JPH0330283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aluminum anode foil for electrolytic capacitors. In detail, 0.007 to 0.2% (hereinafter, all weight percentages are expressed unless otherwise specified) of iron,
Contains 0.009-0.2% silicon and titanium content
5ppm or less, magnesium, manganese, copper,
Aluminum for electrolytic capacitors, which is made of aluminum with a zinc and nickel content of 30 ppm or less and a purity of 99.6 to 99.98%, and has electrolytic foil properties equivalent to anode foils made of aluminum with a purity of 99.99% or more. Regarding anode foil. 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 more,
This is because electrolytic aluminum has a maximum purity of 99.9%. In other words, primary electrolytic aluminum contains iron,
Unavoidable impurities such as silicon, copper, and titanium are usually
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 an extremely low amount of impurities, has no choice but to 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 electrolytic foil properties such as electrostatic capacitance, 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 produced 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 properties of these anode foils. 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
Contains 0.007-0.2% iron, 0.009-0.2% silicon,
Titanium content is less than 5ppm, magnesium,
The content of manganese, copper, zinc and nickel is 30ppm or less each, and the purity is 99.6~
This is achieved by an aluminum anode foil for electrolytic capacitors consisting of 99.98% aluminum. Next, the present invention will be explained in detail. In the aluminum anode foil of the present invention, the titanium content must be 5 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, has a negative effect on electrolytic foil properties such as leakage current characteristics, pressure resistance, and heat resistance of the foil. give. Therefore, the titanium content should be 5 ppm or less, preferably
Should be 3ppm or less. In the present invention, as long as the titanium content in the foil is 5 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.
0.007-0.2%, preferably 0.03-0.2%, more preferably 0.03-0.1%, and the silicon content is 0.009
~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, boron is added to the molten aluminum when removing titanium from the molten aluminum.
A small amount of boron will be contained in the anode foil. 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 and 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
An aluminum base metal with a purity of 0.03 to 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. In order to produce the anode foil of the present invention, first, titanium is separated and removed from aluminum of the above purity to reduce the titanium content to 5 ppm or less, preferably 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 allowing the molten metal to stand 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. A method of separating titanium can also be adopted. 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 melting 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 a 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. According to this method, 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, which is an advantage. In this case, the casting speed is 0.8 to 1.4 m/min, and the molten metal temperature is 680 m/min.
~710°C is suitable. The aluminum foil produced in this way is softened by annealing, then etched to expand the effective surface area 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 characteristics equivalent to an anode foil 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 the gist thereof is exceeded. Examples 1 to 8 and Comparative Examples 1 to 5 500 kg of aluminum ingots of various purity numbers 1 to 8 shown in Table 1 were melted in a gas furnace, and a well-dried mixed gas of chlorine and nitrogen was added to the molten metal at 750°C. It was blown into the tank 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.
was introduced between two rotating rolls, and the casting speed was 1.
A plate with a thickness of 6 mm was cast at m/min. On the other hand, number 7
For the gas furnace, the upper molten metal was taken in the same way, and it was cast into a 32 cm cross section by vertical semi-continuous casting method.
A 70 cm slab was cast and hot rolled at 450 to 500°C to form a 6 mm thick plate. Regarding the molten metal No. 8, after degassing treatment, a plate with a thickness of 6 mm was similarly cast according to the direct continuous casting and rolling method, omitting the boron addition treatment. These plates were then cold rolled and foil rolled into a final 65μ foil. The composition and component amount (ppm) of the aluminum foil thus produced are also shown in Table 1. These aluminum foils were then heated in vacuum at 350°C.
The foil was annealed at ℃ for 2 hours, and etching treatment was performed on the annealed foil 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 mm x 150 mm. Foils A and B were subjected to a chemical conversion treatment under the following conditions, and the foil surface was coated with an aluminum oxide dielectric. A film was formed. Chemical treatment conditions Chemical liquid: 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% boron ammonium aqueous solution at 20°C, and heated using an AC bridge. Capacitance was measured. 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 8. For comparison, anode foils were manufactured in exactly the same manner as in the above example, except that the separation and removal of boron-added titanium from molten aluminum of various purity was omitted, and the capacitance thereof was measured. (The leakage current value was also measured for Experimental 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, the anode foil of the present invention has 1
Even if secondary electrolytic aluminum is used as a material, if the titanium content is 5 ppm or less, it exhibits the same capacitance as an anode foil made of secondary 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. Contains 0.007 to 0.2% iron, 0.009 to 0.2% silicon, titanium content is 5 ppm or less, and magnesium, manganese, copper, zinc, and nickel content is each 30 ppm or less. , and the purity is
Aluminum anode foil for electrolytic capacitors consisting of 99.6~99.98% aluminum. 2. In the aluminum anode foil according to claim 1, the iron content in the aluminum is
Aluminum anode foil for electrolytic capacitors with silicon content of 0.03-0.2% and 0.01-0.2%. 3 In the aluminum anode foil according to claim 2, the iron content in the aluminum is
Aluminum anode foil for electrolytic capacitors with silicon content of 0.03-0.1% and 0.01-0.1%. 4. The aluminum anode foil for an electrolytic capacitor according to any one of claims 1 to 3, wherein the titanium content in the aluminum is 3 ppm or less, and the chromium and vanadium contents are each 20 ppm or less. . 5. The aluminum anode foil for an electrolytic capacitor according to claim 4, wherein the chromium and vanadium contents in the aluminum are each 10 ppm or less.