JPH03196510A - Electrode foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To increase capacitance by forming an aluminum deposited film onto a base body and forming a film composed of at least one element selected from the group of titanium, zirconium, tantalum, niobium and hafnium onto the aluminum deposited film. CONSTITUTION:An aluminum deposited film is formed onto a least one surface of a base body, and a film consisting of at least one element selected from the group of titanium, zirconium, tantalum, niobium and hafnium is formed onto the aluminum deposited film. An aluminum foil, metallic foils except aluminum, a plastic film, paper, etc., can also be used besides an aluminum foil as the base body, but it is favorable that the aluminum foil, the aluminum alloy foil or plastic film is adopted from the point of view of small leakage currents and high mechanical strength. Accordingly, much effect on the miniaturization and the increase of capacity of an electrolytic capacitor is brought about.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electrode foil for electrolytic capacitors.

More specifically, the present invention relates to an electrode material that contributes to increasing the size and capacity of electrolytic capacitors.

[Prior Art] As an electrode material for electrolytic capacitors, aluminum foil that is generally etched to enlarge its surface area is used. Increasing the surface area of the electrode is essential for increasing the capacitance of a capacitor, and the demand for smaller size and larger capacity demands further expansion of the surface area of the electrode.

However, increasing the surface area of aluminum foil by etching is approaching its limit due to factors such as a decrease in the strength of the aluminum foil.

On the other hand, in JP-A-59-167009,
Forming a porous film by depositing conductive metals such as aluminum, tantalum, titanium, niobium, and zirconium on a substrate such as aluminum foil in an inert gas to expand the surface area of the electrode and increase the dielectric constant. is proposed.

These conductive metals, except for aluminum, are high melting point materials, and large amounts of power must be applied to evaporate them, which may damage the flatness of the substrate due to heat damage, or cause the evaporation process to increase due to the temperature rise of the substrate. There is a problem that the film becomes smooth and the desired surface area expansion effect cannot be obtained. On the other hand, since aluminum has a low melting point of 660°C, damage to the substrate due to thermal damage is less likely to occur, but since the dielectric constant is the same as that of conventional electrolytic capacitor electrode foil, it is less effective in making capacitors smaller and larger in capacity. There is.

In order to suppress thermal damage during evaporation, the titanium film thickness for each evaporation film was made thinner, and evaporation was repeated intermittently.
It was disclosed in Japanese Patent Application Laid-Open No. 1988-63 that a titanium film with a predetermined thickness can be formed by this method.
This is proposed in the publication No.-255910.

However, repeating vapor deposition intermittently to form a titanium film of a predetermined thickness is not only undesirable from the viewpoint of productivity, but also causes the formation of a natural oxide film at the interface of the intermittently deposited titanium film, resulting in the formation of a titanium film on the outermost layer. There is a risk that the capacitance will become a series capacitor with respect to the oxide film of the capacitor, inhibiting the increase in capacitance.

[Problems to be Solved by the Invention] The present invention was devised in view of the above-mentioned drawbacks of the prior art. An object of the present invention is to provide an electrode foil material for electrolytic capacitors that is free from damage and productivity reduction.

[Means to solve the problem] The object of the present invention is achieved by the following configuration.

(1) An aluminum vapor deposited film is formed on at least one side of the substrate, and at least one film selected from the group of titanium, zirconium, tantalum, niobium, and hafnium is formed on the aluminum vapor deposited film. Electrode foil for electrolytic capacitors.

(2) Titanium, zirconium, or
An alloy film made of aluminum and at least one metal selected from the group of tantalum, niobium, and hafnium is formed, and the alloy film is mainly composed of aluminum on the interface side with the substrate and on the surface side of the alloy film. Titanium,
An electrode foil for an electrolytic capacitor, which is mainly composed of a metal selected from the group of zirconium, tantalum, niobium, and hafnium, and whose composition changes continuously in the film thickness direction.

In addition to aluminum foil, aluminum alloy foil, metal foil other than aluminum, plastic film, paper, etc. can be used as the substrate of the present invention, but aluminum ,
Preferably, aluminum alloy foil or plastic film is used. It is preferable for these metal foils to be roughened by etching or sandblasting to increase the surface area, but to increase productivity by omitting processes, it is preferable to leave them flat in the manufactured state. It is preferable that there be. The thickness of the metal foil is preferably in the range of 10 to 100 μm in view of the relationship between mechanical strength and occupied volume.

Plastics for the plastic film include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, polyethers such as polyphenylene sulfide, aromatic polyamides, polycarbonates, polyether ketones, etc. Polyethylene terephthalate or polyprolylene is preferred from the viewpoint of cost. In terms of mechanical stability and strength, these plastics are preferably biaxially stretched to form a film. The thickness of the plastic film is determined from the relationship between mechanical strength and occupied volume.
A range of 50 μm is preferred.

When the aluminum vapor-deposited film and at least one film selected from the group of titanium, zirconium, tantalum, niobium and hafnium are formed on only one side of a non-conductive substrate such as a plastic film, these films are formed. Preferably, the side opposite to the one to which the metallization is applied is metallized. In this case, the plastic film can be metallized by forming a metal film by vapor deposition or sputtering. The metal film is preferably an aluminum film or a zinc film because the higher the conductivity, the smaller the dielectric loss. The thickness of the metal film is preferably in the range of 0.03 to 0.15 μm, since the thicker the metal film, the better the conductivity, and the thinner the metal film, the easier it is to self-heal. The plastic film may be subjected to pre-treatment such as adhesion-facilitating treatment prior to metallization.

The aluminum vapor deposited film formed on at least one side of the substrate has a purity of 99.9% or more, preferably 99.9% or more.
A value of 9% or more is desirable in that the capacitance can be increased. The thickness of the aluminum film should be from 0.1 to 0.1, since the thicker the aluminum film, the greater the capacitance.On the other hand, if it is too thick, it will impair the flexibility of the base and will not increase the capacitance commensurate with the cost. The range is preferably 10 μm, more preferably 0.2 to 5 μm.

The aluminum deposited film is preferably porous in order to increase capacitance. In order to form a porous film, a known oblique evaporation method or an inert gas evaporation method can be used. That is, the oblique vapor deposition method is a method of forming a thin film by making a metal vapor flow obliquely incident on a substrate running along a flat plate or cylindrical substrate support from the perpendicular direction. The angle of incidence of the vapor flow on the substrate is approximately constant when the substrate support is a flat plate, and varies continuously when the substrate support is cylindrical.

In addition, the inert gas vapor deposition method introduces an inert gas such as argon, helium, or neon into the vapor deposition tank, and performs vapor deposition at an atmospheric pressure of 10-' to 10-2 Torr to form a porous thin film. This is a method of forming. Titanium, zirconium, tantalum,
At least one film selected from the group of niobium and hafnium is laminated. The purity of these membranes is 99.8% or more, more preferably 99.8% or more in order to reduce leakage current.
It is desirable that it is 9% or more. In order to suppress thermal damage to the substrate and to reduce costs, it is better to make these films thinner.On the other hand, in order to increase capacitance, it is better to have a thicker film. It is preferably selected from the range of .03 to 1 μm, and more preferably selected from the range of 0.05 to 0.5 μm.

At least one film selected from the group consisting of titanium, zirconium, tantalum, niobium, and )1 hn to be laminated on the aluminum film of the present invention is porous in order to increase the capacitance, similar to the aluminum film. It is preferable that there be. In order to form a porous film, the known oblique evaporation method or inert gas evaporation method can be used as in the case of the aluminum film.

Titanium is preferred as the metal used to form the film laminated on the aluminum vapor-deposited film of the present invention because it has a high dielectric constant, a low melting point, and is relatively inexpensive.

Another aspect of the present invention is that titanium is used on at least one side of the substrate.
An alloy film made of aluminum and at least one metal selected from the group of zirconium, tantalum, niobium, and hafnium is formed, and the alloy film is mainly made of aluminum on the interface side with the substrate, and The surface side is mainly made of a metal selected from the group of titanium, zirconium, tantalum, niobium, and hafnium, and the composition changes continuously in the film thickness direction. An example of an alloy film provided on a substrate will be explained using FIG. 1.

Figure 1 shows the composition change in the film thickness direction of an alloy film made of aluminum and titanium among the alloy films of the present invention. This was measured by X-ray microanalysis while observing the cross-sectional structure of. The right side of the horizontal axis is the substrate side, and the left side is the surface side of the alloy film. The substrate is aluminum foil.

The alloy film is mainly made of aluminum on the base side, and the surface of the alloy film is mainly made of titanium. Further, inside the alloy film, the composition changes continuously in the film thickness direction.

A material whose composition changes continuously in the film thickness direction is called a gradient material, and the gradient material of the present invention has the following advantages.

That is, in the gradient material of the present invention, as illustrated in FIG. 1, the aluminum vapor deposited film and the titanium film partially overlap in time and space, so there is no interface.
Therefore, there is no possibility that a natural oxide film will be formed at the interface between the aluminum vapor deposited film and the titanium film. Further, since there is no interface between the aluminum vapor deposited film and the titanium film, there is no fear that the titanium film will peel off from the aluminum vapor deposited film. Furthermore, when sequentially laminating an aluminum vapor-deposited film and a titanium film, two separate vapor deposition processes are required, or one evaporation source and two vapor deposition chambers must be prepared. Since the gradient material of the invention can be produced in one vapor deposition chamber using one dual evaporation source, it is very superior in terms of simplifying the manufacturing equipment and improving productivity.

It is better for the alloy film of the present invention to be thin in order to suppress thermal damage to the substrate and to reduce costs, and on the other hand, it is better to have a thick film in order to increase capacitance.
It is preferably selected from the range of 1 to 10 μm, and 0
．． More preferably, the thickness is selected from the range of 2 to 5 μm. In the composition distribution in the film thickness direction of the alloy film, a point where the ratio of aluminum and at least one metal selected from the group of titanium, zirconium, tantalum, niobium and hafnium is reversed (point A in Figure 1) It is better to place it at a shallow position from the surface of the alloy film in order to suppress thermal damage to the substrate and to reduce costs (on the other hand, in order to increase the capacitance, it is better to place it at a shallow position from the surface of the alloy film). Since the deeper the better, the position of point A in Figure 1 is shallower than 1/2 of the thickness of the alloy film (and preferably deeper than 1/50, and 1/3 of the thickness of the alloy film from the surface of the alloy film). shallower and 1/30th
It is even more preferable that it be located at a deeper position.

An example of the method for manufacturing the electrode foil for electrolytic capacitors of the present invention is shown below, but the method is not limited thereto.

FIG. 2 is a schematic diagram of a vacuum evaporation apparatus equipped with a long substrate traveling system. A long substrate traveling system consisting of an unwinding shaft 2, a cylindrical cooling drum 3, and a winding shaft 4 is installed in a vacuum chamber 1. An aluminum foil base 5 of a predetermined thickness is attached to the base traveling system.
Set up. The vacuum chamber 1 is separated by partition walls 7 and 8 into an upper chamber 15 in which an unwinding shaft and a winding shaft are housed, and a lower chamber 16 in which an evaporation source 6 is housed. Exhausted. Apply 5X10-'Tor to the inside of the lower tank.
The lower tank hair argon gas is supplied through the valve 11, and the pressure is set to lXl0-'~1x1O-2 Torr.
Adjust to a predetermined pressure in the range of r.

The evaporation source is an electron beam heater equipped with two crucibles.
An aluminum ingot 12 and a titanium ingot 13 are filled respectively. The aluminum ingot is melted and evaporated while the base body is running to form an aluminum vapor deposited film of a predetermined thickness on the aluminum foil.

Next, after adjusting the amount of argon gas to bring the pressure inside the tank to a predetermined value, the traveling direction is reversed and the substrate is made to travel, while the titanium ingot is melted and evaporated to form a predetermined thickness on the aluminum vapor deposited film. laminate titanium films. In this way, an electrode foil for an electrolytic capacitor in which an aluminum vapor-deposited film and a titanium film are laminated on an aluminum foil substrate is obtained.

An alloy film made of aluminum and at least one metal selected from the group of titanium, zirconium, tantalum, niobium and hafnium is formed on at least one side of the base of the present invention, and the alloy film is on the interface side with the base. An electrolytic capacitor whose composition changes continuously in the film thickness direction is mainly made of aluminum, and the surface side of the alloy film is mainly made of a metal selected from the group of titanium, zirconium, tantalum, niobium, and hafnium. An example of the method for manufacturing the electrode foil is shown below, but the method is not limited thereto.

A vacuum evaporation apparatus equipped with a long substrate traveling system shown in FIG. 2 is used. An aluminum foil substrate 5 having a predetermined thickness is installed on the substrate traveling system. Exhaust the inside of the vacuum chamber from exhaust ports 9 and 10,
The inside of the lower tank is evacuated to below 5X10-' Torr. Supply the lower tank hair gas through the valve 11 and increase the pressure to 1X.
The pressure is adjusted to a predetermined pressure in the range of 10-' to 1×IQ-2 Torr. The evaporation source is an electron beam heater equipped with two crucibles, and the crucible on the upstream side in the direction of substrate travel is filled with aluminum ingot 12, and the crucible on the downstream side in the direction of substrate movement is filled with titanium ingot 13. An aluminum ingot and a titanium ingot are melted and evaporated while the base body is running to form an alloy film of aluminum and titanium with a predetermined thickness on the aluminum foil. By filling the crucible with an aluminum ingot on the upstream side of the substrate running direction and filling the titanium ingot on the downstream side of the substrate running direction, a film that is mainly aluminum at the interface with the substrate and titanium at the surface is continuous in the thickness direction. It is possible to obtain an alloy film whose composition changes dramatically. The composition distribution in the film thickness direction of the alloy film can be controlled by adjusting the electron beam power applied to the aluminum ingot and titanium ingot or by the position of the crucible. In order to obtain the alloy film of the present invention in which the composition changes continuously in the film thickness direction, the two crucibles containing ingots 12 and 13 should be placed in the direction of substrate travel as much as possible within the range that reduces the deposition rate. It is desirable that they be installed at a distance from each other. It is also preferable to install a shielding plate 14 between the two crucibles because it is effective in obtaining the alloy film of the present invention whose composition changes continuously in the film thickness direction.

Although induction heaters, resistance heaters, laser heaters, etc. can be used as evaporation sources for aluminum, titanium, zirconium, tantalum, niobium, and hafnium, electron beam heaters are used to evaporate high-melting point metals at high speed. It is preferable to do so.

It is permissible to perform ion blating by emitting high frequency power between these evaporation sources and the substrate as appropriate.

[Effects of the Invention] The present invention provides an electrolytic method in which an aluminum vapor deposited film is formed on at least one side of a substrate, and at least one film selected from the group of titanium, zirconium, tantalum, niobium, and hafnium is further formed on the aluminum vapor deposited film. This is electrode foil for capacitors. Aluminum, a low dielectric constant but low melting point material, is formed relatively thickly to create a roughened surface, followed by high dielectric constant but high melting point materials such as titanium, zirconium, tantalum, niobium and By laminating at least one material selected from the group of hafnium in a relatively thin layer, the aim is to obtain a surface with a high dielectric constant and a large area, with good productivity and without causing thermal damage to the substrate. The capacitance per unit area can be increased, and this has had a great effect on making electrolytic capacitors smaller and larger in capacity.

Another aspect of the present invention is to form an alloy film made of aluminum and at least one metal selected from the group of titanium, zirconium, tantalum, niobium, and hafnium on at least one side of the substrate, and the alloy film is made of aluminum. At the interface with the substrate, aluminum is the main component, and on the surface of the alloy film, the main component is a metal selected from the group of titanium, zirconium, tantalum, niobium, and hafnium.The composition changes continuously in the film thickness direction. Since this is an electrode foil for electrolytic capacitors, it is possible to increase the capacitance per unit area without causing heat damage to the substrate. Since it is formed as a metal layer, there is no interface, so there is no risk of peeling or oxidation of the interface.It is also highly effective in simplifying manufacturing equipment and improving productivity.

[Method for Measuring and Evaluating Characteristics] (1) Method for Measuring Capacitance Cut a sample into a size of 50 mm x 50 mm and attach it to a holder so that only the surface to be measured is exposed. A sample holder and a carbon plate were opposed to each other at an interval of 50 mm using a 10% by weight aqueous ammonium borate solution as an electrolyte. The capacitance was measured using an LCR meter using the sample and the carbon plate as electrodes. The measured value was divided by 25 (cm2) to obtain the capacitance per unit area.

(2) Method for measuring film thickness and composition distribution in the depth direction In order to observe the cross-sectional structure, the sample is processed into ultra-thin sections using a microtome. The ultra-thin section is observed with a transmission electron microscope (New Model H-600 manufactured by Hitachi Seisakusho) and the film thickness is read. The composition distribution in the depth direction was determined by observing the ultrathin section with a transmission electron microscope.
It is obtained by measuring with X-ray microanalysis (XMA).

In addition, Auger electron spectroscopy or a combination of secondary ion mass spectrometry and ion etching can also be employed as a method for measuring the film thickness and composition distribution in the depth direction.

[Examples] The present invention will be specifically described below with reference to Examples, but the present invention is not limited thereto.

Example 1 A vacuum evaporation apparatus equipped with a long substrate transport system shown in FIG.
A 0 μm long aluminum foil substrate was attached. After filling an electron beam heater 6 equipped with two evaporation source crucibles with an aluminum ingot 12 and a titanium ingot 13, the inside of the vacuum chamber 1 is evacuated through exhaust ports 9 and 10, and the partition walls 7 and 8 are closed. The pressure inside the lower tank 16 was reduced to 5×IQ-5 Torr or less. Next, the lower tank hair gas is supplied through the valve 11, and the pressure inside the lower tank is increased to 8X1.
It was adjusted to 0-'Torr. While the substrate was running, the aluminum ingot was melted and evaporated to form an aluminum vapor deposited film with a thickness of 0.5 μm on the aluminum foil at a deposition rate of 10 μm/min.

Next, adjust the argon gas amount to increase the pressure inside the lower tank to 6×10
-' I set it to Torr. A long aluminum foil substrate is run with the running direction reversed, and a titanium ingot is melted and evaporated onto the aluminum deposited film at a deposition rate of 4 μm/min to a thickness of 0.5 μm. A 1 μm titanium film was laminated. Note that when forming the aluminum vapor deposited film and the titanium film, the cooling drum 3 was cooled to -20°C.

The thus obtained electrode foil for an electrolytic capacitor showed almost no deformation due to heat and had good flatness.

When the capacitance of the electrolytic capacitor electrode foil was measured using a 10% aqueous ammonium borate solution as the electrolyte, it was found to be 38μ.
A large value of F/cm2 was obtained.

In the case of only the aluminum foil, the capacitance is 3 μF/cm
It was 2.

Example 2 A vacuum evaporation apparatus equipped with a long substrate transport system shown in FIG.
A 0 μm long aluminum foil substrate was attached. After filling the crucible on the upstream side in the substrate running direction with the aluminum ingot 12 and the titanium ingot 13 in the crucible on the downstream side in the substrate running direction in the electron beam heater 6 equipped with two crucibles as evaporation sources, the inside of the vacuum chamber 1 is evacuated. The pressure inside the lower tank 16 separated by the partition walls 7 and 8 was reduced to 5xlO-'Torr or less by evacuating through the ports 9 and 10. Next, valve 11
The lower tank hair gas is supplied through the lower tank, and the pressure inside the lower tank is increased to 6.
It was adjusted to X10-4 Torr. An aluminum ingot and a titanium ingot were simultaneously melted and evaporated while the substrate was running to form an alloy film of aluminum and titanium with a thickness of 0.6 μm on the aluminum foil at a deposition rate of 10 μm/min.

The thus obtained electrode foil for an electrolytic capacitor showed almost no deformation due to heat and had good flatness.

The composition distribution of the alloy film in the film thickness direction was measured using a transmission electron microscope and It was at a depth of .1 μm.

When the capacitance of the electrolytic capacitor electrode foil was measured using a 10% aqueous ammonium borate solution as the electrolyte, it was found to be 30μ.
A large value of F/cm2 was obtained.

Comparative Example 1 A long aluminum foil substrate having a thickness of 20 μm was attached to the vacuum evaporation apparatus shown in FIG. After filling only the titanium ingot into the electron beam heater 6, the inside of the vacuum chamber 1 is evacuated through the exhaust ports 9 and 10, and the pressure inside the lower chamber 16 separated by the partition walls 7 and 8 is increased to 5X 10-5 Torr. I made it below. Next, hair argon gas was supplied to the lower tank through valve 1, and the pressure inside the lower tank was adjusted to 6×10 Torr. A titanium ingot was melted and evaporated while the substrate was running, and a thickness of 0 was deposited onto the aluminum foil at a deposition rate of 4 μm/min.
A 66 μm titanium film was laminated.

The thus obtained electrode foil for an electrolytic capacitor was significantly deformed due to thermal expansion during vapor deposition, and it was difficult to wind it into a member in the shape of a capacitor.

Comparative Example 2 A long aluminum foil substrate with a thickness of 20 μm was attached to the vacuum evaporation apparatus shown in FIG. After filling only the aluminum ingot into the electron beam heater 6, the inside of the vacuum chamber 1 was evacuated, and the pressure inside the lower chamber 16 separated by the partition walls 7 and 8 was reduced to 5×10 −′ Torr or less. Next, the lower tank hair gas is supplied through the valve 11, and the pressure inside the lower tank is increased to 8X1.
．． It was adjusted to O-'Torr. The aluminum ingot was melted and evaporated while the substrate was running, and an aluminum vapor deposited film with a thickness of 0.6 μm was laminated on the aluminum foil at a deposition rate of 10 μm/min.

The thus obtained electrode foil for an electrolytic capacitor was hardly deformed by heat during vapor deposition and had good flatness.

However, when the capacitance of the electrode foil for an electrolytic capacitor was measured using a 10% aqueous ammonium borate solution as an electrolyte, it was 10 μF/cm 2 and the increase in capacitance was small.

Comparative Example 3 A long aluminum foil substrate with a thickness of 20 μm was attached to the vacuum evaporation apparatus shown in FIG. After filling only the titanium ingot into the electron beam heater 6, the inside of the vacuum chamber 1 was evacuated through the exhaust ports 9 and 10, and the pressure inside the lower chamber 16 separated by the partition walls 7 and 8 was reduced to 5×10'Torr or less. . Next, hair argon gas was supplied to the lower tank through the valve 11, and the pressure inside the lower tank was adjusted to 6×10 −′ Torr. A titanium ingot was melted and evaporated while the substrate was running, and a thickness of 0.1 μm was deposited onto the aluminum foil at a deposition rate of 4 μm/min.
titanium films were laminated.

The thus obtained electrode foil for electrolytic capacitors showed slight deformation due to heat and relatively good flatness, but the capacitance was 15
The effect of increasing μF/Cm2 and capacitance was small.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a compositional change in the film thickness direction of an alloy film constituting the electrode foil of the present invention. FIG. 2 shows an example of a vacuum evaporation apparatus for manufacturing the electrode foil for electrolytic capacitors of the present invention, in which 5 is a substrate, 6 is an evaporation source, 11 is a gas supply valve, and 12 and 13 are evaporation materials. .

Claims (2)

[Claims] (1) An aluminum vapor deposited film is formed on at least one side of the substrate, and at least one film selected from the group of titanium, zirconium, tantalum, niobium, and hafnium is formed on the aluminum vapor deposited film. Electrode foil for electrolytic capacitors. (2) Titanium, zirconium, or
An alloy film made of aluminum and at least one metal selected from the group of tantalum, niobium, and hafnium is formed, and the alloy film is mainly made of aluminum on the interface side with the substrate and titanium on the surface side of the alloy film. ,
An electrode foil for an electrolytic capacitor, which is mainly composed of a metal selected from the group of zirconium, tantalum, niobium, and hafnium, and whose composition changes continuously in the film thickness direction.