JPH0727845B2 - Solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor.

2. Description of the Related Art A solid electrolytic capacitor is formed by forming an oxide layer, which is a dielectric, on the surface of a valve metal substrate that constitutes an anode, and sequentially stacking a semiconductor layer and a conductor layer on the oxide layer.

As a valve metal forming the anode, a metal having a valve action such as aluminum, tantalum, niobium, and titanium is used, and among these, aluminum and tantalum are often used. The shape of the anode valve metal substrate is a porous sintered body, a plate (foil), a linear shape, or the like, and a capacitor of the type in which the plate (foil) is spirally wound can be a small-sized and large-capacity capacitor.

However, even with this spirally wound type capacitor,
An electrolytic capacitor using a conventional electrolytic solution and JP-A-58-17609
A capacitor of a type in which two electrode foils are sandwiched between separator sheets and wound, like the capacitor using TCNQ salt described in Japanese Patent Publication, has a limit in reducing the volume because of its structure.

In addition, when an electrolyte or TCNQ salt is used, the electric conductivity is 10 ^-1 S
・ Small as cm ^-1 or less, loss factor of capacitor (tanδ)
It did not affect the performance such as impedance characteristics.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to solve the problems of the prior art and to provide a solid electrolytic capacitor which is smaller in size and volume than conventional products and has good capacitor performance.

Means for Solving the Problems The present invention provides a solid electrolytic capacitor that can achieve the above object.

That is, the present invention has a semiconductor layer containing lead dioxide and lead sulfate as main components and a conductor layer sequentially on the oxide layer of the anode valve metal base which is spirally wound with an oxide layer on the surface. The present invention relates to a solid electrolytic capacitor that is formed.

The solid electrolytic capacitor of the present invention will be described below.

As the valve metal substrate used as the anode, any of metals having valve action such as aluminum, tantalum, niobium, titanium, and alloys having these as substrates may be used. Of these, it is advantageous to use aluminum. The shape of the anode substrate before being formed into a spiral shape is usually a plate shape (including foil, ribbon, etc.).

The oxide layer on the surface of the anode substrate may be the oxide layer of the anode substrate itself provided on the surface layer portion of the anode substrate, or may be another dielectric oxide layer provided on the surface of the anode substrate. May be. Of these, a layer made of an oxide of the anode valve metal itself is desirable. In either case, a conventionally known method can be used as a method for providing the oxide layer.

For example, when using an aluminum foil as the anode substrate,
When the surface of the aluminum foil is electrochemically etched and further electrochemically treated in an aqueous solution of boric acid and ammonium borate, an oxide layer made of an alumina dielectric is formed on the aluminum foil as the anode substrate. . The anode lead wire is connected to the anode valve metal substrate before and after the oxide layer is provided by caulking, high-frequency bonding, or the like.

In order to form the anode valve metal substrate in a spiral shape, in the method of producing a wound element composed of the positive and negative bipolar foil used in an electrolytic capacitor using a conventional electrolytic solution, a method of winding only the anode is used. And has a spiral shape as shown in FIG. 1, for example. The number of windings, the winding diameter, the winding pitch, etc. can be determined as desired and are not particularly limited. Among these, it is preferable to wind the anode valve metal substrate in consideration of the pre-arrangement so that the semiconductor layer and the conductor layer can be successfully formed on the oxide layer.

It should be noted that reforming can be performed when a crack is generated in an oxide layer provided in advance during molding. The re-formation method may be any conventionally known method. For example, the above-described electrochemical treatment of aluminum foil in an aqueous solution of boric acid and ammonium borate is applied.

The semiconductor layer used in the present invention is composed of a layer containing lead dioxide and lead sulfate as main components.

When the semiconductor layer is composed of a layer containing lead dioxide, which originally serves as a semiconductor, and lead sulfate, which is an insulating material, as a main component, the leakage current value of the capacitor can be reduced by mixing lead sulfate. On the other hand, since the electrical conductivity of the semiconductor layer becomes low due to the incorporation of lead sulfate, the loss factor (tan
It has been found by the present invention that δ) becomes large, but a high level of performance is maintained and exhibited even when compared with the conventional solid electrolytic capacitor. Therefore, when the semiconductor layer is composed of a mixture of lead dioxide and lead sulfate, the content of lead dioxide in the semiconductor layer is in the range of 10 wt% or more and less than 100 wt%, preferably 10 to 95 wt% lead dioxide. On the other hand, a wide range of composition of 90 to 5% by weight of lead sulfate can maintain and develop good capacitor performance, but especially 20 to 50% by weight of lead dioxide.
On the other hand, in the range of 80 to 50% by weight of lead sulfate, and in the range of 75 to 65% by weight of lead sulfate to 25 to 35% by weight of lead dioxide, the balance between the leakage current value and the loss coefficient is particularly good. Lead dioxide
If it is less than 10% by weight, the electroconductivity deteriorates and the loss factor increases, and the capacity is not sufficiently expressed. If the lead dioxide content is 100% by weight, the leakage current value becomes large, and a lot of time is required for post-chemical formation or aging after the capacitor is manufactured, which is disadvantageous in terms of cost.

The semiconductor layer containing lead dioxide and lead sulfate as main components can be formed by chemical deposition using, for example, an aqueous solution containing lead ions and persulfate ions as a reaction mother liquor.

The concentration of lead ions in the reaction mother liquor is within a range from 0.1 mol / l to a concentration giving a saturated solubility, preferably from 0.5 mol / l to a concentration giving a saturated solubility. When the concentration of lead ions is higher than the concentration that gives the saturated solubility, the merit of increasing the amount is not recognized.

If the concentration of lead ions is lower than 0.1 mol / l,
Since the lead ion concentration in the reaction mother liquor is too low, there is a problem that the number of times of coating must be increased. On the other hand, the concentration of persulfate ion in the reaction mother liquor is molar ratio to lead ion.
It is within the range of 0.05 to 5. If the concentration of persulfate ion is more than 5 with respect to the lead ion, unreacted persulfate ion remains, resulting in higher cost, and the concentration of persulfate ion is less than 0.05 with respect to the lead ion. If so, unreacted lead ions remain and the electrical conductivity deteriorates, which is not preferable.

In the present invention, another oxidizing agent containing no persulfate ion may be added to the reaction mother liquor. The blending amount of the oxidizer is determined by preliminary experiments in order to keep the leakage current value and the loss coefficient value of the manufactured capacitor in a well-balanced manner.

Typical examples of compounds that give lead ion species include lead citrate, lead perchlorate, lead nitrate, lead acetate, basic lead acetate, lead chlorate, lead sulfamate, lead hexafluorofluoride, lead bromate, Examples include lead chloride and lead bromide. Two or more kinds of compounds that give these lead ion species may be mixed and used. On the other hand, potassium persulfate, sodium persulfate, ammonium persulfate and the like are typical examples of the compound that gives a persulfate ion species. Two or more kinds of these compounds giving the persulfate ion species may be mixed and used.

Examples of the oxidizing agent include hydrogen peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate, calcium perchlorate and the like.

The conductor layer provided on the semiconductor layer can be provided by, for example, solidifying a conductive paste, plating, metal deposition, formation of a heat-resistant conductive resin film, or the like. As the conductive paste, silver paste, copper paste, aluminum paste,
Carbon paste, nickel paste, etc. are preferred,
These may be used alone or in combination of two or more. When two or more kinds are used, they may be mixed to form a layer, or may be stacked as another layer. After applying the conductive paste, leave it in the air or heat it to solidify.

Examples of the plating include nickel plating and copper plating. Aluminum, copper and the like can be used as the vapor deposition metal.

The cathode terminal can be mounted on the conductor layer using, for example, a conductive paste, or can be soldered on the conductive paste after it solidifies.

The solid electrolytic capacitor of the present invention configured as described above can be made into a general-purpose capacitor product for various applications by, for example, a resin mold, a resin case, a metal outer case, a resin dipping, an outer case such as a laminated file. it can.

EFFECTS OF THE INVENTION The solid electrolytic capacitor of the present invention can be further reduced in size and volume as compared with the conventional electrolytic capacitor, and has good capacitor performance.

EXAMPLES Hereinafter, the present invention will be described in more detail by showing examples. The characteristic values of the solid electrolytic capacitors of each example are shown in Table 1.

Example 1 An aluminum foil having a length of 10 cm and a width of 0.5 cm was used as an anode, and the surface of the foil was electrochemically etched by an alternating current. Then, crimp the anode terminal to the etched aluminum foil,
The anode lead wire was connected. Subsequently, it is electrochemically treated in an aqueous solution of boric acid and ammonium borate to form an oxide layer of alumina.
1.0 μF / cm ² ) was obtained. Next, after winding this chemical conversion foil, re-chemical conversion was performed in the above-mentioned aqueous solution of boric acid and ammonium borate.

Reaction by mixing lead acetate trihydrate aqueous solution with a lead acetate trihydrate concentration of 3.8 mol / l and ammonium persulfate aqueous solution with a molar ratio of 1: 1 (volume ratio) of ammonium persulfate concentration of 4.0 mol / l Mother liquor was obtained. The above wound foil was immersed in this reaction mother liquor and left at 80 ° C. for 20 minutes. The semiconductor layer deposited on the winding foil was thoroughly washed with water to remove unreacted materials, and then dried under reduced pressure at 100 ° C. for 1 hour. The produced semiconductor layer was composed of lead dioxide and lead sulfate, and it was confirmed by mass spectrometry, X-ray analysis and infrared spectroscopy that lead dioxide was contained in an amount of about 25% by weight.

Next, the wound foil having a semiconductor layer made of lead dioxide and lead sulfate was immersed in a silver paste bath, pulled up, and then air dried. The solidified silver paste layer was formed on the semiconductor layer of the rolled foil. A copper wire was used as a cathode lead, which was connected to a winding foil with a silver paste and then sealed with a resin to produce a solid electrolytic capacitor.

Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the concentration of ammonium persulfate when forming a semiconductor layer was changed to 0.4 mol / l. The semiconductor layer at this time is
It was confirmed that the composition was composed of lead dioxide and lead sulfate, and contained about 35% by weight of lead dioxide.

Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that 0.05 mol / l of hydrogen peroxide solution was further added to the reaction mother liquor when forming the semiconductor layer. It was confirmed that the semiconductor layer at this time was a composition composed of lead dioxide and lead sulfate, and contained about 50% by weight of lead dioxide.

Example 4 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that 0.2 mol / l of hydrogen peroxide solution was further added to the reaction mother liquor when forming the semiconductor layer in Example 1.

It was confirmed that the semiconductor layer at this time was a composition composed of lead dioxide and lead sulfate, and contained about 94% by weight of lead dioxide.

Comparative Example 1 Using the same etched aluminum conversion foil as in Example 1, an electrolytic capacitor using an electrolytic solution was prepared by a method known in the art. That is, a wound element consisting of an anode foil (each having an etched aluminum conversion foil) with a terminal, a cathode foil and a separator is impregnated with an ethylene glycol ammonium adipate-based electrolytic solution, and the element is placed in an aluminum outer case. It was housed and the opening was closed with a rubber sealing body to fabricate an electrolytic capacitor.

Comparative Example 2 The same etched aluminum conversion foil as in Example 1 was used, and TCNQ was used according to the method described in JP-A-58-17609.
A solid electrolytic capacitor having a salt as a conductor layer was produced. That is, a complex salt of isopropylisoquinoline and TCNQ was placed in an aluminum outer case and heated and melted. Next, a wound element consisting of an anode foil, a cathode foil, and a separator, each having terminals, was preheated in advance and impregnated in the above-mentioned molten TCNQ complex salt, and quickly cooled and solidified. The opening was closed with a rubber sealing body to produce an electrolytic capacitor.

Comparative Example 3 Instead of using an aqueous solution having a lead acetate trihydrate concentration of 3.8 mol / l in Example 1, an aqueous lead citrate solution having a lead citrate concentration of 0.7 mol / l was used, and the ammonium persulfate concentration was changed. To 4.
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the reaction mother liquor adjusted to 8 mol / l was used. It was confirmed that the semiconductor layer at this time was a composition composed of lead dioxide and lead sulfate, and contained about 5% by weight of lead dioxide.

[Brief description of drawings]

FIG. 1 is a perspective view of a spirally wound anode valve metal substrate. 1 ... Anode valve metal substrate, 2 ... Anode lead terminal.

Claims (4)

[Claims] 1. A semiconductor layer containing lead dioxide and lead sulfate as main components and a conductor layer are sequentially formed on the oxide layer of a spirally wound anode valve metal substrate having an oxide layer on its surface. A solid electrolytic capacitor characterized in that 2. A semiconductor layer comprising lead dioxide and lead sulfate as main components, which is a layer chemically deposited from a reaction mother liquor containing lead ions and persulfate ions. Solid electrolytic capacitor. 3. The concentration of lead ions in the reaction mother liquor is 0.1 mol / l.
The solid electrolytic capacitor according to claim (2), wherein the solid electrolytic capacitor has a range of from 0.1 to 5 mol per 1 mol of lead ion, in a range from 1 to a concentration giving saturated solubility. 4. Lead dioxide in a semiconductor layer is 10% by weight or more and 10% by weight or more.
Claim (1) included in the range of less than 0% by weight
The solid electrolytic capacitor as described in the item.