance and mechanical strength of the aluminum foil electrode material. Since it has an influence, its arrangement and size are determined in consideration of the required capacitance. The shape of the halftone dot portion is not particularly limited, but is generally circular, and its diameter (l) is in the range of 1 to 5 μm,
Moreover, the arrangement pitch also defines the interval (d) between the halftone dots as 1
It is preferable to have a high density distribution in the range of ˜5 μm. Particularly preferably, the diameter is 1 to 2 μm and the interval is about 1 to 2 μm.

The halftone dot portion (2) is formed by a halftone dot printing technique using, for example, a plate having a large number of halftone dots, such as a PS plate.

As the aluminum foil (1), one made of high-purity aluminum having a purity of 99.9 wt% or more is used, as is conventionally used as a high voltage anode material. The surface roughness of the aluminum foil also affects the capacitance. That is, the use of an aluminum foil having a smooth surface as much as possible is recommended from the viewpoint of increasing the capacitance,
It is preferable to use an aluminum foil having a smooth mirror surface of Rmax × 0.1 μm or less.

When the aluminum electrode material according to the present invention described above is etched according to the conventional method, the generation of etching nuclei is promoted in the halftone dot portion having the etching promoting film, and the halftone dot portion is eroded intensively. As a result, uniform and deep etching holes are formed. The surface roughness of the aluminum foil is preferably as small as possible to obtain good results because the formation of the above-mentioned etching nuclei is prevented from unnecessarily occurring in the portion other than the halftone dot portion, and the entire surface dissolution is prevented. Based on what can be suppressed.

In order to more reliably prevent the formation of the etching holes (5) in the area other than the halftone dot portion (2) of the aluminum foil and to suppress the surface dissolution, additional halftone dot printing is performed using a resist ink. , The halftone dot part (2) as shown in FIG.
By forming a resistant film (4) made of the above resist ink on the entire other part except for
Further good results can be obtained. The resist ink may be any one as long as it has resistance to an acid or an alkali etching solution at the time of etching treatment, and for example, a hydrochloric acid-resistant alkali-removable acrylic resin or other resist agent for semiconductor photomask can be used. .

In use, the above electrode material according to the present invention is electrochemically or chemically etched in an acid or alkaline bath to be finished into an aluminum electrode foil. Prior to such etching, dry etching may be performed in order to make initial unevenness on the surface of the electrode material. The etching solution used in the etching treatment is not particularly limited, and a known 2 to 15% hydrochloric acid aqueous solution, or an aqueous solution in which an acid such as chromic acid, sulfuric acid, or oxalic acid is further added to the solution is arbitrarily selected. Adopted Can be used. Other etching treatment conditions, that is, the liquid temperature, the current density, the etching time, etc. may be the same as the conventionally known etching treatment conditions. This etching treatment promotes the generation of etching nuclei in the halftone dot portion (2) of the aluminum foil due to the action of the etching-promoting film (3) due to the metal ink present there, and the erosion proceeds intensively in the portion. ,
It enables the formation of deep and thick etching holes (5). In the electrode material in which the resist film (4) made of the resist ink is formed on the portion other than the halftone dot portion (2), the surface dissolution of the portion other than the halftone dot portion is more surely prevented. It enables formation and prevents the mechanical strength of the foil from decreasing.

In addition, in the case of an electrode material having a resistant coating (4), after the etching treatment is finished, the resistant coating adhered to the foil surface is removed by immersing the electrode material in an alkaline solution such as a few% NaOH solution. Processing is performed.

EFFECTS OF THE INVENTION As described above, the electrode material according to the present invention has a large number of halftone dot portions having an etching promoting film formed by an ink containing a metal nobler than aluminum on the surface of the aluminum foil by high density distribution. Therefore, during the subsequent etching treatment of the electrode material, the area where the etching nuclei are generated is limited to the above-mentioned halftone dot area, and this area is intensively attacked, resulting in the complete surface dissolution. It is possible to form deep and thick etching holes while suppressing the above.

Further, in the electrode material of the present invention, unlike the conventional electrode material, variations in material characteristics such as intermetallic compounds and uneven distribution of crystal grain boundaries do not directly affect the etching characteristics. Therefore, it is possible to provide a stable electrode material with less variation.

Further, by selecting the halftone dot printing pattern, the capacitance to be obtained can be freely controlled, the electrode material can be easily designed according to the capacitance to be obtained, and the electrode material is not wasted during etching. Since the surface is not melted, the electricity consumption required for etching can be reduced.

Furthermore, the electrode foil of the present invention forms a halftone dot portion having an etching promoting film on the surface by a halftone dot printing technique,
Furthermore, since a resistant coating is formed on the portion excluding the portion, it is easier to treat a large area aluminum foil as compared with the case where a porous resistant coating is formed by a patterning method using a photoresist, and continuous treatment is possible. Therefore, a large area can be obtained at low cost.

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

Metal ink containing 20wt% of each metal powder consisting of Pb, Bi and Cu in modified phenol resin on the surface of each annealed aluminum foil with thickness 100μm, purity 99.99%, surface roughness Rmax x 0.02μm or less. Was used to perform halftone dot printing with a PS plate, thereby forming a large number of halftone dot portions having an etching-promoting film made of the above ink in a high-density distribution. Various electrode materials of Sample Nos. 1 to 4 were obtained by varying the halftone dot portion within a range of a diameter of 1.5 to 4.0 [mu] m and an interval of 1.5 to 3.0 [mu] m.

In addition, for sample No. 5, the surface of the foil other than the above halftone dots was subjected to anodizing treatment at a current density of 1 A / dm ² × 1 minute in a 5% H ₂ SO ₄ aqueous solution at 30 ° C. It is assumed that a resistant coating made of an anodized film is formed on the entire part, and that for sample No. 6, the same resistant coating made of a chromate film is formed by subjecting it to chromate treatment by a conventional method, Further, Sample No. 7 was subjected to a heat oxidation treatment at 250 ° C. for 2 hours in the atmosphere to form the same resistant film made of an oxide film.

Then, to the above various aluminum electrode materials according to the present invention,
Electrolytic etching was performed under the conditions of etching solution: 5 wt% hydrochloric acid aqueous solution, temperature: 75 ° C., direct current density: 10 A / dm ² , etching time: 7 minutes.

Thereafter, Sample Nos. 5 to 7 were immersed in 5 wt% sodium hydroxide at 25 ° C. for 2 seconds to remove the resistant coating.

The various etching foils obtained above were 380 V in a boric acid bath.
After chemical conversion, the capacitance of the foil was measured. On the other hand, this result was compared with that of an aluminum foil (comparative example) in which the same aluminum material as that described above was used and the surface was not treated under the same etching conditions and only etching was performed. The comparison of the electrostatic capacities was evaluated by the relative ratio when the electrostatic capacity of the comparative example was 100. The results are shown in the table below.

As shown in the results of the above table, the electrode material according to the present invention is
It was possible to obtain a remarkable effect of increasing the electrostatic capacitance as compared with the comparison with the conventional product.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of an arrangement state of halftone dots by halftone printing, and FIG. 2 is a schematic sectional view of the same. (1) …… Aluminum foil, (2) …… Halftone dots,
(3) ... Etching promoting film, (4) ... Resistive film.

Claims (7)

[Claims] 1. A large number of halftone dots having an etching accelerating film (3) formed by the ink by performing halftone dot printing on the surface of an aluminum foil (1) using a metal ink containing a metal powder nobler than aluminum. An aluminum electrode material for electrolytic capacitors, characterized in that part (2) is formed in a high-density arrangement. 2. The halftone dot portion (2) is circular and has a size in the range of 1 to 5 μm in diameter, and its interval is also 1 to 5.
The aluminum electrode material for an electrolytic capacitor according to claim 1, wherein the aluminum electrode material has a range of μm. 3. The aluminum electrode material for an electrolytic capacitor according to claim 1, wherein the aluminum foil (1) is made of high density aluminum having a purity of 99.9% or more. 4. A large number of halftone dot portions (3) having an etching accelerating film (3) formed by printing the ink on the surface of an aluminum foil (1) using a metal ink containing a metal powder nobler than aluminum. 2) is formed in a high-density arrangement, and an aluminum electrode material for an electrolytic capacitor, characterized in that a resistant coating is formed by subjecting the entire surface part other than the halftone dot part to a surface treatment. . 5. The aluminum electrode material for an electrolytic capacitor according to claim 4, wherein the resistant coating is a chromate coating by chromate treatment. 6. The aluminum electrode material for an electrolytic capacitor according to claim 4, wherein the resistant film is an anodized film formed by anodizing treatment. 7. The aluminum electrode material for an electrolytic capacitor according to claim 4, wherein the resistant film is an oxide film formed by a heat oxidation treatment.