JP4002291B2 - Pit generation etching method - Google Patents

Description

  The present invention relates to a pit generation etching method capable of generating an etching pit by electroless etching an electrode foil for an aluminum electrolytic capacitor.

Aluminum anode foil is generally formed by forming tunnel-shaped holes called pits by etching the aluminum foil through an electrical or electrochemical electrolysis process, and etching it electrically or electrochemically or electrolessly. A processing step of enlarging the pit hole is performed. Usually, these processing steps are performed in two stages, as described above, an etching pit generation step and a pit expansion step that expands the generated pits to a thickness corresponding to the intended use. In the pit enlargement process, an electrolytic or chemical dissolution method is used.
This is because conventional foils have low solubility, and in the pit generation process, etching pits are not grown by chemical dissolution, so that electrolytic etching is indispensable.
Patent Document 1 proposes a technique that enables generation of pits in an electroless method by including various metal compounds in the pit generation process.
JP 2003-318069 A

By the way, normally, in the electrolytic etching in the actual machine line, a current of 3000 to 4000 A is applied, so that the foil generates heat. Therefore, it is difficult to exceed a certain amount of energization, and the electrolysis area is defined by the carbon electrode serving as a counter electrode, so that there has been a limit to improving the production capacity. Furthermore, the heat generation of the aluminum foil causes variations in the amount of energized electricity in the width direction, which contributes to variations in the capacitance of the etching foil.
In addition, since power is generally supplied using a copper tube roller, it causes sparking of the power supply section, which causes quality problems such as cutting of aluminum foil and hole defects. Furthermore, cooling equipment is required to prevent heat generation, leading to increased production equipment costs. As described above, when an electrolytic method is used in the pit generation process, it is difficult to reduce the cost of the etching foil.
From such a background, an electroless method as described in Patent Document 1 has also been proposed, but the method proposed in Patent Document 1 requires the use of a special reagent, and its management is also There are practical problems due to the complexity.

  On the other hand, the inventor of the present application has found that etching pits can be generated by an electroless method by containing a certain element in the aluminum foil without using a special reagent. Using this foil, etching pits can be generated easily and electrolessly without significantly changing the current production conditions. As a result, the production capacity can be expanded and the cost of manufacturing equipment can be reduced. A quality etching foil can be supplied.

  The present invention has been made against the background of the above circumstances, and provides an etching method capable of satisfactorily generating etching pits by an electroless method.

That is, the pit generation etching method of the present invention contains, by mass ratio, 20 to 200 ppm in total of one or more selected from Mn, Zn, Ni, Sn, Ag, Pt, and Au, and the balance. The surface layer portion including the oxide film on the surface of the aluminum alloy foil is brought into contact with the aluminum alloy foil after final annealing, which is made of Al and inevitable impurities, without contacting with a solution having a chlorine ion concentration of less than 1000 ppm. The surface layer is removed at a removal thickness of 200 mm, and then an etching pit generation process is performed without applying current or by applying a minute current of 100 mA / cm ² or less , and then an etching pit hole diameter expanding process is performed. It is characterized by that.

According to a second aspect of the present invention, in the pit generation etching method according to the first aspect , the pit diameter expanding step is performed by bringing a solution having a chlorine ion concentration of less than 1000 ppm into contact with the aluminum alloy foil.

According to a third aspect of the present invention, in the pit generation etching method according to the second aspect of the present invention, the surface layer portion removal and the etching pit hole diameter expanding step are performed using the same solution having a chlorine ion concentration of less than 1000 ppm.

The pit generation etching method according to claim 4 is the invention according to any one of claims 1 to 3 , wherein the etching pit generation step contacts the aluminum alloy foil with a solution containing 0.1 mol / l or more hydrochloric acid. It is characterized by being carried out.

That is, according to the present invention, an appropriate amount of the surface layer portion is removed by performing surface dissolution removal with a solution having a chlorine ion concentration of less than 1000 ppm. Removal of the surface layer portion shall be the 20～200A.
In order to enable generation and growth of etching pits by electroless, the present invention contains one or more selected from Mn, Zn, Ni, Sn, Ag, Pt, and Au. . Pit formation occurs because these elements and bulk aluminum cause a local cell reaction. In order to generate etching pits from the foil surface layer, it is necessary to contain an appropriate amount of these substances, specifically 20 to 200 ppm, and to concentrate on the aluminum foil surface by heat treatment. Usually, a foil having a cubic crystal ratio of 95% or higher is subjected to high-temperature annealing at 500 ° C. or higher, and therefore an oxide film having an average thickness of 20 to 60 mm is formed on the surface thereof. During this heat treatment, the substance that becomes the base point of the local battery reaction is concentrated on the aluminum foil inside the oxide film, so that the reactivity is low when the surface is thickly covered with the oxide film during the etching. The uniformity of pits is also poor. Then, the reactivity at the time of etching, etc. is improved by removing the surface layer part containing an oxide film by surface dissolution removal. Furthermore, since the surface of the aluminum foil has irregularities due to rolling, etching pits with excellent uniformity can be obtained by appropriately removing the surface layer portion including the oxide film. At that time, if the removal amount of the surface layer is less than 20 mm, the influence of the unevenness on the surface of the oxide film and the aluminum foil is large, and the uniformity is lowered. On the other hand, when the amount exceeding 200 kg is removed, even the concentrated portion of the reactive substance is removed, so that the reactivity of pit generation is lowered. Therefore, the removal amount of the surface layer portion is more preferably 20 to 200 mm as a thickness in terms of weight , and further preferably a lower limit of 40 mm and an upper limit of 60 mm.

Removal of the surface layer portion on the surface of the aluminum foil can be performed using a general acid solution or alkali solution. However, if a solution with a chlorine ion concentration of 1000 ppm or more is used, or when energization is used together, etching pits are generated sparsely in the removal process, and the surface uniformity is reduced. Therefore, a solution with a chlorine ion concentration of less than 1000 ppm is selected. It is necessary to do.
The removal amount of the surface surface layer part can be calculated by the following numerical formula (1) from the weight loss before and after the reagent immersion.
Single-sided surface layer removal thickness (Å) = ΔW / (S · α) × 10 ⁸ × 1/2 (1)
However, ΔW (weight loss): g / cm ² , S (area): cm ² , α (aluminum oxide density): 2.7 g / cm ³

After the surface surface layer is removed, etching pits can be generated by dipping in an acid solution used for general electrolytic etching. In addition, in order to accelerate the chemical dissolution reaction in the pit generation and the pit diameter expansion described later, there is no problem even if a minute current of 100 mA / cm ² or less is applied.
In addition, as described above, the trace element promotes the generation and growth of etching pits having a depth of, for example, 10 μm or more by causing a local battery reaction with bulk aluminum. However, if the content of the trace elements is less than 20 ppm in total, the generation and growth of etching pits are insufficient and the etching pits are not generated well. On the other hand, if the content of the trace elements exceeds 200 ppm in total, the surface dissolution becomes excessive and the surface dissolution state occurs, and the etching pits are not formed well. For the same reason, it is desirable to set the lower limit to 50 ppm and the upper limit to 150 ppm.

After the etching pit generation process, the foil in which the etching pits are generated is preferably immersed in an acid solution having a chlorine ion concentration of less than 1000 ppm without increasing the number of extra pits as an etching pit hole diameter expansion process. The diameter can be enlarged, and the pit can be grown to a suitable pit diameter. Also in the etching pit hole diameter expanding step, as described above, it is desirable to use a solution having a chlorine ion concentration of less than 1000 ppm. When chlorine ions are contained in an amount of 1000 ppm or more, etching pits are newly generated and pit dispersion becomes non-uniform.
Further, the same solution having a chlorine ion concentration of less than 1000 ppm can be used in the surface layer portion removing step and the etching pit hole diameter expanding step. As a result, the amount of solution used can be reduced, and the labor and space for preparing the solution can be omitted.

As described above, according to the pit generation etching method of the present invention, the total amount of one or more selected from Mn, Zn, Ni, Sn, Ag, Pt, and Au in terms of mass ratio. A surface layer portion on the surface of the aluminum alloy foil containing 20 to 200 ppm, the balance being made of Al and inevitable impurities, without contacting the aluminum alloy foil after the final annealing with a solution having a chlorine ion concentration of less than 1000 ppm. Since the surface layer portion is removed to remove 20 to 200 Å, then the etching pit generation step is performed without applying current or by applying a minute current of 100 mA / cm ² or less , and then the etching pit hole diameter expanding step is performed. Etching pits can be generated uniformly and with high density by electroless, and there is an effect that processing at low cost is possible.

A high-purity aluminum material prepared to be a component of the present invention with a purity of 99.9% or more is prepared. The aluminum material can be obtained by a conventional method, and the production method is not particularly limited in the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used, or a high-purity aluminum material obtained by continuous casting can be used. For example, a sheet material having a thickness of about several mm is formed by the hot rolling or continuous casting rolling. This sheet material is cold-rolled to obtain an aluminum alloy foil of about several tens of μm to 100 μm. In addition, degreasing may be appropriately added during the cold rolling or after the end of the cold rolling, and intermediate annealing may be appropriately added during the cold rolling.
After the final cold rolling, a final annealing heat treatment is usually performed. The heating conditions and the like for the final annealing can be determined by a conventional method. For example, aluminum having an oxide film with an average thickness of 20 to 60 mm by heating in a reducing atmosphere at 500 to 580 ° C. for 3 to 24 hours. Obtain an alloy foil.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching process is performed by a surface layer portion removing process, an etching pit generating process, and an etching pit hole diameter expanding process.
The surface layer portion removing step is performed by dissolving the surface layer portion including the oxide film with a solution having a chlorine ion concentration of less than 1000 ppm. The removal amount at this time is 20 to 200 mm. For removing the surface layer portion, a general acid solution typified by H ₂ SO ₄ , H ₃ PO ₄ , HNO ₃ , and HF, or a mixed solution thereof can be used. The same effect can be obtained even with an alkaline solution.

After the surface layer portion is removed, an etching pit generation step for generating etching pits on the aluminum foil surface is performed.
After the surface surface layer portion is removed, etching pits are generated using an acid solution used for general electrolytic etching. For example, it can carry out by immersing 20 to 120 sec in 60 to 90 degreeC in the solution containing 0.1-3 mol hydrochloric acid and 1-5 mol sulfuric acid with respect to 1 l of solutions. Note that a minute current can be applied if desired.

After the etching pit generation process, an etching pit hole diameter expanding process is performed. In this etching pit hole diameter expanding step, a general acid solution typified by H ₂ SO ₄ , H ₃ PO ₄ , HNO ₃ , or HF, or a mixed solution thereof, or an alkaline solution is used as in the removal of the oxide film. Can be done. Also in the etching pit hole diameter expanding step, it is desirable to use a solution having a chlorine ion concentration of less than 1000 ppm, and the same solution as that used in the surface layer portion removing step can also be used.
As an ideal etching process, after removing the surface oxide film by immersing in 20 to 70 ° C. of 1 to 4 mol / l sulfuric acid for 30 to 500 seconds, 0.1 to 3 mol of hydrochloric acid and 1 sulfuric acid are added to 1 l of the solution. This is a method of increasing the pit diameter by immersing in a solution containing ˜5 mol for 60 to 90 ° C. for 20 to 120 seconds to generate etching pits and further immersing in 1 to 4 mol / l sulfuric acid 60 to 90 ° C. for 400 to 1000 seconds.

  In the etching process, pits are formed at a high density on the foil by setting the components and the use solution, and a high roughening rate is obtained. This foil is subjected to a chemical conversion treatment to obtain a necessary withstand voltage, and then a capacitor having a high capacitance is obtained by incorporating it as an electrode in an electrolytic capacitor by a conventional method.

  The present invention is preferably used as an anode of a medium-high voltage electrolytic capacitor. However, the present invention is not limited to this, and can be used for a capacitor having a lower formation voltage. It can also be used as a cathode material.

  Aluminum slab having an Al purity of 99.9% or more and containing 20 to 200 ppm of one or more elements selected from Mn, Zn, Ni, Sn, Ag, Pt, and Au as shown in Table 1, and other inevitable impurities In accordance with an ordinary method, homogenization treatment and soaking treatment were performed, and hot rolling and cold rolling were performed to obtain a 110 μm aluminum foil. This foil was heat-treated at 520 ° C. for 6 hours in an argon atmosphere to produce a soft foil having a self-reactivity of 110 μm with a cubic rate of 95% or more. An oxide film having an average thickness of 45 mm was formed on the surface of the soft foil.

This aluminum foil was immersed in a 3 mol / l sulfuric acid solution (chlorine ion concentration 20 ppm) at 40 ° C. to remove the surface layer portion including the oxide film. When removing the surface layer portion, the immersion time was changed, and as shown in Table 1, the removal amount of the surface layer portion was changed. In addition, the removal amount (thickness) of the surface layer portion was calculated using the above formula (1) using sulfuric acid as a reagent. After removing the surface layer portion, it was washed with water and immersed in a solution containing 1 mol of hydrochloric acid and 3 mol of sulfuric acid at 70 ° C. and 1 l of solution to generate etching pits. At that time, a direct current having a current density of 10 to 200 mA / cm ² (per one side) was applied to some aluminum foils for 60 seconds. After the pit was generated, it was washed with water and immersed in a 3 mol / l sulfuric acid solution (chlorine ion concentration 20 ppm) at 75 ° C. for 600 sec to enlarge the pit diameter. After expanding the pit diameter, it was washed with ion-exchanged water and dried.

The obtained etching foil was formed at 300 V with a 10 wt% boric acid solution, and the capacitance was evaluated.
As shown in Table 1, when the trace element defined in the present invention is added, an appropriate capacity is obtained even by electroless melting without flowing current in the pit generation process, and it can be seen that the etching pits grow normally. . It can also be seen that a high capacitance can be obtained when the removal amount of the surface layer containing the oxide film is 20 to 200 mm. Furthermore, it can be seen that such a foil has no characteristic difference even when electrolytic etching is performed, and the influence of the surface oxide film is large.
Moreover, even if the trace element of the present invention is added as in the comparative example, when the surface layer removal amount is small or excessive, a decrease in capacitance is observed. Furthermore, even when the trace element content was not appropriate, a high capacitance was not obtained.

For comparison, the aluminum foil with 130 ppm Ni obtained in Example 1 was used and immersed in a solution containing 3 mol sulfuric acid and 1 mol hydrochloric acid per liter of the solution at 40 ° C., 3 mol sulfuric acid solution (chlorine ion concentration 10 ppm) or 40 ° C. Then, the surface layer portion of 40 mm including the oxide film was removed in terms of mass. After removing the surface layer portion, it was washed with water and immersed in a solution containing 1 mol of hydrochloric acid and 3 mol of sulfuric acid per liter of solution at 70 ° C. to generate etching pits. After the pit is generated, it is washed with water and immersed in a solution containing 3 mol / l sulfuric acid and 1 mol hydrochloric acid at 85 ° C., 3 mol / l sulfuric acid solution (chlorine ion concentration 10 ppm) or 1 liter of solution at 85 ° C. for 600 sec. Enlarged. After expanding the pit diameter, it was washed with ion-exchanged water and dried. In the comparative example, a solution containing hydrochloric acid was used in at least one treatment of the surface layer removal and pit hole diameter expansion.
The obtained etching foil was formed at 300 V with a 10 wt% boric acid solution, and the capacitance was evaluated. In addition, the bending strength of each test material was measured, and relative evaluation was performed based on the test material of Example 1. The results are shown in Table 2. The measurement test was carried out in accordance with JIS P 8115: 2001 paper and paperboard − folding strength test method − MIT testing machine method, conditions of φ1.0 mm, 250 g load, and bending angle 90 degrees. Below, one round trip was evaluated at a time.

  When surface layer removal is performed with a solution containing hydrochloric acid (chlorine ion concentration of 1000 ppm or more) compared to when removing the surface layer portion and increasing the pore size with a solution containing no hydrochloric acid (chlorine ion concentration less than 1000 ppm) Shows a decrease in capacitance and bending strength. Furthermore, when the pore size is expanded with a solution containing hydrochloric acid (chlorine ion concentration of 1000 ppm or more), the bending strength is significantly reduced. This is because the generation of pits is promoted by the entry of hydrochloric acid, and as a result, pits are generated at the surface layer removal stage and pits grow when the hole diameter is expanded. As described above, when etching a foil in which pits grow electrolessly, a high-capacity foil can be obtained by selecting a solution having a chlorine ion concentration of less than 1000 ppm in removing the surface layer. In addition, a high-strength foil can be obtained by selecting a solution having a chlorine ion concentration of less than 1000 ppm even when the pore size is enlarged.

Claims (4)

After final annealing, containing one or more selected from Mn, Zn, Ni, Sn, Ag, Pt, Au in a mass ratio of 20 to 200 ppm in total, with the balance consisting of Al and inevitable impurities The surface layer part removal which removes the surface layer part including the oxide film on the surface of the aluminum alloy foil with a removal thickness of 20 to 200 mm without contacting the aluminum alloy foil with a solution having a chlorine ion concentration of less than 1000 ppm. And then performing an etching pit generating step by applying a small current of 100 mA / cm ² or less without energization , and then performing an etching pit hole diameter expanding step. The pit diameter enlarging step, the pit generation etching method according to claim 1, wherein the chloride ion concentration is performed by contacting a solution of less than 1000ppm in the aluminum alloy foil. 3. The pit generation etching method according to claim 2, wherein the surface layer portion removal and the etching pit hole diameter expanding step are performed using the same solution having a chlorine ion concentration of less than 1000 ppm. The pit generation etching method according to any one of claims 1 to 3 , wherein the etching pit generation step is performed by bringing a solution containing hydrochloric acid of 0.1 mol / l or more into contact with the aluminum alloy foil.