JPS6337490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an aluminum anode foil for an electrolytic capacitor. For details, 0.007-0.2%
Contains iron (all weight percentages are expressed below unless otherwise specified), 0.009 to 0.2% silicon, titanium content of 3 ppm or less, and magnesium, manganese, copper, zinc, and nickel content, respectively.
30ppm or less and purity 99.6-99.98%
The present invention relates to a method for manufacturing an aluminum anode foil for electrolytic capacitors, which is made of aluminum and has electrolytic foil properties equivalent to anode foils made of aluminum with a purity of 99.99% or more. Aluminum foil for electrolytic capacitor anodes has traditionally been manufactured by surface-treating aluminum foil made from high-purity secondary electrolytic aluminum (purified aluminum manufactured using a three-layer electrolytic method, purity 99.99% or higher). According to the typical method, a slab of secondary electrolytic aluminum is hot-rolled to a thickness of about 5 mm, then cold-rolled to form a foil sheet of about 0.5 mm, and then cold-rolled to form a foil material of about 0.5 mm. The thickness of the foil shall be .
The thickness of the foil varies depending on the application, but it is usually around 60-90μ for low-voltage capacitors of 100V or less, and around 100μ for high-voltage capacitors of 150V or more. The foil is then etched to provide irregularities on the surface and increase the substantial surface area, and then anodized to form a dielectric film on the surface, thereby producing an anode aluminum foil. Surface treatment conditions also vary depending on the use of the foil, but etching is usually carried out by electrolytic etching using alternating current or direct current in an aqueous chloride solution or an aqueous chloride solution containing additives such as sulfuric acid, nitric acid, or phosphoric acid. Further, anodization is performed in an aqueous solution of boric acid or phosphoric acid containing ammonium. The production of anode aluminum foil using this conventional method requires secondary electrolytic aluminum as a material, but secondary electrolytic aluminum is significantly more expensive than primary electrolytic aluminum (aluminum produced by electrolyzing alumina). Therefore, the aluminum foil manufactured from now on will inevitably be expensive. The reason why primary electrolytic aluminum cannot be used in the production of aluminum foil for anodes is that while secondary electrolytic aluminum has a purity of 99.99% or higher,
This is because electrolytic aluminum has a maximum purity of 99.9%. In other words, primary electrolytic aluminum usually contains 0.1% of unavoidable impurities such as iron, silicon, copper, and titanium.
This is because these elements not only reduce the capacitance of the aluminum anode foil but also increase leakage current. However, it is generally recommended that the content of iron and titanium in aluminum anode foil be 0.001% or less, and that the content of silicon and copper be 0.005% or less each. Currently, secondary electrolytic aluminum, which is expensive but has extremely low impurity content, must be used as a material. In order to obtain an aluminum anode foil using primary electrolytic aluminum as a material and having electrolytic foil characteristics equivalent to high-purity aluminum anode foil manufactured using secondary electrolytic aluminum, the present inventors have determined the amount of impurity elements in the electrolytic foil. As a result of intensive research into the relationship between capacitance and other electrolytic foil properties, we found that if the titanium content in aluminum anode foil is extremely small, iron, silicon, and A new finding was obtained that the electrolytic foil properties do not deteriorate even if a small amount of impurity elements such as copper are present in the foil. Therefore, we actually manufactured anode foils using aluminum from which titanium had been separated and removed from primary electrolytic aluminum base metals of various purity, and measured the electrolytic foil characteristics of this anode foil. It was discovered that the electrolytic foil has properties equivalent to anode foils manufactured from aluminum base metal, and the present invention was achieved. In addition, in order to separate and remove titanium from the primary electrolytic aluminum ingot to produce aluminum for anode foil material, it is sufficient to add boron to the molten aluminum and separate and remove the titanium in the molten metal as a titanium-boron compound. I also found That is, an object of the present invention is to provide an aluminum anode foil for electrolytic capacitors which has electrolytic foil properties equivalent to anode foils manufactured from secondary electrolytic aluminum even though the aluminum purity is almost the same as that of primary electrolytic aluminum. However, this purpose is
A method for producing aluminum anode foil for electrolytic capacitors, in which aluminum foil is produced by casting and rolling from molten aluminum, and a dielectric film is formed on the surface of the foil, including 0.007 to 0.2% iron, 0.009 to 0.2% iron;
% silicon, titanium exceeding 5 ppm, magnesium, manganese, copper, zinc, and nickel content of 30 ppm or less, and purity of 99.6~
Boron is added to 99.98% molten aluminum to generate a titanium-boron compound, and the titanium-boron compound is separated and removed from the molten metal to produce aluminum foil from the molten aluminum with a titanium content of 3 ppm or less. Contains 0.007~0.2% iron, 0.009~0.2% silicon,
Titanium content is less than 3ppm, magnesium,
The content of manganese, copper, zinc and nickel is 30ppm or less each, and the purity is 99.6~
This is achieved by a method for manufacturing aluminum anode foil for electrolytic capacitors consisting of 99.98% aluminum. Next, the present invention will be explained in detail. In the method for producing an aluminum anode foil of the present invention, the titanium content in the foil is 3 ppm or less.
The higher the titanium content, the lower the capacitance of the anode foil, but especially when the amount exceeds 5 ppm, titanium, along with iron and silicon, will affect the leakage current characteristics, the voltage resistance of the foil,
Adversely affects electrolytic foil properties such as heat resistance. In the present invention, as long as the titanium content in the foil is 3 ppm or less, even if iron and silicon are contained in the foil to the same extent as in a normal primary electrolytic aluminum ingot, the characteristics of the electrolytic foil will be affected. There are no particular negative effects. However, if the content of iron or silicon in the foil exceeds 0.2%, sufficient capacitance cannot be obtained.
0.007 to 0.2%, preferably 0.03 to 0.2%, more preferably 0.03 to 0.1%, and the silicon content is 0.009 to 0.2%.
The content is 0.2%, preferably 0.01-0.2%, more preferably 0.01-0.1%. Other impurities contained in the primary electrolytic aluminum ingot include magnesium, manganese,
There are copper, zinc, nickel, chromium, and vanadium, and there is no problem if these elements are contained in the amount contained in the primary electrolytic aluminum ingot with a purity of 99.6% or more, but if the content is large, Reduces the capacitance of the foil. Therefore, the content of magnesium, manganese, copper, zinc, and nickel in the foil of the present invention is each 30 ppm or less. Further, it is preferable that chromium and vanadium are each 20 ppm or less, particularly 10 ppm or less. Although boron is not an inevitable impurity in aluminum, in the method of the present invention, boron is added to the molten aluminum when removing titanium from the molten aluminum, resulting in a small amount of boron being contained in the anode foil. It turns out. Since boron does not have a positive effect on the properties of the electrolytic foil, it is desirable that its content is usually 30 ppm or less, particularly 20 ppm or less. The anode foil of the present invention is mainly manufactured using a primary electrolytic aluminum base metal as a material. Primary electrolytic aluminum usually contains 0.02-0.2% iron, 0.02-0.2% silicon, and
0.001-0.004% (10-40ppm) titanium, 0.0005
Contains ~0.003% (5ppm~30ppm) of chromium, vanadium, and less than 0.003% (30ppm) of copper. As mentioned above, if the content of these impurity elements is too large, it will adversely affect the characteristics of the anode foil, so it is desirable to use primary electrolytic aluminum base metal with the highest possible purity as the material.
It is also difficult to obtain primary electrolytic aluminum ingots with very high purity. Therefore, in the present invention, 99.6 to 99.98% (iron content 0.007 to 0.2%, silicon content 0.009 to 0.2%), preferably 99.6 to 99.95%
(Iron content 0.03-0.2%, silicon content 0.01-0.2%),
More preferably 99.8-99.95% (iron content 0.03-99.95%)
An aluminum base metal with a purity of 0.1% and silicon content of 0.01 to 0.1% is used as the material. In this case, if the purity of the primary electrolytic aluminum used as the raw material is low, a small amount of secondary electrolytic aluminum may be added to it to increase its purity. To manufacture the anode foil of the present invention, first, titanium is decomposed and removed from aluminum of the above purity to reduce the titanium content to 3 ppm or less. To remove titanium, boron is added to molten aluminum at 750 to 800°C to form a compound of titanium and boron in aluminum, and then the titanium-boron compound is removed by leaving the molten metal for 2 to 24 hours. All you have to do is let it settle to the bottom of the molten metal and collect the supernatant part of the molten metal. In this case, instead of letting the molten metal stand still,
Sedimentation of the titanium-boron compound in the molten metal may be accelerated by a centrifuge. As the boron added to the molten metal, it is preferable to use an aluminum-boron mother alloy or potassium borofluoride. In addition, as a method for removing titanium from molten aluminum, boron is added to the electrolytic bath in the alumina electrolytic reduction tank, and a titanium-boron compound is formed in the aluminum metal layer formed at the bottom of the reduction tank. It is also possible to adopt a method of separating titanium from. As the boron added to the electrolytic bath, boron trioxide is preferable. When boron is added to molten aluminum, impurity elements such as vanadium and chromium contained in the molten metal will also form compounds with boron, so these impurity elements can be removed by settling them at the bottom of the molten metal in the same way as with titanium. It can be removed from the molten metal. The amount of boron added to the molten aluminum is usually 0.4 to 1.0 times the total weight of titanium, vanadium, and chromium contained in the molten aluminum. After separating and removing titanium from the molten aluminum, a slab is cast using a vertical or horizontal semi-continuous casting method, and then a foil with a thickness of 60 to 120μ is produced from this slab by hot rolling, cold rolling, and then foil rolling. Manufacture. In the present invention, when producing foil from molten metal, molten aluminum is passed between the driving molds through a nozzle placed between the driving molds, such as two rotating casting rolls or a pair of running casting belts. The foil manufacturing method to be introduced is the so-called direct continuous casting and rolling method, in which plates with a thickness of 3 to 25 mm are directly cast from the molten metal, and then cold rolled and foil rolled to a thickness of 60 to 25 mm.
Foils with a thickness of 120μ can be produced. The direct continuous casting and rolling method itself uses these two rotating rolls or a pair of running belts as the casting mold.
It is known as the 3C method, Hunter method or Hazeley method (for example, Patent Nos. 243465 and 247991).
If a foil is produced from a plate cast by this direct continuous casting and rolling method, it can be rolled into a foil by only cold rolling without hot rolling. This method has the advantage that the amount of crystallized substances due to impurity elements in the foil is small and the size thereof is also small, so that the electrolytic foil properties of the foil, particularly the leakage current properties, are improved. In this case, the casting speed is 0.8~1.4m/min, and the molten metal temperature is 680~
710℃ is suitable. The aluminum foil produced in this way is softened by annealing, then etched to enlarge the actual surface of the foil, and then anodized to form a dielectric film on the surface. , aluminum anode foil. As explained in detail above, according to the present invention, even if an aluminum base metal with a purity of 99.6 to 99.98% is used as a material, the aluminum has electrolytic foil properties equivalent to anode foils with an aluminum purity of 99.99% or more. It is possible to provide an anode foil. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Examples 1 to 7, Reference Example 1 and Comparative Examples 1 to 5 500 kg of aluminum ingots of various purity numbered 1 to 8 shown in Table 1 were melted in a gas furnace, and a mixed gas of chlorine and nitrogen was thoroughly dried. It was blown into molten metal at 750°C for 3 minutes to perform degassing treatment. Next, aluminum-boron mother alloy (boron content 3%) was added as boron to the molten metals numbered 1 to 7.
After adding 400 g or 250 g of potassium boron fluoride and thoroughly stirring the molten metal, the boron-titanium compound was allowed to settle at the bottom of the molten metal by allowing it to stand for 2 hours or more. After this, the upper molten metal of the gas furnaces numbered 1 to 6 was taken and directly cast to a radius of 30cm according to the continuous casting and rolling method.
is introduced between two rotating rolls, and the casting speed is increased.
A 6 mm thick plate was cast at 1 m/min. On the other hand, for the gas furnace No. 7, the upper molten metal was taken in the same way, and it was cast using a vertical semi-continuous casting method with a cross section of 32 cm
A 70 cm slab was cast and hot rolled at 450 to 500°C to form a 6 mm thick plate. After degassing the molten metal No. 8, a plate with a thickness of 6 mm was similarly cast by direct continuous casting and rolling, omitting the boron addition treatment. These plates were then cold rolled and foil rolled to final form a 65μ foil. The composition and component amount (ppm) of the aluminum foil thus produced are also shown in Table 1. Then, these aluminum foils are placed in a vacuum.
The foil was annealed at 350°C for 2 hours and etched under the following conditions. Etching processing conditions Etching solution: mixed aqueous solution consisting of 6% hydrochloric acid, 0.3% nitric acid, 0.1% phosphoric acid and 0.01% sulfuric acid Etching temperature: 52 ± 1°C Current density (AC): 75 A/dm ² Etching time: 2 minutes Etching processing After that, these foils were washed, and then cut into two foils A and B, each measuring 100 m x 150 mm. Foils A and B were subjected to chemical conversion treatment under the following conditions, and a dielectric of aluminum oxide was applied to the foil surface. A film was formed. Chemical treatment conditions Chemical solution: 100g of boron + 3.5ml of 28% ammonia water
+ Pure water 1 Forming temperature: 70°C Forming time: 20 minutes Forming voltage: 15 V After this, the two foils A and B on which the dielectric film was formed were transferred to a 5% ammomonium borate aqueous solution at 20°C, and heated with alternating current. Capacitance was measured using a bridge. In Experimental Example Nos. 4, 6, and 7, the leakage current value for one sheet of foil A was also measured. These results are shown in Table 1 as Examples 1 to 7 and Reference Example 1. For comparison, anode foils were manufactured in exactly the same manner as in the above example, except that the separation and removal of titanium by boron addition from molten aluminum of various purity was omitted, and the capacitance thereof was measured. (The leakage current value was also measured for Example No. 13.) The results are shown in Table 1 as Comparative Examples 1 to 5. In addition, in Experimental Example Nos. 1, 2, 8, and 9, a mixture of primary electrolytic aluminum ingot and secondary electrolytic aluminum ingot was used as the material, in Comparative Example 5, secondary electrolytic aluminum ingot was used, and in the other cases, All 1
An electrolytic aluminum base metal was used. As is clear from Table 1, even if the anode foil obtained according to the method of the present invention is made of primary electrolytic aluminum, if the titanium content is 3 ppm or less,
Shows the same capacitance as anode foil made from electrolytic aluminum base metal. In addition, if the foil is manufactured using a thin plate manufactured by the direct casting and rolling method as a base material and the amount of boron in the foil is reduced, the leakage current characteristics of the anode foil of the present invention are improved, and the secondary electrolytic aluminum base material is It has the same performance as anode foil made from. 【table】

Claims (1)

[Claims] 1. A method for producing an aluminum anode foil for an electrolytic capacitor, in which aluminum foil is produced from molten aluminum by casting and rolling, and a dielectric film is formed on the surface of the foil, including 0.007 to 0.2% iron, 0.009 to 0.
Contains 0.2% silicon, more than 5ppm titanium, contains less than 30ppm each of magnesium, manganese, copper, zinc and nickel, and has purity.
Boron is added to 99.6 to 99.98% molten aluminum to generate a titanium-boron compound, and the titanium-boron compound is separated and removed from the molten metal to produce aluminum foil from the molten aluminum with a titanium content of 3 ppm or less. Contains 0.007~0.2% iron, 0.009~0.2% silicon, titanium content is 3ppm or less, magnesium, manganese, copper, zinc and nickel content is 30ppm or less each. , and purity
A method for producing aluminum anode foil for electrolytic capacitors consisting of 99.6-99.98% aluminum. 2. In the method according to claim 1, the molten aluminum to which boron is added has a concentration of 0.03 to
Contains 0.2% iron, 0.01~0.2% silicon, more than 5ppm titanium, contains less than 30ppm each of magnesium manganese, copper, zinc and nickel, and is 99.6~99.95% pure aluminum molten metal. A method for producing aluminum anode foil for electrolytic capacitors. 3 In the method according to claim 2, the molten aluminum to which boron is added has a concentration of 0.03 to
It is molten aluminum containing 0.1% iron, 0.01~0.1% silicon, 10~40ppm titanium, and the content of magnesium, manganese, copper, zinc, and nickel is less than 30ppm each, and has a purity of 99.8~99.95%. A method for producing aluminum anode foil for electrolytic capacitors, characterized by the following. 4. An electrolytic capacitor according to the method according to any one of claims 1 to 3, characterized in that the boron added to the molten aluminum is an aluminum-boron mother alloy and/or potassium boron fluoride. Method for manufacturing aluminum anode foil. 5. In the method according to any one of claims 1 to 4, the amount of boron added is
Based on the total weight of titanium, chromium and vanadium contained in molten aluminum, as boron
A method for producing aluminum anode foil for electrolytic capacitors, characterized in that the amount is 0.4 to 1.0 times. 6. In the method according to any one of claims 1 to 5, the casting and rolling method continuously casts molten aluminum into a strip-shaped cast plate using a driven mold, and then cools it. 1. A method for producing aluminum anode foil for electrolytic capacitors, characterized in that the method involves rolling.