JP4604946B2 - Method for producing porous metal sintered body - Google Patents

Description

  The present invention relates to a method for producing a porous metal sintered body that can be suitably used for gas filter members, battery separators, non-ferrous metal casting molds, capacitor elements, and the like.

  In recent years, the technology of parts in electronic devices such as mobile phones, personal computers, digital cameras, etc. has dramatically improved. Under such circumstances, porous metal sintered bodies are used in various fields. For example, a porous nickel plate is used for a positive electrode of a nickel metal hydride battery, a porous metal sintered body is used for a capacitor element, and its large surface area is utilized. Also in other fields, for example, hollow metal porous bodies formed from flat metal powder are used for gas filter members. Porous metal molds are used for casting molds such as low pressure casting and die casting.

These porous metal sintered bodies are, for example, formed by mixing metal powder or metal granulated powder granulated using metal powder and resin and, if necessary, a binder resin to form a mixture. It is manufactured by firing a molded body obtained by press molding. Alternatively, it is manufactured by kneading a mixture containing metal powder and a binder resin to form a kneaded product, and firing a molded body obtained by molding the kneaded product.
For example, an organic acid ester is added to a metal powder and kneaded, and then an alkaline water-soluble phenol resin is added and kneaded. The resulting mixture is molded into a mold shape and molded in a vacuum or in an inert atmosphere. A manufacturing method for firing a body is disclosed (see Patent Document 1).
Also, after mixing nickel fine powder into a thermoplastic resin such as polyethylene, and then extruding and producing short fibers by irradiating with ultraviolet rays, the short fibers and water, a packing agent, a binder, and a dispersing agent Is formed into a green tape, degreased in a reducing atmosphere, and sintered to produce a metal porous plate (see Patent Document 2).
Also disclosed is a manufacturing method in which a paste containing fine particles of tantalum metal, a binder, and an easily sinterable metal is applied to a substrate and sintered in a vacuum or in an inert atmosphere, and then the sinterable metal is eluted and removed. (See Patent Document 3).

In such a porous metal sintered body, it is often important to increase the porosity in order to improve the characteristics in each application. Since the surface area of the porous body is improved by increasing the porosity, the number of functional parts increases in applications such as nickel porous plates, tantalum electrolytic capacitor anode elements, and catalysts used for the positive electrode of nickel metal hydride batteries. Thus, the characteristics are improved. Moreover, in a filter or an oil-impregnated bearing, good characteristics can be obtained by forming a porous body having a high porosity in which a large number of communication holes are formed.
The pores of the porous body are generated in a space where a small gap formed between the metal powders or a resin as a binder disappears and is removed. In order to increase the porosity, it is conceivable to reduce the density of the metal powder and prepare a sintered compact containing a large amount of binder. However, the shape of the compact is damaged in the process of disappearing the binder. It is difficult to obtain a sintered body having a structure.
In particular, when the particle size of the metal powder constituting the porous body is reduced in order to improve the surface area of the porous body, the pores are clogged and it becomes impossible to secure an effective pore volume. There was a thing. In addition, the binder may not be completely lost and may remain as a carbon residue in the sintered body.

In order to solve such problems and produce a porous metal sintered body having a high porosity, fine particles for forming pores are contained in the sintered compact, and stable voids are formed by the disappearance of the fine particles. The formation of holes is performed. For example, when forming an anode body of a tantalum electrolytic capacitor, by using a powder obtained by mixing 50 to 200 μm of valve action metal granulated powder and a solid organic substance having an average particle diameter of 20 μm or less as a material, The manufacturing method which increases a void | hole and a space | gap is disclosed (refer patent document 4). In this manufacturing method, it is said that by eliminating solid organic matter during sintering of the molded body, pores are formed in the porous metal sintered body and the penetration of the electrolyte solution for forming the cathode is facilitated. Examples of solids (hole forming materials) include polyvinyl alcohol organic solids, acrylic organic solids, and camphor.
However, since the disappearance and removal of the binder and the solid organic matter by heating proceed almost simultaneously, the outer wall forming the pores is likely to be damaged, and the shape of the sintered compact or sintered body is maintained while maintaining the shape. It was difficult to increase the porosity. In particular, camphor disappears prior to the binder and can be removed, but it is difficult to reduce the particle size, and it cannot be used to form pores with a fine pore size of 10 μm or less. There wasn't.

For this reason, attempts have been made to form stable pores by making a difference between the disappearance temperature of the hole forming material and the binder, and using a space forming material having a decomposition start temperature higher than the decomposition start temperature of the binder, It has been studied to obtain a porous sintered body through a first step of removing and a second step of removing a pore forming material to obtain a sintered body (see Patent Document 5). However, there has been a problem that the molded body from which the binder has been removed is liable to be damaged by the generation of a large amount of gas accompanying the decomposition of the pore forming material in the second step.
Furthermore, a method has been proposed in which resin particles that are pore forming bodies are selectively extracted with a solvent, and then the binder is heated and degreased (see Patent Document 6). However, when the particle size of the resin particles is small, it is difficult to allow the solvent to penetrate into the porous details. Therefore, the extraction operation takes time and it is difficult to completely remove the resin particles. It was.
As described above, it is not easy to form a stable sintered body having a large porosity, and in particular when the metal powder has a small particle size, it has a sufficient amount of pores and has shape stability. It was difficult to produce an excellent sintered body.

As a specific example, in a porous metal sintered body of tantalum metal used for a tantalum electrolytic capacitor anode element, tantalum metal powder mixed with a binder resin is molded with a predetermined mold, sintered, and then primary particles. A certain porosity was secured by forming pores between secondary particles formed by agglomeration. In order to further reduce the size and increase the capacity of the tantalum electrolytic capacitor, it is necessary to increase the surface area of the porous metal sintered body. Therefore, the particle diameter of the tantalum metal powder constituting the porous metal sintered body must be reduced. Considerations are being made.
However, when the particle size of the tantalum metal powder is reduced, not only does it melt at a relatively low temperature and the vacancies are easily crushed, but the cohesive force between the particles in the secondary particles is reduced and the secondary particles are liable to collapse. For this reason, the pores are crushed after the mold is formed, and it becomes difficult to form a porous body. Moreover, since the pores formed in the gaps between the secondary particles have a larger pore diameter than the pores formed in the gaps between the primary particles, when the secondary particles collapse, the electrolyte solution for forming the cathode is put into the sintered body. Sufficient voids for penetration are not formed. For this reason, in a tantalum electrolytic capacitor, if the particle size of the tantalum metal powder is reduced to increase the hole area and increase the capacitance, the capacitance extraction rate does not improve and the performance of the capacitor is sufficiently improved. It cannot be improved.
In particular, when a small tantalum metal powder having a CV value of 10 kCV or more is used, an electrolytic capacitor having a capacitance sufficiently corresponding to the characteristics of the tantalum metal powder cannot be manufactured.
JP 2000-42688 A JP 2000-54005 A JP-A-2-254108 JP-A-11-181505 JP 20012711101 A JP 2004-43932 A

An object of the present invention is a production method capable of stably producing a porous metal sintered body having a large porosity, and in particular, a high porosity is formed by the distribution of a large number of pores having a small volume. Another object of the present invention is to provide a production method for stably producing a porous metal sintered body.
In particular, the object of the present invention is to produce a porous metal sintered body having a high porosity even when a valve metal having a small primary particle size is used for high capacity, and the electrolyte solution penetrates. It is an object of the present invention to provide a method for producing a porous metal sintered body for an anode element for an electrolytic capacitor that can be easily surface-treated.

The method for producing a porous metal sintered body according to claim 1 of the present invention forms a molded body containing metal powder, a pore-forming material, and a binder resin, and the molded body has a temperature higher than the decomposition temperature of the pore-forming material. In the method for producing a porous metal sintered body in which the pore-forming material is pyrolyzed by heating and then sintered at a sintering temperature higher than this, the pore-forming material is a microbial cell. It is characterized by being particles of polyhydroxyalkanoate produced therein.
In the method for producing a sintered porous metal according to the present invention, the molded body is formed by applying or printing a metal powder dispersion containing metal powder, a pore forming material, a binder resin and a solvent on a substrate. Then, the substrate may be formed by peeling the substrate from the coated or printed material. By passing through such a coating or printing process, a thin molded body can be formed, and a sheet-like porous metal sintered body can be easily produced.
In the method for producing a sintered porous metal according to the present invention, the metal powder may be a valve metal. In this case, it is preferable that the CV value is 100 kCV or more because the effect of the present invention is remarkable.
In the method for producing a sintered porous metal according to the present invention, the valve metal may be tantalum. Moreover, in the manufacturing method of the porous metal sintered body of this invention, you may sinter after providing a lead | read | reed to the said molded object .

According to the method for producing a sintered porous metal of the present invention, since the produced polyhydroxyalkanoate microparticles produced in the cells of microorganisms are used as the pore forming material, the pore diameter is small, A large number of holes having a uniform shape and size can be formed. Further, since the decomposition start temperature of the fine particles is low and constant, almost all the pore forming materials are decomposed earlier and more quickly than the binder resin. For this reason, in the various processes for forming a porous metal sintered body of degreasing and sintering, the molded body and the sintered body are not damaged, and the residual carbon is not left in the sintered body, and the porosity is high. A sintered body can be manufactured stably and easily.
In particular, when the manufacturing method is used for manufacturing an anode element of an electrolytic capacitor, pores can be stably formed in the anode element, and the cathode forming electrolyte solution can be easily infiltrated. As a result, even when a valve metal powder having a small particle size is used, holes can be formed, and the large capacitance inherent in the valve metal powder having a small particle size can be realized. Performance can be improved.

(First embodiment)
A first embodiment in the method for producing a porous metal sintered body of the present invention will be described. The manufacturing method of the first embodiment is a so-called dry method. First, a mixture containing metal powder, a hole forming material, and a binder resin is filled in a mold and a molded body is formed by press molding or the like. Thereafter, the molded body is heated to a temperature higher than the decomposition temperature of the pore-forming material to thermally decompose the pore-forming material, and then the molded body is sintered at a sintering temperature higher than this to sinter porous metal. Form the body.

The metal material constituting the metal powder is not particularly limited. For example, Fe, Ni, Co, Cr, Mn, Zn, Pt, Au, Ag, Cu, Pd, Al, W, Ti, V, Mo, Nb, Zr , Ta, etc., or an alloy containing at least one of these. The metal powder preferably has a purity of 99.5% or more, and is preferably an aggregated powder having a volume average particle diameter of 1 to 100 μm in order to form a stable porous body. Among metal powders, in terms of suitability as a capacitor element, those made of valve metal and having a CV value of 100 kCV or more are preferable. Examples of the valve action metal include tantalum, aluminum, niobium, and titanium. Among these valve action metals, tantalum and niobium are preferable, and tantalum is particularly preferable.
Further, the primary particle diameter is preferably 0.01 to 5.0 μm, more preferably 0.01 to 1.0 μm, because it can have a high capacity when used as a capacitor element.
The metal powder may be an agglomerated powder in which primary particles are agglomerated. Moreover, the metal granulated powder granulated using resin may be sufficient. In the case of metal granulated powder, a molded body can be formed by mixing with a pore forming material as it is and performing press molding.

The pore-forming material in the present invention is polyhydroxyalkanoate particles produced in the cells of a microorganism. Although the polyhydroxyalkanoate of the present invention has been chemically synthesized, it is difficult to carry out high molecular weight polymerization with stereoregularity, which is behind the method using microorganisms that have already begun industrial production studies. ing. Moreover, even if synthesized by a chemical method, it is expected that there will be difficulties in terms of further uniform particle formation.
The polyhydroxyalkanoate of the present invention is a condensation polymer of 3-hydroxyalkanoate represented by the following formula (1), wherein R is an alkyl group represented by C _n H _{2n + 1} , and n = 1 to 15 It is preferable that

Specific examples of 3-hydroxyalkanoates include: n = 1 3-hydroxybutyrate, n = 2 3-hydroxyvalerate, n = 3 3-hydroxyhexanoate, n = 4 3-hydroxyhepta Noate, 3-hydroxyoctanoate with n = 5, 3-hydroxynonanoate with n = 6, 3-hydroxydecanoate with n = 7, 3-hydroxyundecanoate with n = 8, n = 9 3-hydroxydodecanoate etc. are mentioned, These homopolymers may be sufficient and a copolymer may be sufficient.
Among polyhydroxyalkanoates, a copolymer (PHBH) of 3-hydroxybutyrate with n = 1 and 3-hydroxyhexanoate with n = 3 is preferable.

Examples of microorganisms that produce polyhydroxyalkanoates include A. lipolytica, A.I. eutrophus, A.M. Examples include alkalis such as latus, Alcaligenes, Pseudomonas, Bacillus, Azotobacter, Nocardia, Aeromonas and the like. Among these, A. A strain such as Caviae, and Alcaligenes eutrophus AC32 (FERM P-15786) (J. Bacteriol., 179, pages 4821-4830 (1997)) into which genes of the PHA synthase group have been introduced are preferred.
By culturing these microorganisms under appropriate conditions, it is possible to obtain microbial cells in which polyhydroxyalkanoate is accumulated in the microbial cells. Separation can be performed to remove the polyhydroxyalkanoate.

In production using microorganisms, usually only one of the optical isomers is selectively produced, so that the uniformity of chemical and physical properties is high and the chemical structure is homogeneous. For this reason, the distribution of the decomposition temperature is narrow, and the entire amount is rapidly decomposed within a certain temperature range. Furthermore, it has high hardness and is less likely to be deformed in the process of forming a molded body.
Furthermore, the polyhydroxyalkanoate produced using these microorganisms is chemically stable to many organic solvents, and dissolves when mixed with metal powder, binder and organic solvent to form a slurry. Since it hardly swells and the solvent for producing the porous sintered body by the wet method is hardly limited, it can be suitably used particularly in the wet method.
Polyhydroxyalkanoates produced using these microorganisms are characterized by their small particle size and uniform particle size distribution because they are regulated by the shape and size of the individual microorganisms. For this reason, the shape and size can be adjusted by selecting the genus species of the microorganism. It can also be controlled by the culture conditions when the microorganism produces polyhydroxyalkanoate.
Thus, the diameter of the pores formed in the porous metal sintered body can be controlled by the particle diameter of the polyhydroxyalkanoate. Further, the number of holes can be controlled by the added amount. For this reason, by selecting the particle size and addition amount of polyhydroxyalkanoate, it has good mechanical strength according to the type of metal powder used and the size of its primary particle size, and for each application It is possible to realize the size, number, and distribution of adapted holes. When a porous metal sintered body is used for an electrolytic capacitor, it is possible to form a more appropriate hole, and more easily permeate the electrolyte solution for forming a cathode while suppressing a decrease in capacity and increasing the capacity. The particle diameter of the hydroxyalkanoate is particularly preferably 1 to 10 μm. The amount added is preferably 1 to 50% in volume ratio with the metal powder in order to form effective pores without reducing the mechanical strength of the sintered metal, and 5 to 30%. More preferably.
In addition, in order to take out the polyhydroxyalkanoate produced in the cells of the microorganism as fine particles, the polyhydroxyalkanoate containing the polyhydroxyalkanoate is treated with a proteolytic enzyme, a surfactant, or functional water to obtain polyhydroxyalkanoate. A method of solubilizing cellular materials other than those and taking out polyhydroxyalkanoate fine particles is used (Japanese Patent Laid-Open Nos. 60-145097 and 2000-166585).

A known binder resin can be used as the binder resin. Suitable binder resins include, for example, polyvinyl alcohol, polyvinyl acetal, butyral resin, phenol resin, acrylic resin, urea resin, polyurethane, polyvinyl acetate, epoxy resin, melamine resin, alkyd resin, nitrocellulose resin, and natural resin. Can be mentioned. These resins can be used alone or in admixture of two or more.
Among these, an acrylic resin is preferable. Since the acrylic resin decomposes almost completely after the binder is decomposed and removed in a vacuum and does not remain as carbon, the electrolytic capacitor using the acrylic resin can keep the leakage current low.
The glass transition point of the binder resin is preferably 50 ° C. or less, and more preferably room temperature or less. If the glass transition point of the binder resin is 50 ° C. or lower, the molded body can be made flexible, so that damage during the process up to the completion of sintering can be reduced.
The content of the binder resin in the raw material mixture is preferably in the range of 0.01 to 30 parts by mass, particularly preferably in the range of 0.01 to 15 parts by mass per 100 parts by mass of the metal powder.
As a method for forming a molded body containing a metal powder, a binder resin, and a pore-forming material by a dry method that does not go through a coating step, a known method can be widely used. For example, it is possible to use a method in which metal powder granulated using a resin and a pore-forming material are mixed by stirring to form a mixture, and the mixture is filled in a mold and press-molded.
Also, the metal powder and binder resin are dissolved in a solvent and sprayed onto the surface of the metal powder, the metal powder coated with the binder resin and the pore-forming material are mixed by stirring, and press-molded with a mold to form a molded body. You can also.

  In order to manufacture a porous metal sintered body for an electrolytic capacitor anode element by a dry method, a hole forming material made of valve action metal powder, binder resin and polyhydroxyalkanoate is mixed and filled in a mold. Next, a tantalum wire to be a lead wire is planted and dried, for example, at about 60 ° C. for about 60 to 120 minutes, and then heat treated at about 300 to 600 ° C. in a vacuum to form a pore forming material and a binder resin in the molded body Remove. Furthermore, high-temperature heat treatment (sintering) is performed at about 1200 to 1600 ° C. for about 10 to 30 minutes, and the metal powders and the metal powder and the lead are fused. Thereby, the porous metal sintered body integrated with the lead wire for forming the electrolytic capacitor anode element can be obtained.

(Second Embodiment)
A second embodiment of the method for producing a porous metal sintered body of the present invention will be described.
The manufacturing method of the second embodiment is a wet method. First, a metal powder, a pore forming material, a binder resin, and a solvent are mixed and dispersed, and a paint-like metal powder dispersion is preferably prepared. The metal powder dispersion is applied or printed on a substrate to produce a coated or printed material, and then the substrate is peeled off from the coated or printed material to form a molded body. The step of forming the porous metal sintered body from the molded body is the same as in the first embodiment. In addition, in the manufacturing method of the second embodiment, the metal powder, the hole forming material, and the binder resin can be used those soluble in the solvent from the first embodiment. Is omitted.

Examples of the solvent constituting the metal powder dispersion include water, alcohols such as methanol, IPA (isopropyl alcohol) and diethylene glycol, cellosolves such as methyl cellosolve, ketones such as acetone, methyl ethyl ketone and isophorone, and N, N-dimethyl. Examples include amides such as formamide, esters such as ethyl acetate, ethers such as dioxane, chlorinated solvents such as methyl chloride, and aromatic hydrocarbons such as toluene and xylene. These may be used alone or in combination. Can be used. Among these, those that do not dissolve the polyhydroxyalkanoate are preferable because the pore diameter can be more easily controlled. Solvents that do not dissolve the polyhydroxyalkanoate include, for example, water, alcohols such as methanol, IPA (isopropyl alcohol) and diethylene glycol, cellosolves such as methyl cellosolve, ketones such as acetone, methyl ethyl ketone, and isophorone, N, N -Amides such as dimethylformamide, esters such as ethyl acetate, ethers such as dioxane, aromatic hydrocarbons such as toluene and xylene, and the like can be used alone or in admixture of two or more.
The content of the solvent in the metal powder dispersion is set to such an extent that the step of applying or printing the metal powder dispersion on an appropriate substrate surface can be performed smoothly.

  In addition to the metal powder, binder resin, and solvent, the metal powder dispersion has suitable physical properties for applying or printing the metal powder dispersion on an appropriate substrate surface, and keeps the dispersion of the metal powder stable. Therefore, various additives can be appropriately blended. Suitable additives include, for example, dispersants such as phthalate esters, phosphate esters and fatty acid esters, plasticizers such as glycols, low-boiling alcohols, antifoaming agents such as silicone-based or non-silicone-based agents, silane coupling agents, Examples include titanium coupling agents and dispersants such as quaternary ammonium salts.

The compounding ratio of each component in the metal powder dispersion is, for example, 0.01 to 30 parts by mass, preferably 0.01 to 15 parts by mass, and 5 to 160 parts by solvent for 100 parts by mass of the metal powder. The part by mass and the additive are 5 parts by mass or less.
The viscosity of the metal powder dispersion is about 0.1 to 1000 Pa · sec, preferably about 0.1 to 100 Pa · sec, from the viewpoint of applicability and handleability.

In the preparation of the metal powder dispersion, the metal powder, the pore forming material, the binder resin, the solvent and the additive may all be dispersed at the same time using various kneading / dispersing machines, or sequentially mixed and dispersed. May be.
As kneading and dispersing machines, roll type kneaders such as two rolls and three rolls, vertical kneaders, pressure kneaders, blade type kneaders such as planetary mixers, ball type rotary mills, sand mills, attritors, etc. Examples include a disperser, an ultrasonic disperser, and a nanomizer.

Next, the metal powder dispersion is applied or printed on the substrate and then dried to volatilize the solvent in the metal powder dispersion, and the metal powder and binder resin (the solvent may remain) on the substrate. A thin sheet (molded body) is formed.
Here, as the substrate, a metal powder dispersion, particularly a glass or a synthetic resin sheet that is stable to a solvent can be used, and preferably a polyethylene terephthalate film (PET film) provided with a release layer made of polyvinyl alcohol resin or the like. Etc. are used.

The release layer can be formed by applying a release layer coating on the substrate. By forming the release layer on the substrate, the coating film formed from the metal powder dispersion located on the release layer can be easily peeled off from the substrate as it is, and the release layer remaining on the coating film is then metallized. It can be made to function also as a protective layer which prevents destruction of the coating film which consists of a dispersion liquid.
The resin used for the release layer is a binder in the metal powder dispersion in order to improve the adhesion between the release layer and the layer made of the metal powder dispersion, and to facilitate the release from the interface between the release layer and the substrate. What is compatible with the resin is preferably used. Examples of the release layer resin include polyvinyl alcohol, polyvinyl acetal, butyral resin, and acrylic resin.
The thickness of the release layer is preferably in the range of 1 to 20 μm, and in particular in the range of 1 to 10 μm, the residual carbon after sintering of the release layer remaining on the coating film can be reduced, and the release layer It is more preferable because the strength of the coating film can be kept moderate.

  Examples of the method for applying the metal powder dispersion include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, and cast coating. , Spray coat and the like.

  Examples of the printing method of the metal powder dispersion include a stencil printing method, an intaglio printing method, and a lithographic printing method. Among these, the stencil printing method is preferable because the shape of the sintered compact can be formed into a desired shape such as a rectangular parallelepiped shape, a cylindrical shape, or a comb tooth shape.

The thickness of the sheet (molded product) obtained by coating or printing can be set as appropriate, and the thickness (wet thickness) of the coated product (printed product) before drying is, for example, in the range of several μm to 300 μm. obtain. In addition, the obtained sheet (molded body) can be cut into a desired shape by slitting, punching, or the like before or after peeling from the substrate, if necessary.
Such a wet method is easy to make the porous metal sintered body thinner than the dry method.

  In the porous metal sintered body manufacturing method according to the first and second embodiments described above, polyhydroxyalkanoate particles produced in the cells of microorganisms are used as the pore forming material. Since the polyhydroxyalkanoate produced in the cells of the microorganism has a uniform chemical structure, the difference between the decomposition start temperature and the decomposition end temperature is small (that is, rapidly decomposes) in the thermal decomposition curve (see FIG. 1). ) And the decomposition end temperature is lower than that of the binder resin. For this reason, in the heat treatment step, the binder resin disappears after the pore forming material disappears and the pores are formed. Since the pore forming material and the binder resin disappear in this order, the structure can be sintered in a defined state, so that the desired pores can be easily formed in the porous metal sintered body, and the porous metal sintered The body pore size distribution can be easily controlled. For example, pores larger in diameter than pores formed in the gaps between the primary particles of the metal powder can be formed in the porous metal sintered body.

The porous metal sintered body obtained by the manufacturing method of the first and second embodiments is used as an electrolytic capacitor anode element for manufacturing an electrolytic capacitor. Hereinafter, the manufacturing method of the anode element for electrolytic capacitors using the said porous metal sintered compact is demonstrated.
In order to manufacture an electrolytic capacitor anode element by a dry method, a mold is filled with a mixture of granulated powder prepared by mixing liquid binder resin and valve action metal powder, and a pore forming material. When forming a sintered compact, a lead wire made of a valve metal is placed in the mold and then filled with the mixture, or the lead wire is planted in the mixture after filling the mixture. Then, the lead wire is fixed to the molded body, and the molded body is sintered to fuse the lead wire and the valve metal.
Further, in the wet method, as shown in FIG. 2, a lead 12 is placed on a sheet-like molded body 11a obtained by the wet method, and another sheet-shaped molded body 11b is overlaid, and if necessary, an appropriate one is obtained. By applying a pressure treatment, the two sheet-like molded bodies 11a and 11b and the lead 12 are brought into close contact with each other to form the joined body 13. Alternatively, the joined body 13 may be formed by bending a single wide sheet in half and sandwiching the leads 12 therebetween and laminating them.
Next, the joined body 13 is dried at about 60 ° C. for about 60 to 120 minutes, for example, and then heat treated at about 300 to 600 ° C. in vacuum to remove the pore forming material and the binder resin in the molded bodies 11a and 11b. To do. Furthermore, high-temperature heat treatment (sintering) is performed at about 1200 to 1600 ° C. for about 10 to 30 minutes to fuse the valve action metal powders and the valve action metal powders and the leads. Thereby, the lead | read | reed 12 is provided between the molded objects 11a and 11b, and the anode element for electrolytic capacitors with which these were integrated can be obtained.

In order to obtain an electrolytic capacitor using the above anode element for an electrolytic capacitor, first, a porous metal sintered body is placed in an electrolytic solution tank, and then subjected to chemical conversion treatment by applying a predetermined DC voltage, so that the porous metal An oxide film is formed on the surface of the sintered body. Next, a cathode forming electrolyte solution that is a manganese dioxide solution or a functional polymer solution is infiltrated to form a manganese dioxide coating or a functional polymer coating solid electrolyte on the oxide coating. Subsequently, a carbon (graphite) layer and a silver paste layer are formed on the capacitor anode element on which the oxide film / manganese dioxide film or functional polymer film is formed, and the cathode treatment is performed. Then, as shown in FIG. 3, one end side of the cathode terminal 22 is joined to the surface of the capacitor anode element 21 with a conductive adhesive 24, and the tip portion 25 of the lead 23 is joined to the anode terminal 26 by spot welding. Thereafter, the electrolytic capacitor 20 can be obtained by applying the resin sheathing 27, for example, by resin molding or by immersing it in a resin solution.
By using the sintered body for an electrolytic capacitor anode element using the porous metal sintered body produced by the above-described production method as in the production of the above electrolytic capacitor, a high capacitance can be realized. Even when a valve metal powder having a small particle diameter is used, a sintered body having a high porosity can be formed, so that the electrolyte solution for forming a cathode can be easily penetrated.

  Note that the present invention is not limited to the above-described embodiments. In the embodiment described above, the lead is provided on the molded body, but the lead may not be provided. A porous metal sintered body having no lead can be used as a molding material for metal parts.

An example is given and explained below about the manufacturing method of the porous metal sintered compact of the present invention.
Example 1
50 g of tantalum metal powder S-15 (manufactured by Cabot Super Metal Co., Ltd.) having an average primary particle size of 0.1 μm and an electrostatic capacity of 150 kCV / g, and PHBH resin beads having an average primary particle size of 1 μm as pore forming materials ( Kaneka Chemical Co., Ltd.) 0.5 g (1% by mass relative to tantalum metal powder), acrylic resin “NCB-166” (Dainippon Ink & Chemicals, glass transition point: −10 ° C.) as binder resin 7.5 g (solid content: 3 g), 4.8 g of cyclohexanone (solvent), and 300 g of zirconia having a diameter of 3 mm are placed in a plastic bottle, and mixed and dispersed using a shaker (paint conditioner). Obtained.
On the other hand, a solution of acrylic resin “IB-30” (manufactured by Fujikura Kasei Co., Ltd.) was developed with a # 16 wire bar on a PET film having a thickness of 50 μm to provide a release layer having a thickness of 4 μm.
Next, the above-mentioned metal powder dispersion is spread on a PET film provided with a release layer with an applicator having a predetermined depth and dried at about 60 ° C. for about 60 to 120 minutes to disperse a metal powder having a thickness of 200 μm. A liquid dry coating was obtained.
A sheet (molded body) of a dried coating film is peeled off from the substrate, and another sheet of a dried coating film is superposed on the sheet, and a pressure treatment is performed to bring the two sheets into close contact with each other. A molded body having a size of 20 mm was formed. In order to obtain a measurement sample for accurately measuring the pore distribution of the sintered body, no lead wire was sandwiched between the sheets.

Next, the molded body thus obtained was subjected to a heat treatment step in vacuum at about 400 ° C. for 4 hours to remove organic substances (binder resin and PHBH resin beads), and further about 20 minutes at about 1200 ° C. High temperature heat treatment (sintering) was performed. The degree of vacuum reached at this time was 2.67 × 10 ⁻⁷ Pa. Thus, a sheet-like tantalum porous sintered body was obtained by fusing tantalum metal powders together.

0.292 g of the obtained tantalum porous sintered body was put into a sample cell of a porosimeter (Pore Sizer 9320, manufactured by Shimadzu Corporation), and the pore distribution was measured by a mercury intrusion method. The cell constant at this time was calculated as 10.79 μl / pF, the contact angle was 130 degrees, the surface tension was 484 dynes / cm, and the mercury specific gravity was 13.6462.
The total pore volume at this time was 0.179 ml / g, the mode diameter was 0.41 μm, the apparent density was 3.19, and the porosity was 57.0%. The pore distribution diagram is shown in FIG.

(Example 2)
A paint was prepared in the same manner as in Example 1 except that the blending amount of PHBH resin beads having an average primary particle diameter of 1 μm (manufactured by Kaneka Chemical Co., Ltd.) was 1.0 g (2 mass percent with respect to tantalum metal powder) A molded body was produced, and a sintered sheet-like tantalum porous sintered body was obtained. 0.495 g of the obtained tantalum porous sintered body was put into a sample cell of a porosimeter, and the pore distribution was measured by a mercury intrusion method.
At this time, the total pore volume was 0.166 ml / g, the mode diameter was 0.37 μm, the apparent density was 3.41, and the porosity was 56.6%. The pore distribution diagram is shown in FIG.

(Comparative Example 1)
Except not including PHBH resin beads (manufactured by Kaneka Chemical Co., Ltd.) having an average primary particle size of 1 μm, it is made into a paint in the same manner as in Example 1 to produce a molded body. A sintered body was obtained. 0.265 g of the obtained tantalum porous sintered body was put in a sample cell of a porosimeter, and the pore distribution was measured by a mercury intrusion method.
At this time, the total pore volume was 0.165 ml / g, the mode diameter was 0.24 μm, the apparent density was 3.32, and the porosity was 54.9%. A pore distribution diagram is shown in FIG.

As apparent from FIGS. 4 to 6, in Example 1 and Example 2, in addition to holes having a peak in the same hole diameter as in Comparative Example 1, a sharp peak is formed at a position where the hole diameter is larger than the hole. It can be seen that another hole is formed. In FIG. 7, the pore distributions of the porous tantalum sintered bodies produced in Example 1, Example 2 and Comparative Example 1 were overlapped with the horizontal axis in common so that the change in the pore distribution became clearer. . That is, the hole distribution is shifted in the direction of increasing the hole volume, and the mode diameter is increased. Since the specific gravity of tantalum is large and the amount of PHBH added is not large, there is no difference in apparent density or total pore volume, but the effect of adding PHBH is clear. Therefore, the pore distribution in the porous metal sintered body can be controlled by adjusting the particle size and addition amount of the polyhydroxyalkanoate particles. The reason why the peak position is smaller than 1 μm may be that the pores are slightly crushed by the weight of tantalum due to fusion during sintering.
Thus, when the method for producing a porous sintered body of the present invention is applied to the production of a porous sintered body for a tantalum electrolytic capacitor, even if a tantalum powder having a CV value of 10 kCV or more is used, Since sufficient pores can be formed, the electrolyte solution can be deeply penetrated into the sintered body. Therefore, it is possible to manufacture a small electrolytic capacitor having a high capacitance.

It is an example of the thermal decomposition curve of the polyhydroxyalkanoate and binder resin which were produced in the cell of microorganisms. It is a perspective view explaining the manufacturing method of the porous metal sintered compact of this invention. It is a schematic block diagram which shows an example of an electrolytic capacitor. 2 is a graph showing the pore size distribution of a porous metal sintered body in Example 1. FIG. 4 is a graph showing the pore size distribution of a porous metal sintered body in Example 2. 5 is a graph showing the pore size distribution of a porous metal sintered body in Comparative Example 1. It is the graph which piled up the graph which shows the hole diameter distribution of the porous metal sintered compact in Example 1, Example 2, and the comparative example 1 by making a horizontal axis into common.

Claims (7)

  After forming a molded body containing a metal powder, a pore-forming material and a binder resin, heating the molded body to a temperature higher than the decomposition temperature of the pore-forming material to thermally decompose the pore-forming material, In the method for producing a porous metal sintered body in which the compact is sintered at a sintering temperature higher than the heating temperature, the pore-forming material is a polyhydroxyalkanoate particle produced in the cells of a microorganism. A method for producing a porous metal sintered body characterized by the above.   The molded body is formed by applying or printing a metal powder dispersion containing a metal powder, a pore forming material, a binder resin, and a solvent on a substrate to form a coated product or a printed material, and then forming the coated product or the printed material from the coated material or the printed material. The method for producing a porous metal sintered body according to claim 1, wherein the porous metal sintered body is formed by peeling off the metal. The polyhydroxyalkanoate has the following formula (1)

3. In the formula, R is a condensation polymer of a compound represented by C _n H _{2n + 1} (n is an alkyl group or a hydrogen atom represented by 1 to 15). The manufacturing method of the porous metal sintered compact of description.   The polyhydroxyalkanoate is a copolymer of n = 1 3-hydroxybutyrate and n = 3 3-hydroxyhexanoate in the compound represented by the formula (1). Of manufacturing a porous metal sintered body.   The method for producing a porous metal sintered body according to claim 1 or 2, wherein the metal powder is made of a valve metal and has a CV value of 100 kCV or more.   The method for producing a porous metal sintered body according to claim 5, wherein the valve metal is tantalum.   The method for producing a porous metal sintered body according to claim 5, wherein the molding is sintered after providing a lead.

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