WO2005119716A1

WO2005119716A1 - Sintered element for solid electrolytic capacitor, anodized element for solid electrolytic capacitor, solid electrolytic capacitor and method for manufacturing them

Info

Publication number: WO2005119716A1
Application number: PCT/JP2005/009741
Authority: WO
Inventors: Hiroaki Wada
Original assignee: Pure Material Laboratory Ltd.
Priority date: 2004-06-03
Filing date: 2005-05-27
Publication date: 2005-12-15
Also published as: JP4139354B2; JP2005347577A

Abstract

An anode which constitutes a capacitor is formed of a valve metal. The anode is converted into a conductive oxide by heat treatment after forming and sintering an element or after anodizing the element, and heat resistance of the anode against an excess voltage applied on the capacitor is improved. Thus, a sintered element for solid electrolytic capacitor and an anode element for solid electrolytic capacitor, which can improve withstand voltage of the solid electrolytic capacitor element without increasing element sizes nor deteriorating capacitance of the element, are provided. A solid electrolytic capacitor which uses these elements and has excellent withstand voltage and a method for manufacturing such elements and the capacitor are also provided.

Description

Specification

Sintered element for solid electrolytic capacitor, anodized element for solid electrolytic capacitor, solid electrolytic capacitor, and method for producing them

Technical field

The present invention relates to a sintered element for an electrolytic capacitor, which can improve the withstand voltage thereof without increasing the size of the electrolytic capacitor and without reducing its capacitance, The present invention relates to an anodizing element for a capacitor, an electrolytic capacitor having excellent withstand voltage using such an element, and a method for producing the same.

Background art

[0002] As is well known, a capacitor is used to store electricity in an electric circuit and an electronic circuit of many electric products and electronic products such as a mobile phone and a personal computer, or to interrupt a direct current and generate an alternating current. It is an important element used to serve the purpose of passing. The basic structure of a capacitor is shown as a structure in which a dielectric (insulator) is sandwiched between two electrodes. When a DC voltage is applied between the two electrodes, electricity called an electric charge is stored in each of the electrodes, and a current flows during storage, and stops flowing when storage is completed. A wide variety of materials are used for the electrodes and dielectrics, and the selection of these materials provides capacitors having unique advantages. Capacitors for electronic circuits include plastic film capacitors, ceramic capacitors, microcapacitors, aluminum electrolytic capacitors, tantalum solid electrolytic capacitors, and electric double layer capacitors.

[0003] Among the various capacitors, tantalum solid electrolytic capacitors are slightly more expensive than capacitors made of other materials, have extremely long service life, are small in size and have excellent high-frequency characteristics, and are compact digital devices such as mobile phones. It is a capacitor that is ideal for equipment, is currently in the spotlight, and is in high demand.

[0004] The solid electrolytic capacitor uses, as a positive electrode, a metal called a valve metal having a highly corrosion-resistant and insulating oxide film (passive film) formed on its surface by anodic oxidation. The oxide film is used as a dielectric, and a cathode material is formed on the anodic film. This is a capacitor using this as a cathode. Aluminum electrolytic capacitors and tantalum electrolytic capacitors are currently in practical use. Examples of the valve metal include aluminum, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Recently, trial production of a niobium electrolytic capacitor using niobium has started.

[0005] The aluminum electrolytic capacitor has a structure in which an electrolytic solution (cathode) impregnated in kraft paper or the like is sandwiched between metal aluminum foils on which an oxide film is formed and wound. In contrast, a tantalum solid electrolytic capacitor has a structure that utilizes the gap created when the metal tantalum powder is sintered and hardened, and can secure a high surface area. Excellent in frequency characteristics.

[0006] A tantalum solid electrolytic capacitor is formed by pressing a fine particle powder of tantalum (Ta) metal and sintering it in a vacuum at a high temperature. Forming a dielectric oxide film (tantalum pentoxide: TaO) layer having a thickness of about several tens of nanometers.

twenty five

It is used as a denser (Non-Patent Document 1).

[0007] The manufacturing process of the tantalum solid electrolytic capacitor is described in more detail as follows.

The tantalum metal powder is mixed with a compound such as camphor and granulated, filled into a mold, and a tantalum wire serving as an anode lead wire is inserted and press-molded. The molded article (molded bellet) volatilizes the binder and sinters the particles in a vacuum sintering furnace to obtain a very porous sintered element. FIG. 1 is a schematic cross-sectional view of the sintered element, and FIG. 2 is a scanning electron microscope (SEM) photograph of a fractured surface of the sintered element. As shown in FIG. 1, in the sintered element 1, the surfaces of the particles 2 of the tantalum metal powder and the particles 2 and the tantalum wire 3 are connected to each other as a result of their surfaces being melted. As a result, a complicated three-dimensional space 4 is formed inside the element 1. The three-dimensional space 4 has a very complicated structure, as is clear from the SEM photograph power of FIG. 2, and as a result, the surface area of the inner wall surface of the space 4 is enormous. The particles that make up the tantalum metal powder are actually composed of a single particle (called a primary particle) and a particle group formed by aggregating multiple particles (called a secondary particle). As a result, the three-dimensional space 4 in the sintered particles 1 has a complicated main road-like space and a branch-like space branched from it. It is composed of a three-dimensional continuous space combined with. As a result, as described later, it is possible to make the solution for forming the cathode formed in the internal space permeate into the details of the space. Further, each particle 2 has a complicated shape having many irregularities, rather than a circular shape as shown in the figure, thereby further complicating the internal space. That is, the surface area of the inner wall portion forming the three-dimensional internal space is very large.

[0008] Next, the porous sintered element is immersed in an electrolytic solution and anodized. As the electrolytic solution, a solution such as phosphoric acid, nitric acid, sulfuric acid, or various carboxylic acid solutions that can easily oxidize tantalum metal by applying a voltage is used. As shown in FIG. 3, the entire inner and outer surfaces of the tantalum sintered element 1 are completely oxidized by this anodic oxidation, so that

Two

O) A coating 5 is formed. This pentoxide film 5 is a passive film, and its thickness is

Five

Is determined by the voltage applied in this chemical conversion process, and a thickness of about 1.5 nm is formed per applied voltage IV. The anodized film 5 constitutes the dielectric of the capacitor, and the connected tantalum metal particles 2 constitute the anode, and are electrically drawn out by the tantalum wire 3. FIG. 4 shows a SEM photograph of a fractured surface of the anodized device. The sintered element that has been subjected to anodizing treatment so that the SEM photographic power also contributes has a structure in which an anodized film is formed outside and metal tantalum is wrapped inside.

A three-dimensional space having the anodized film 5 as an inner wall is filled with a cathode material to form a cathode 6. Manganese dioxide, polythiophene, polypropylene and the like are used as the cathode material. In the case of diacid manganese, dilute manganese nitrate Mn (NO) with water.

3 2 Firstly, dilute the hydrated salt or a thinner hydrated solution, immerse the sintered element (anode element) after forming the anodic oxide coating 5 in the aqueous solution, take out it, and remove it at 250 ° C. The firing at about 260 ° C. is repeated several times to several times several times to form a film of manganese dioxide (cathode 6).

[0010] A carbon layer 7 and a silver paste layer 8 are sequentially formed outside the cathode 6, and the cathode 6 is connected to a cathode terminal (not shown) via these layers.

[0011] In the tantalum solid electrolytic capacitor having the above configuration, niobium (Nb) is used instead of tantalum.

) Is a niobium solid electrolytic capacitor. In niobium solid electrolytic capacitors , Niobium is the anode, niobium pentoxide (NbO) coating is the dielectric, manganese dioxide

twenty five

Such a coating constitutes the cathode. In the niobium solid electrolytic capacitor having this configuration, the niobium Z interface is unstable, and good performance cannot be obtained. At present, in addition to niobium, an oxidized niobium solid electrolytic capacitor using a conductive niobium oxide (NbO) having a low oxygen number as an anode has been experimentally manufactured. It has been confirmed that the withstand voltage is improved by using niobium oxide as the anode (Patent Document 1, Non-Patent Documents 2 and 3).

[0012] In the tantalum solid electrolytic capacitor described above, when used in an electric circuit or an electronic circuit, an overvoltage such as a surge voltage or a back electromotive voltage when the circuit switch is turned on or off, or a high ripple voltage during use. If this occurs, the element will be burned due to the overvoltage, and in some cases, a fire may occur in the equipment.

[0013] The capacitor ideally has an infinite impedance during the application of a direct current, so that no current flows. However, in practice, the impedance does not become infinite even when a direct current is applied, and a current flows. This is the leakage current, which occurs at places where the anodic oxide coating is thin or where there are minute defects. Therefore, strict process control and quality control are required during the production of capacitors, and attention is paid to the formation of high quality anodized films.

However, in recent years, as the capacity of tantalum solid electrolytic capacitors has increased, the element powder has become finer, the specific surface area has increased, the anodized film has become thinner, and the withstand voltage of the film has been decreasing. It is in. For this reason, it has been pointed out that there is no allowance for the withstand voltage of the coating against the above-mentioned overvoltage, and the insulation of the coating is short-circuited, the electrical conduction path in the capacitor is short-circuited, and the burnout of the element may increase.

[0015] In response, the following three measures have been proposed and implemented.

(1) Use a fuse for the tantalum solid electrolytic capacitor. Such products include, for example, ROHM CO. LTD TCFGP / TCFGA / TCFGB

The series (product name) is known.

(2) Thin tantalum wires and leads of tantalum solid electrolytic capacitors (Non-Patent Document 4).

(3) The thickness of the anodized film is increased to increase the withstand voltage of the element (Non-Patent Document 5).

Patent Document 1: Japanese Patent Application Publication No. 2002-524378 Non-Patent Document 1: Atsushi Ihara, Akihiko Masuda "Latest Handbook of Electronic Components and Device Mounting Technologies" Published by: R & D Planning, published December 16, 2002

Non-Patent Document 2: “Comparison of Niobium and Niobium Oxide Solid Electrolytic Capacitors” CARTS 2003: 23rd Capacitor And Resistor Technology Symposium, March 31—April 3, 2003 Non-Patent Document 3: “Regarding the electrical performance of NbO-based electrolytic capacitor powder Role of synthesis and phase formation '' CARTS 2003: 23rd Capacitor AndResistor Technology Symposium, March 31- April 3, 2003

Non-Patent Document 4: Kazuyuki Kanemoto "Development of Open Mode Capacitors"

Published December 11, 2003

Non-Patent Document 5: “Voltage derating for solid tantalum and niobium capacitors; φ” ARTS 2003: 23rd Capacitor AndResistor Technology symposium, March 31—April 3, 2003

Disclosure of the invention

Problems to be solved by the invention

[0017] However, while the measures (1) and (2) described above can prevent a fire accident, the important function as a capacitor is lost, and electronic equipment incorporating the capacitor cannot be used. It becomes unusable. In addition, the method of (3) can be effective as a measure for preventing ignition, but the size of the element is increased, and if it cannot be used for electronic devices that require miniaturization, it will be less powerful. This leads to higher costs.

[0018] On the other hand, in the case of a solid electrolytic capacitor of niobium oxide, the anode has a relatively high flammability! Without using niobium metal (measured ignition temperature: 290 ° C), the conductive By using niobium (actual ignition temperature: 353 ° C), the withstand voltage of the element is improved. However, a new problem arises in a solid electrolytic capacitor of niobium oxide using this niobium as an anode. It is an unavoidable problem due to the manufacturing process. In the production of this niobium anilide solid electrolytic capacitor, first, as disclosed in Patent Document 1, a high-grade anilide (niobium) is reduced to a lower anilide. Form a slag of NbO suboxide. Next, the slag is sintered to obtain a sintered element. The obtained sintered element is subjected to anodizing treatment, and the surface of the element is coated with a niobium pentoxide niobium film ( (Dielectric film).

[0019] As described above, in a solid electrolytic capacitor of niobium oxide, an oxide is used for molding using a mold. The acid ridicule has high hardness and brittle characteristics. As a result, firstly, the mold is heavily worn and the life of the mold is shortened, resulting in an increase in manufacturing cost. Secondly, since the particles are brittle, not only the secondary particles but also the primary particles are broken at the time of molding, and a complicated shape is lost. As a result, the internal surface area of the three-dimensional space formed inside the molding element is significantly reduced as compared with the case where the metal niobium particles are molded. Therefore, although the element weight is the same, the capacitor capacity of the solid electrolytic capacitor of niobium oxide is smaller than that of the element formed of metal niobium particles.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid electrolytic capacitor element that does not increase the size of the element and does not reduce the capacitance of the element. It is an object of the present invention to provide a sintered element for a solid electrolytic capacitor capable of improving a voltage, an anode element for a solid electrolytic capacitor, a solid electrolytic capacitor using these elements and having excellent withstand voltage, and a method for producing the same.

Means for solving the problem

The present inventor has earnestly conducted experiments and studies to solve the above-described problems and achieve the object, and has obtained the following knowledge. The study to make it possible to improve the withstand voltage of the conventional solid electrolytic capacitor focused on the tantalum solid electrolytic capacitor, which is currently in the highest demand.

[0022] A tantalum solid electrolytic capacitor is manufactured through a number of steps as described above.

That is,

1. Adjustment of tantalum powder

2.Adjust by adding binder to powder

3.Press molding

4.vacuum sintering

5.Anodic oxidation

6. Addition of cathode surface and cathode terminal 7. Other processes

When the anodized element obtained in the step 5 is observed by SEM, the cross section of the sintered particles in the element is as shown in FIG. That is, amorphous tantalum pentoxide is formed by anodic oxidation on the outside of the sintered particles, and metal tantalum is formed on the inside thereof. When exposed to the above-mentioned overvoltage, which has a high reactivity with oxygen, the metal tantalum that functions as the anode generates heat and reacts with the surrounding oxygen to burn, causing fires in electronic equipment and other causes. .

[0024] Then, when the tantalum oxidized product was examined, the highly oxidized tantalum pentoxide was insulative and the oxidized tantalum pentoxide (Ta O and / or Ta O)

In the case of 42, the reactivity with oxygen was drastically reduced, and it was found that the force maintained the conductivity. The problem was whether the maintained conductivity satisfies sufficient conductivity as the anode of the device, but actual measurements confirmed that there were no problems. While such lower oxides have significantly reduced reactivity with oxygen, they maintain conductivity and can be used for filling as an anode, as described above. The present inventors have further investigated tantalum in solid electrolytic capacitors using niobium, and found that further improvements were necessary in using the conductive oxide. I came to know.

[0025] When a lower oxide of tantalum is used for the anode, as in the case of niobium described above, the raw material tantalum powder is changed to a conductive oxide, and the oxide powder is formed and sintered. First, a method was conceived in which the obtained oxide sintered body was subjected to anodizing treatment to obtain a conductive oxide sintered element having a tantalum pentoxide film formed on the surface.

[0026] While the tantalum powder is being oxidized to a low degree, the conductive oxide (Ta O or

4 Z and Ta O) to form the oxide particles and then sinter to obtain an oxide sintered element

2

In the method, first, the powder is easily broken at the time of molding, and a metal tantalum powder tends to have a complicated shape, whereas an oxide powder tends to have a relatively simple shape. Therefore, the specific surface area of the molded element is reduced, and the capacitance value of the capacitor is reduced. In addition, in the case of metal tantalum powder, each particle has a complicated uneven shape, and the particles are connected while maintaining many voids by a so-called fastener effect. Thus, the effect of increasing the three-dimensional space of the molded body, maintaining a complicated uneven shape, and maintaining a large surface area could be obtained. On the other hand, when the oxide powder is formed, the particles are broken into a simple shape, so that the fastener effect is significantly reduced and the formability is deteriorated. It is necessary to use a binder. It was also confirmed that the use of a strong binder caused the binder to remain as a carbon component even after sintering in a vacuum heating furnace, immediately affecting the electrical characteristics of the capacitor.

[0027] On the other hand, a metal tantalum powder is molded, the obtained molded element is sintered to form a sintered element, and the sintered element is subjected to a heat treatment, and the entire element is made of a conductive oxide. Was considered. As a result, at the heat treatment at this stage, the shape of the metal tantalum particles constituting the molded element was not broken, so that the capacitance value of the obtained capacitor did not decrease. The entire element is made of conductive oxide (Ta O or

4 or Z and TaO, so in the next anodic oxidation process

The transport amount of oxygen for forming the 2 2 5 oxidized oxide film depends on the surface of the metal tantalum particles.

The current efficiency of anodic oxidation is improved because it may be smaller than in the case of 25. In addition, thermal distortion and micro-cracks generated in the metal tantalum particles constituting the element by this heat treatment are eliminated during the subsequent anodic oxidation, and a stable anodic oxidation film can be formed. In addition, when forming each particle of the metal tantalum powder without breaking the complicated uneven shape, a fastener effect of the particles can be obtained, so that the binder amount can be reduced. Further, at the time of oxidation by heat treatment, oxygen has an effect of purifying the device by reacting with residual impurities in the device. In particular, it is effective in removing the residual carbon of the binder added during the preparation of the tantalum powder. As a result, the anodic oxide film is electrically stabilized as compared with the case of the normal treatment, and the electric characteristics such as leakage current are improved.

Next, a metal tantalum is formed and sintered to obtain a sintered element, and the obtained sintered element is subjected to anodizing treatment, so that the surface of the metal tantalum is anodized. An anodized element having a tantalum film formed thereon was obtained. Heat treatment was performed on this anodized element, and the case where the metal tantalum inside the anodized film was used as a conductive oxide was examined. As a result, first, in the heat treatment at this stage, the anodic oxide film is stabilized by the aging effect of this heat treatment. That was confirmed. However, another factor was the possibility of heat distortion and micro-cracking in a part of the anodic oxide coating. On the other hand, it was confirmed that re-anodizing treatment after the heat treatment alleviated the thermal strain and repaired the micro cracks that occurred. Also in this case, during the heat treatment, oxygen has the effect of reacting with residual impurities in the device to purify the device. In particular, it is effective for removing the residual carbon of the binder added at the time of forming the element. As a result, the anodized film is electrically stable and has improved electric characteristics such as leakage current, as compared with the case of the normal treatment.

[0029] The iridescence by these heat treatments can be achieved by controlling the heat treatment conditions as follows.

That is, tantalum metal is converted to the desired conductive oxide TaO or Z and TaO

In order to obtain 42, the sintered element before anodizing or the anodizing element after anodizing is heat-treated in an electric furnace. The heat treatment conditions are different in each case.The heating temperature is 200 ° C to 500 ° C, the heating time is 10 minutes to 10 hours, and the oxygen concentration in the atmosphere is 5% to 50%. Inject while controlling argon gas or nitrogen gas.

[0030] The present invention has been made based on the above findings. That is, the sintered element for a solid electrolytic capacitor according to the present invention is formed by sintering the conductive oxide particles of the valve metal in a state of being formed into a predetermined shape, thereby forming the conductive oxide particles. It is characterized in that the primary and secondary particles maintain the same complex asperities as the primary and secondary particles when the non-oxidized valve metal particles are molded and sintered.

In the anodic oxidation element for a solid electrolytic capacitor according to the present invention, the conductive oxide particles of the valve metal are sintered in a state of being formed into a predetermined shape, and the surface of the sintered particles is insulated. The primary oxide and secondary particles constituting the acidic oxide particles are formed into non-oxidized valve metal particles, and are the same as the primary particles and secondary particles when sintered. Characterized by maintaining a complicated uneven shape.

Further, the solid electrolytic capacitor according to the present invention is characterized in that the conductive oxide particles of the valve metal are sintered in a state of being formed into a predetermined shape, and the surface of the sintered particles has an insulating oxide particle. A conductive film is further formed on the surface of the insulating oxide, and the conductive oxide particles are connected by sintering to form an anode. Coating A capacitor structure is formed by forming a dielectric and further, the conductive film forms a cathode, and the primary particles and the secondary particles forming the oxide particles are non-oxidized valve metal particles. It is characterized by maintaining the same complex asperities as primary and secondary particles when molded and sintered.

[0033] Further, in the method for manufacturing a sintered element for a solid electrolytic capacitor according to the present invention, the valve metal particles are formed into a predetermined shape, and then sintered to form a sintered element. Then, the conductive oxide is used to obtain a sintered element for a solid electrolytic capacitor.

[0034] The heat treatment is preferably performed in an atmosphere having an oxygen concentration of 5% to 50%, at a heating temperature of 200 ° C to 500 ° C, and for a heating time of 10 minutes to 10 hours.

[0035] Further, in the method for producing an anodized element for a solid electrolytic capacitor according to the present invention, the valve metal particles are formed into a predetermined shape, and then sintered to form a sintered element. An anodizing treatment is performed to form an insulating oxide film on the surface of the sintered element, and the obtained anodizing element is heat-treated so that the valve metal particles covered with the insulating oxide film are conductively oxidized. In this case, an anodic oxidation element for a solid electrolytic capacitor is obtained.

[0036] The heat treatment is preferably performed in an atmosphere having an oxygen concentration of 5% to 50% at a heating temperature of 200 ° C to 500 ° C and a heating time of 10 minutes to 10 hours.

[0037] After forming the conductive oxide by the heat treatment, it is preferable to further perform anodization again. The conditions of the re-anodizing treatment in this post-treatment are as follows: a constant current of a constant current value is 1 minute to 60 minutes, and preferably, a constant voltage of a constant voltage value is followed by 1 hour to 8 hours. That is. The application time at the constant current is more preferably 2 minutes to 20 minutes. The application time at the constant voltage is preferably 1 hour to 5 hours.

[0038] Further, in the method for manufacturing a solid electrolytic capacitor according to the present invention, the valve metal particles are formed into a predetermined shape, and then sintered to form a sintered element. A sintered element is formed by forming an oxide film, and the sintered element is subjected to anodizing treatment to form an insulating oxide film on the surface of the sintered element. A conductive oxide film is formed, the insulating oxide film is used as a dielectric, the conductive oxide inside the dielectric acts as an anode, and the conductive oxide film outside the dielectric serves as a cathode. And a capacitor structure that functions as follows.

[0039] Further, in another method of manufacturing the solid electrolytic capacitor according to the present invention, the valve metal particles are formed into a predetermined shape, and then sintered to form a sintered element, and the obtained sintered element is subjected to anodizing treatment. To form an insulating oxide film on the surface of the sintered element, and heat treating the obtained anodic oxide element to make the valve metal particles covered with the insulating oxide film conductive. An anodized element is formed by converting it to an oxide, a conductive oxide film is formed on the surface of the insulating oxide film of the anodized element, and the insulating oxide film is used as a dielectric. It is characterized in that a capacitor structure in which an inner conductive oxide acts as an anode and an outer conductive oxide film of the dielectric acts as a cathode.

[0040] In each of the manufacturing methods of the solid electrolytic capacitor, the heat treatment is performed under the conditions of an oxygen concentration of 5% to 50%, a heating temperature of 200 ° C to 500 ° C, and a heating time of 10 minutes to 10 hours. It is preferred that

[0041] After the conductive oxide is formed by the heat treatment, it is preferable to perform anodization again. The conditions of the re-anodizing treatment in this post-treatment are as follows: a constant current of a constant current value is 1 minute to 60 minutes, and preferably, a constant voltage of a constant voltage value is followed by 1 hour to 8 hours. That is. The application time at the constant current is more preferably 2 minutes to 20 minutes. The application time at the constant voltage is preferably 1 hour to 5 hours.

[0042] In each of the manufacturing methods of the solid electrolytic capacitor, as the valve metal, tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium can be used, and tantalum and niobium are more preferable.

The invention's effect

[0043] By using the sintered element and the anodized element for a solid electrolytic capacitor according to the present invention, the heat resistance of the solid electrolytic capacitor can be remarkably improved, and even when an overvoltage is applied. In addition, it is possible to make burning harder than ever. Further, it is possible to significantly reduce the residual carbon in the element of the solid electrolytic capacitor. Also, it is possible to reduce the leakage current of the solid electrolytic capacitor. Further, according to the production method of the present invention, a stable solid electrolytic capacitor having extremely high thermal stability can be provided. Brief Description of Drawings

FIG. 1 is a schematic cross-sectional structure diagram of a sintered element for a tantalum solid electrolytic capacitor.

FIG. 2 is an SEM photograph of a fractured surface of a sintered element for a tantalum solid electrolytic capacitor.

FIG. 3 is a schematic cross-sectional structure diagram of an anodizing element for a tantalum solid electrolytic capacitor.

FIG. 4 is an SEM photograph of a fractured surface of an anodizing element for a tantalum solid electrolytic capacitor.

FIG. 5 is an X-ray diffraction chart of sintered particles when a sintered element is heat-treated, for explaining the example of the present invention.

FIG. 6 is an X-ray diffraction chart of internal components of sintered particles when an anodizing element is subjected to a heat treatment, for explaining an example of the present invention.

FIG. 7 is a chart showing a low intensity region of the X-ray diffraction chart shown in FIG. 6. Explanation of symbols

[0045] 1 Sintered element

2 Sintered particles

3 Tantanore wire

4 Three-dimensional space inside sintered element

5 Anodized film

6 Cathode

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, examples of the present invention will be described. It should be noted that the following examples are merely examples for suitably describing the present invention, and do not limit the present invention in any way.

Example

The following embodiment is an example in which tantalum is used as a valve metal. The average particle size of the tantalum metal powder used was 0.6 m. (Experiment method)

The sintered element used in the experiment was manufactured by pressing a tantalum metal powder using a mold and sintering at 1400 ° C for 20 minutes. The size of the sintered element 1. Omm X 3. 3mm X 3. 5mm , density after sintering is about one third of the true density 5. 5gZcm ^3, specific surface area meet 0. 6 m ² / g Was.

[0049] The anodizing treatment is carried out in a phosphoric acid aqueous solution having a concentration of lwt% at 60 ° C and a constant current of 35 mA / g (58 mA / m ² ) at a constant current of about 5 hours until it reaches 40 V. , And 40 V—maintained at a constant voltage for 2 hours to obtain an anodized element.

Conductive oxide (Ta O or

4 Z and Ta O)

2

The sintered element (sintered element before anodization) and the anodized element (sintered element after anodization)

) Was performed in the air and used for measuring electrical characteristics.

[0050] In the case where the sintered element is subjected to heat treatment to form a conductive oxide, the heat treatment conditions include (i) no heat treatment, (ii) 300 ° C for 1 hour, (iii) 350 ° C for 1 hour, (iv) 350 ° C x 4 hours,

(v) 350 ° C × 9 hours.

On the other hand, when heat treatment was performed on the anodized element to make the inside of the particles a conductive oxide, the heat treatment conditions were (i) 400 ° C. for 30 minutes and (ii) 450 ° C. for 30 minutes.

The measurement of the electric characteristics was performed in an electrolytic solution by a wet method. The re- (post-treatment) anodization was performed for 5 minutes at a constant current of the same current density as that of the first (main treatment) anodization, and then performed at a constant voltage of the same voltage as that of the first (main treatment) anodization. Hold for hours.

[0052] The formation of the conductive oxide by the heat treatment was confirmed by subjecting the heat-treated tantalum metal portion to X-ray diffraction and identifying the obtained peak. The X-ray diffraction device used was MXP18VAHF (product number) manufactured by Mac Science, Inc. of the United States, and the X-ray output was

It was 40 kV x 300 mA and CuKa wire was used.

In order to evaluate the heat resistance of each of the obtained devices, the ignition temperature was measured. The force was measured by a glow-wire flammability tester (Model G, manufactured by Suga Test Instruments Co., Ltd.).

W-1) was used.

[0054] (Evaluation)

As mentioned above, confirmation of the formation of conductive oxides (Ta 0, Ta O) by heat treatment It was done by folding. X-ray diffraction charts of the internal components of the particles of each sample obtained by the heat treatment under the respective heat treatment conditions of the sintered element and the anodized element are shown in FIGS.

[0055] The chart in Fig. 5 is an X-ray diffraction chart when the sintered element is subjected to a heat treatment. In the chart, the curve indicated by A is the peak line of (i) the X-ray diffraction of the sample without heat treatment, and the curve indicated by B is (ii) the X-ray of the sample heat-treated at 300 ° C for 1 hour. The peak line of X-ray diffraction, the curve indicated by C is (iii) the peak line of X-ray diffraction of the heat-treated sample at 350 ° C X l hours, and the curve indicated by D is (iv) X of the heat-treated sample at 350 ° CX for 4 hours. The curve indicated by E, the peak line of X-ray diffraction, is the peak line of (V) X-ray diffraction of the heat-treated sample at 350 ° C for 9 hours. Vertical lines displayed at the bottom of these peak curves over three levels are Ta, Ta 0,

Four

The Ta O peak position is shown.

2

As can be seen from these peak curve forces, conductive oxides began to form in samples after heat treatment at 300 ° C for 1 hour (curve B) and heat treated at 350 ° C for 4 hours (curve D). In most cases, the conductive oxidized product was a conductive oxidized product, and it was confirmed that all of the particle components were replaced with the conductive oxidized product in the heat-treated product at 350 ° C for 9 hours (curve E).

[0056] The chart in Fig. 6 is an X-ray diffraction chart when a heat treatment is applied to the anodized element. In the chart, the curve indicated by W is the peak line of X-ray diffraction of the sintered element sample without heat treatment, and the curve indicated by X was obtained by performing anodizing treatment of the sintered element at 40VX for 2 hours. The peak line of the X-ray diffraction of the anodized device sample and the curve indicated by Y are (i) the peak line of the X-ray diffraction of the sample obtained by subjecting the anodized device to a heat treatment at 400 ° C. for 30 minutes; The curve shown is (ii) the peak line of X-ray diffraction of the sample obtained by subjecting the anodized element to heat treatment at 450 ° C. for 30 minutes. Vertical lines displayed in three steps below these peak curves indicate the peak positions of Ta, Ta0, and TaO, respectively.

4 2

The conductive oxide was formed in the samples after the heat treatment at 400 ° C. for 30 minutes (curve Y) after the anodizing treatment at 40 V × 2 hours so that these peak curve forces also contributed. It has been confirmed that, after anodizing at 40VX for 2 hours, the heat treatment product at 450 ° C for 30 minutes (curve Z) further replaced all of the inside of the particles with conductive oxide.

FIG. 7 is a chart in which the diffraction angle 2 ° of the curves W and Z is enlarged in the vicinity of 10 degrees to 50 degrees. It is. It can be confirmed that a broad peak appears at a diffraction angle 20 of curve Z of 20 degrees to 35 degrees. This is a peak peculiar to the anodized film, and is observed in the curves X and Y. Since the peak is not a sharp peak but appears broad, it may be an amorphous film. You can check. In this curve Z, as in the case of curves X and Y, it can be confirmed that the anodized film is amorphous. This means that the anodized film can be crystallized even after further heat treatment after the anodizing treatment. This indicates that the heat treatment employed in the present invention does not cause deterioration of the anodized film.

Next, according to the identification by the X-ray diffraction, the sintered element sample in which the particles of the sintered element are completely conductive oxide (curve E) and the inside of the particles of the anodized element were completely removed. The anodized sample (curve Z), which is a conductive oxidized product, was evaluated as an evaluation sample II, and heat resistance (ignitability), residual carbon content, electric characteristics (leakage current, capacitance , Equivalent series resistance). The results are shown in Table 1 below. For comparison, various characteristics of the anodized element without heat treatment represented by the curve W as the sample I were measured, and also shown in Table 1. Note that the characteristic values shown in Table 1 are for one sintered element.

[0059] The measured values of the ignition temperature shown in Table 1 are the ignition temperatures obtained by external ignition. In the anodized element, a passivation film (Ta O) is formed on the surface of the sintered particles.

twenty five

Therefore, when igniting from the outside, the passive body coating protects the inside and the accurate evaluation cannot be performed. Therefore, the ignition temperature when the inside of the sintered particles of the anodized element is metal tantalum, and the ignition temperature when the conductive oxide such as TaO or TaO is used.

4 2

In the former, the pellets obtained by molding and sintering metal tantalum particles were used as sample I.

In the latter case, pellets formed and sintered of Ta 2 O particles were used as samples II and III.

Four

[Table 1] (Table 1) Value per sintered element

[0061] (heat resistance)

As shown in Table 1, the conventional sintered device (Sample I) was a device in which the entire device was made of conductive oxide TaO or TaO force by heat treatment ignited at 375 ° C (Samples II and III).

4 2

The ignition temperature increased significantly to 545 ° C. That is, the heat resistance was significantly improved.

In other words, usually, the central part of the sintered particles of the anodized element is metal tantalum. This is converted into a tantalum conductive acid TaO or TaO to form a capacitor.

4 2

The ignition temperature of the tantalum sintered element incorporated in the device increased from 375 ° C to 545 ° C, confirming that the heat resistance was significantly improved.

As described above, the measured ignition temperature of NbO is 353 ° C, and the measured ignition temperature of Nb is 290 ° C. On the other hand, the ignition temperature of Ta is 375 ° C, and when it is Ta O or TaO which is a conductive oxide, the ignition temperature is 545 ° C. Therefore, at least heat resistant

4 2

Tantalum oxide solid electrolytic capacitors are superior to niobium oxide solid electrolytic capacitors from the viewpoints of performance and ヽぅ.

[0062] (Residual carbon amount)

As shown in Table 1, the carbon content was 1170 at ppm for the normal treatment (conventional product). The sintered element before the anodization was heat-treated at 350 ° C for 9 hours (sample II). 610 At ppm, it decreased to 750 at ppm in the anodized device after heat treatment at 450 ° C for 30 minutes (Sample III).

(Electrical characteristics: leakage current, capacitance, equivalent series resistance)

In the research on solid electrolytic capacitors, the usual measurement of electrical characteristics was performed by anodizing, drying at 100 ° C for 30 minutes, and then wet in an electrolytic solution. Table 1 shows the electrical properties of the conventional product (sample I) and the product of the present invention (samples II and III) which were normally treated. The leakage current is 1.41 A in the conventional product (Sample I). It is 1.21 / ζ ζ in Sample II, which is the product of the present invention, and 0.83 A in Sample III, which is greatly improved. .

Further, the capacitance and the equivalent series resistance were almost the same value among the three.

[0064] In the above embodiment, the solid electrolytic capacitor in the case where tantalum is used as a valve metal is described. The present invention is also applied to valve metals that may constitute other solid electrolytic capacitors such as niobium. It is clear that the present invention is similarly applicable, and in that case, the same operation and effect can be obtained.

Industrial applicability

As described above, according to the present invention, in solid electrolytic capacitors such as a tantalum solid electrolytic capacitor, the heat resistance can be remarkably improved, and even when an overvoltage is applied, the solid electrolytic capacitor is compared with the conventional one. It is possible to make it extremely difficult to burn. Furthermore, it is possible to greatly reduce the residual carbon in the elements of the solid electrolytic capacitor. It is also possible to reduce the leakage current of the solid electrolytic capacitor. Further, according to the manufacturing method of the present invention, a stable solid electrolytic capacitor having extremely high thermal stability can be provided.

Claims

The scope of the claims

[1] The conductive oxide particles of the valve metal are sintered in a state of being formed into a predetermined shape, and the primary particles and the secondary particles constituting the conductive oxide particles are in a non-oxidized state. A sintered element for a solid electrolytic capacitor, characterized by maintaining the same complex asperities as primary and secondary particles when valve metal particles are formed and sintered.

2. The sintered element for a solid electrolytic capacitor according to claim 1, wherein the valve metal is one selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

[3] The conductive oxide particles of the valve metal are sintered in a state of being formed into a predetermined shape, and an insulating oxide is formed on the surface of the sintered particles. The primary and secondary particles that constitute the non-oxidized valve metal particles maintain and maintain the same complex irregularities as the primary and secondary particles when molded and sintered. Anodizing element for solid electrolytic capacitors.

4. The anodic oxidation device for a solid electrolytic capacitor according to claim 3, wherein the valve metal is one selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

[5] The conductive oxide particles of the valve metal are sintered in a state of being formed into a predetermined shape, and an insulating oxide is formed on the surface of the sintered particles. A conductive film is further formed on the surface, the conductive oxide particles connected by the sintering constitute an anode, the insulating oxide film forms a dielectric, and the conductive oxide particles further form a dielectric. When the coating forms the cathode, a capacitor structure is formed, and the primary particles and the secondary particles constituting the oxide particles form primary particles and the secondary particles when non-oxidized valve metal particles are molded and sintered. A solid electrolytic capacitor characterized by maintaining the same complex asperities as secondary particles.

6. The solid electrolytic capacitor according to claim 5, wherein the valve metal is one selected from tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

[7] After molding the valve metal particles into a predetermined shape, sintering is performed to obtain a sintered element. A method for producing a sintered element for a solid electrolytic capacitor, characterized in that a sintered element for a solid electrolytic capacitor is obtained by heat-treating a conductor to form a conductive oxide.

[8] The heat treatment is performed in an atmosphere having an oxygen concentration of 5% to 50%, a heating temperature of 200 ° C to 500 ° C, and a heating time of 10 minutes to 10 hours. Item 7. The method for producing a sintered element for a solid electrolytic capacitor described in Item 7.

[9] The method for producing a sintered element for a solid electrolytic capacitor according to claim 7, wherein the valve metal is one selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

[10] After molding the valve metal particles into a predetermined shape, sintering is performed to obtain a sintered element, and the obtained sintered element is subjected to anodizing treatment to form an insulating oxide film on the surface of the sintered element. The anodized element for a solid electrolytic capacitor is formed by heat-treating the obtained anodized element to form a conductive oxide from the valve metal particles covered with the insulating oxide film. A method for producing an anodic oxidation element for a solid electrolytic capacitor, characterized by being obtained.

[11] The heat treatment is performed in an atmosphere having an oxygen concentration of 5% to 50%, a heating temperature of 200 ° C to 500 ° C, and a heating time of 10 minutes to 10 hours. Item 11. The method for producing an anodizing element for a solid electrolytic capacitor according to Item 10.

12. The method according to claim 10, wherein the valve metal is one selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

13. The method for producing an anodized element for a solid electrolytic capacitor according to claim 10, wherein a re-anodizing treatment is performed after the conductive oxide is formed by the heat treatment.

14. The method for producing an anodized element for a solid electrolytic capacitor according to claim 13, wherein the condition of the re-anodizing treatment in the post-treatment is at least a constant current of 1 minute to 60 minutes.

[15] After molding the valve metal particles into a predetermined shape, sintering is performed to obtain a sintered element, and the obtained sintered element is heat-treated to form a conductive oxide, thereby forming a sintered element. The sintered element is subjected to anodizing treatment to form an insulating oxide film on the surface of the sintered element, a conductive oxide film is formed on the surface of the insulating oxide film, and the insulating oxide film is formed. As a dielectric A solid electrolytic capacitor comprising a capacitor structure in which a conductive oxide inside the dielectric acts as an anode and a conductive oxide film outside the dielectric acts as a cathode. Manufacturing method.

[16] The heat treatment is performed in an atmosphere having an oxygen concentration of 5% to 50%, a heating temperature of 200 ° C to 500 ° C, and a heating time of 10 minutes to 10 hours. Item 16. The method for producing a solid electrolytic capacitor according to Item 15.

17. The method for producing a solid electrolytic capacitor according to claim 15, wherein the valve metal is a kind selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

[18] After molding the valve metal particles into a predetermined shape, sintering is performed to obtain a sintered element, and the obtained sintered element is subjected to anodizing treatment to form an insulating oxide film on the surface of the sintered element. The anodic oxidation element is formed by heat-treating the obtained anodized element to convert the valve metal particles covered with the insulating oxide film into a conductive oxide, thereby forming an anodized element. A conductive oxide film is formed on the surface of the insulating oxide film of the device, the insulating oxide film is used as a dielectric, and the conductive oxide inside the dielectric serves as an anode, and the dielectric oxide serves as an anode. A method for producing a solid electrolytic capacitor, characterized in that a conductive oxide film on the outside of the above constitutes a capacitor structure that functions as a cathode.

[19] The heat treatment is performed in an atmosphere having an oxygen concentration of 5% to 50%, a heating temperature of 200 ° C to 500 ° C, and a heating time of 10 minutes to 10 hours. Item 19. The method for producing a solid electrolytic capacitor according to Item 18.

20. The method for manufacturing a solid electrolytic capacitor according to claim 18, wherein the valve metal is a kind selected from the group consisting of tantalum, vanadium, niobium, titanium, tungsten, hafnium, and zirconium.

21. The method for producing a solid electrolytic capacitor according to claim 18, wherein a re-anodizing treatment is performed after the conductive oxide is formed by the heat treatment.

22. The method for manufacturing a solid electrolytic capacitor according to claim 21, wherein the re-anodizing treatment condition of the post-treatment is at least a constant current of 1 minute to 60 minutes.