JPH06240304A - Fine metal powder aggregate, porous metal sintered compact and production thereof - Google Patents

Abstract

PURPOSE:To obtain a lightweight sintered compact enhanced in porosity by specifying the diameter of a hollow metal fine grain and the relation between the thickness of a metal layer and the diameter of the-hollow part and shaping the fine grain. CONSTITUTION:The shell 2 of-the fine metal powder aggregate is formed with a metal layer, and the inside 3 is formed with a hollow metal fine grain 1. When the diameter A of the fine grain 1 is controlled to 1-20mum, 0.05mum<=D and D/R<=0.25, where D is the thickness of the metal layer 2 and R is the diameter of the hollow part 3. When the diameter A is controlled to 20mum to 2mm, 0.05mum<=D<=5mum. An opening 4 is formed at a part of the metal layer 2. The aggregate is heated between the temp. about 25% lower than the m.p. of the metal constituting the aggregate and the temp. lower than the m.p. and sintered, and the porous metal sintered compact is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hollow metal fine particle aggregate shaped body obtained by shaping novel metal fine particles (hollow metal fine particles) having a hollow inside into a desired shape, and at least a part of the hollow metal fine particles or a crushed product thereof. And a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, since a sintered body of fine metal powder is porous and has a large surface area, an oil-impregnated bearing material; a mold,
Rolling tools, cutting tools, machine parts, electrical contacts, friction materials,
Filters, magnetic parts, aircraft parts, automobile parts, wear-resistant parts; conductor materials, resistance materials, contact materials, electrode materials, sealing materials, pyroelectric materials; microtube materials, dielectric materials, capacitor materials, piezoelectric materials, surface acoustic waves Materials, high magnetic permeability materials, microwave materials, magnet materials, magnetostrictive materials; semiconductor materials, thermoelectric materials, photoelectric materials, electron emission materials; electromagnetic wave shielding materials, battery electrode materials, catalyst materials for chemical reactions, sensor materials; It is used as a gas adsorbent, sound insulation material, temperature insulation material, etc.

When such a porous metal sintered body is used for various purposes, it is preferable to maximize the surface area. Since the surface area of the porous metal sintered body is increased as the particle size of the fine metal powder used is smaller, research is being conducted in the direction of minimizing the particle size of the fine metal powder as a sintering raw material.

For example, the groups of Birringer and Gleiter (West Germany) and Siegel and Hahn (USA) et al. Produced ultrafine metal particles in order to obtain a dense sintered body of ultrafine metal particles without contacting them with the atmosphere and then directly producing them. The method of sintering is adopted. Specifically, the ultrafine particles generated by the evaporation method in a gas are directly reduced in pressure in a high vacuum to a pressure of several GPa and sintered at low temperature to obtain a sintered body having an ultrafine structure with a nanometer-order particle size. Manufacturing ((1) R.
W. Siegel and H. Hahn: Nanophase Materais. In CUR
RENT TRENDS IN THE PHYSICS OF MATERALS. M. Yussouf
f ed., world Scientific Publ. Co ,. Singapore. p. 40
3 (1987)).

In addition to the above, Hayashi et al. Obtained a sintered body having a large surface area by a method of reducing and sintering the ultrafine metal powder that has been gradually oxidized. That is, the finely divided metal ultrafine particles are skillfully combined with forming, reducing and sintering operations to obtain a sintered body having a fine structure. For example, in the case of Cu ultrafine powder, micron-sized and submicron-sized sintered bodies are obtained by pressureless or pressure sintering ((2) Hiroji Hayashi, Hiroshi Kihara: Fe and Cu metal alloys Densification and grain growth by differential sintering.The Japan Institute of Metals, vol. 50,
No. 12. pp.1089-1094 (1986). (3) Hiroji Hayashi, Hiroshi Kihara: F
e Densification and grain growth in pressure sintering of ultrafine powder, see Japan Institute of Metals, vol. 52, No. 3 pp.343-347 (1988)).

By adopting these methods, it is possible to obtain a metal sintered body having an extremely large surface area. However, when adopting these methods, special equipment is required. Is extremely valuable, but it is not suitable as a method for industrially mass-producing a metal sintered body. That is, there is a problem that the cost of the metal sintered body manufactured by these methods becomes very high.

[0007]

It is an object of the present invention to contain a porous metal sintered body which has a high porosity and is lightweight, and hollow metal fine particles suitable for producing such a sintered body, which are given a predetermined shape. It is an object of the present invention to provide a shaped shaped body and a method for easily manufacturing the above-mentioned sintered body and shaped body.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the inside is hollow metal fine particles, and the particle diameter of the hollow metal fine particles is in the range of 1 μm to 2 mm, and the thickness D of the metal layer forming the hollow metal fine particles is The diameter R of the hollow portion of the hollow metal fine particles has a relationship of 0.05 μm ≦ D and D / R ≦ 0.25 when the diameter of the hollow metal fine particles is 1 to 20 μm. If the particle size of the particles exceeds 20 μm and 2 mm or less, 0.05 μm ≦ D
A metal fine powder aggregate powder having a relationship of ≦ 5 μm and a hollow metal fine particle-containing metal particle group containing hollow metal fine particles having openings in at least a part of the metal layer is shaped into a predetermined shape. In the form.

In the present invention, the inside is hollow metal fine particles, and the particle diameter of the hollow metal fine particles is in the range of 1 μm to 2 mm, and the thickness D of the metal layer forming the hollow metal fine particles and the hollow The diameter R of the hollow portion of the metal fine particles has a relationship of 0.05 μm ≦ D and D / R ≦ 0.25 when the particle diameter of the hollow metal fine particles is 1 to 20 μm. If the diameter exceeds 20 μm and 2 mm or less, 0.05 μm ≦ D
A porous metal sintered body having a relationship of ≦ 5 μm, and at least a part of hollow metal fine particles having openings in at least a part of the metal layer or a crushed product thereof is fused. It is in.

The metal fine powder aggregate shaped product of the present invention is obtained by shaping a large number of metal-coated polymer particles having a metal layer on the surface of a core material particle made of an organic polymer into a predetermined shape and then obtaining the obtained metal-coated polymer. It can be produced by removing the core material made of an organic polymer from the particle shaped body.

The porous metal sintered body of the present invention is obtained by shaping a large number of metal-coated polymer particles having a metal layer on the surface of core particles made of an organic polymer into a predetermined shape. A core material made of an organic polymer is removed from the coated polymer particle shaped body to form a metal fine powder aggregated shape forming body, and the metal fine powder aggregated shape forming body is formed at a temperature of 25 or more than the melting point of the metal forming the shape forming body. % To a temperature below the melting point and then sintered to sinter.

Since the sintered body of the present invention is a porous body composed mainly of hollow metal fine particles, it has a very high porosity and is lightweight. The porous sintered body can be easily manufactured by producing a shaped body having a large number of hollow metal fine particles in a predetermined shape and sintering the shaped body.

Since the sintered body having such characteristics has a large surface area and can increase the activity of metal, it is extremely useful as a raw material for a functional metal material.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below.
FIG. 1 schematically shows an example of the cross-sectional structure of the hollow metal fine particles constituting the metal fine particle aggregate-shaped body and the porous metal sintered body of the present invention.

As shown in FIG. 1, the metal fine particle aggregate-shaped body and the porous metal sintered body of the present invention have a hollow 2 formed of a metal layer, and a hollow metal fine particle 1 formed in an interior 3. The diameter A of the hollow metal fine particles is in the range of 1 μm to 2 mm, preferably 1 μm to 1 mm, particularly preferably 1 to 1
Within the range of 00 μm. As the particle size decreases, the proportion of metal in the hollow metal fine particles increases, and the metal layer can be used more efficiently.

The hollow metal fine particles 1 have a particle size A of 1 to
When the thickness of the metal layer forming the outer shell 2 of the hollow metal fine particles is D and the diameter of the hollow portion 3 of the hollow metal fine particles is R in the range of 20 μm, the thickness D of the metal layer 2 is , 0.05 μm ≦ D, and D / R ≦ 0.25. That is, the diameter A of the hollow metal particles is 1 to
Within the range of 20 μm, the minimum thickness of the metal layer 2 is 0.1.
05 μm, and the hollow portion 3 of the hollow metal fine particles
The total (2D) of the thickness D of the metal layer 2 does not exceed 1/2 of the diameter R of the hollow portion 3 with respect to the diameter R.

The particle diameter A of the hollow metal fine particles is 20.
If the thickness exceeds μm and is 2 mm or less, the thickness D of the metal layer 2
Has a relationship of 0.05 ≦ D ≦ 5 μm. Even in this case, the thickness D of the metal layer with respect to the diameter R of the hollow portion 3 naturally has a relationship of D / R ≦ 0.25, and the diameter R of the hollow portion 3 of the hollow metal fine particles is On the other hand, the total thickness D of the metal layer 2 (2D) is 1 / the diameter R of the hollow portion 3.
It does not exceed 2.

Further, an opening 4 is formed in at least a part of the metal layer 2 of the hollow metal fine particles. This opening is, for example, a scanning electron microscope (SEM) shown in FIG.
It may be formed like a defective portion of the metal layer as shown in the photograph, or, as shown in FIG. 4, in order to form the hollow portion 3 of the hollow metal fine particles, the core material is gasified by, for example, thermal decomposition. It may be formed like a through hole formed in the metal layer 2 in order to be evaporated and removed from the metal-coated polymer particles. Further, as shown in the upper part of FIG. 5, in a crack-like form caused by volatilization of the polymer forming the core material in a part of the continuous body of metal particles in which the metal grain boundaries of the metal layer have disappeared. As shown in the lower photograph of FIG. 5, the metal grain boundaries of the metal layer disappear to form a mesh-shaped metal layer, and the openings are formed in the metal layer itself in a non-uniform mesh shape. It may have a different form. Also,
As shown in FIGS. 6 and 7, when the metal layer is relatively thick, an opening formed so that the metal layer is broken by volatilization of the organic polymer that is the core material when the core material is removed. It may be a portion or an opening formed in a crack shape.

The opening area of the openings having various forms as described above is usually 1/2 or less of the surface area of the outer shell formed by the metal layer. For example, in the case of an opening having the form shown in FIGS. 3 and 4, the opening area is
It is often 10% or less of the surface area of the shell formed by the metal layer. For example, as shown in FIG. 5, the diameter of the opening B having a through-hole shape is 0.05 of the diameter A of the hollow metal fine particles.
It is often about 10%. When the particle diameter of the hollow metal fine particles is relatively large and the thickness of the metal layer is relatively thick, a part of the metal layer in which the metal grain boundaries of the hollow body disappears as shown symbolically in FIG. Often a cracked opening is formed.

The metal forming the metal layer 2 which is the outer shell of the hollow metal fine particles 1 having the above structure is not particularly limited, and various metals or at least some of these metals are metal-containing compounds such as oxides. It may be. Examples of metals forming this metal layer include copper, iron, nickel, cobalt, cadmium, lead, zinc, arsenic, tin, titanium, silver,
Mention may be made of gold, palladium, platinum, rhodium and ruthenium. Further, this metal layer may be formed of an alloy based on these metals. Examples of such alloys are nickel alloys such as nickel-cobalt, nickel-cobalt-boron, nickel-cobalt-phosphorus, nickel-iron-phosphorus, nickel-tungsten-phosphorus and nickel-phosphorus; cobalt-iron- Phosphorus, cobalt-
Tungsten-phosphorus and cobalt-nickel-manganese-
Examples thereof include cobalt alloys such as rhenium-phosphorus; iron alloys and the like. Further, in the metal layer, the above metal or alloy may have a uniform composition,
It may have a non-uniform composition.

The metal fine powder aggregate shaped body of the present invention is a shaped body (preform, sintering precursor) in which the above-mentioned numerous hollow metal fine particles are shaped into a predetermined shape. If the hollow metal fine particles are pressed and shaped as they are, the hollow portion is crushed and a shaped product of hollow metal fine powder cannot be manufactured. Therefore, in the present invention, this is shaped into a predetermined shape using the metal-coated polymer particles before removing the core material,
Then, the core material is removed from the shaped body of the metal-coated polymer particles thus shaped to produce the metal powder aggregate shaped body of the present invention.

The method for producing the metal powder aggregate shaped body will be described below. The metal-coated polymer particles are produced by forming a metal layer on the surface of core material particles made of an organic polymer.

The organic polymer used here includes an amorphous polymer, a needle-shaped polymer, a spherical polymer, a protrusion-shaped polymer, and an octopus-shaped polymer. Depending on the intended use of the resulting hollow metal particles. Although various shapes can be used, it is preferable to use a spherical organic polymer in the present invention.
By using the spherical core material, the thickness of the metal layer formed on the core material can be made relatively uniform.

The core material is usually 0.5 μm.
Spherical particles having a particle diameter of m or more can be used, and a metal can be deposited on the surface of a spherical core material of such a size, but when the particle diameter of the core material is 1 μm or less, a continuous metal is formed. Since it is difficult to form a layer, a core material having a particle size of 1 μm or more is usually used in the present invention. In addition, since the core material with particles larger than 2 mm has a small curvature,
For example, according to the electroless plating method, the metal layer can be easily formed in an extremely short time, but the reaction for forming the metal layer proceeds remarkably fast, and the thickness of the metal layer effectively removes the core material. It is difficult to control the thickness to the extent possible.

Such a core material is formed of an organic polymer. The organic polymer used here is an organic polymer that can be removed so that the metal layer can maintain its form by elution and removal with a solvent, thermal decomposition by heating, and application of thermal energy such as radiation and electromagnetic waves. Examples of such organic polymers include crosslinked polymers and non-crosslinked polymers, and include (meth) acrylic resins, styrene resins, styrene / (meth) acrylic resins, polyethylene resins, polypropylene resins. Resin, ABS resin, AS
Resin, polyacetal resin, polycarbonate resin,
Examples include phenolic resins, epoxy resins, polyester resins, polyamide resins, urethane resins and polyimide resins. Among these organic polymers, when the core material is removed by heating, crosslinked or non-crosslinked polymethyl (meth) acrylate is preferable. This is because this crosslinked or non-crosslinked polymethyl (meth) acrylate has good thermal decomposability, and carbon or the like is less likely to remain on the outer and inner walls of the hollow metal fine particles due to thermal decomposition.

A method for forming a spherical core material having the above-mentioned particle diameter from such an organic polymer is already known, and such a known method can be adopted in the present invention.

As a method for producing metal-coated polymer particles by forming a metal layer on a core material made of such an organic polymer, an ion sputtering method performed under special conditions under vacuum,
A method of forming a metal layer under a vacuum such as a CVD method (Chemical Vapor Deposite); and a method of forming a metal layer from a fine metal powder and a core material made of an organic polymer by using a dry blending microcapsule forming technique. Also, an electroless plating method can be adopted.

Among these methods, a good metal film can be obtained by a method such as an ion sputtering method or a CVD method for forming a metal layer under vacuum. However, these methods are special because they are operated under vacuum. It is not suitable as a method for mass-producing metal-coated polymer particles, which requires various devices. Further, as the particle diameter of the core material becomes smaller, it becomes difficult to form a uniform film on the surface of the core material, and in particular, it becomes difficult to form a metal layer of about 0.5 μm.

In the method utilizing the dry blending microencapsulation technique, a metal layer having a structure in which fine metal powder is arranged in one layer or multiple layers can be formed on the surface of the core material. This method requires the use of a surface modification device such as a hybridizer or mechanofusion. Then, by setting the operating conditions of these devices to suitable conditions, it is possible to form part or all of the metal layer. Further, by repeating this operation, the metal layer can be formed into multiple layers.

The electroless plating method is a method in which a core material is put in an electroless plating solution and a metal is laminated on the core material while stirring to form a metal layer. This electroless plating method is adopted. Thus, a large amount of a relatively thin and highly uniform metal film can be formed on the surface of the core material having a small particle size. Therefore, by adopting this electroless plating method, it is possible to inexpensively produce a large amount of metal-coated polymer particles. Moreover, a metal thin film layer having a thickness of about 0.05 μm can be easily formed, which is particularly suitable as a method for forming a metal layer in the present invention.

In general, a plating method which can be adopted as a method for forming a metal film by reducing and depositing metal ions in a solution on an object to be plated includes electroplating in which a metal ion is electrolytically deposited by an external electric power, in a solution. Of chemical plating for reducing and precipitating the metal ions of the solution with chemicals, and displacement plating for substituting and precipitating the metal ions in the solution by the object to be plated.
There are various types, and the above chemical plating and displacement plating are recognized as electroless plating methods. When the object to be plated is a core material made of an organic polymer as in the present invention, these electroless plating methods are suitable.

In the present invention, the metal layer formed by the electroless plating method is formed as follows, for example. The core material made of the above-mentioned organic polymer is subjected to the usual pretreatment and activation treatment in the electroless plating method. Depending on the method of this pretreatment and activation treatment, the state of metal deposition, the state of the deposited metal, etc. will change, and if these treatments are inadequate, the metal layer will become discontinuous, or when the core material is volatilized, the metal layer May not be able to maintain its form.

The core material thus treated has a room temperature to 90 ° C.
It is put into an electroless plating solution maintained at a temperature within the range of, and reacted for several minutes to 24 hours under stirring. That is, the reaction time and reaction conditions at this time are such that when the particle diameter of the core material is R μm and the thickness of the formed metal layer is D μm, the particle diameter of the obtained metal-coated polymer particles is 1 to 20 μm. Has a metal layer thickness D of 0.05 μm ≦ D, and D
/R≦0.25, and when the particle diameter of the obtained metal-coated polymer particles is more than 20 μm and 2 mm or less, it is set so as to satisfy the condition of 0.05 μm ≦ D ≦ 5 μm. .

Generally, when a metal film is formed on a flat object to be plated by electroless plating, a film having a considerable thickness can be formed. However, when attempting to deposit a metal by electroless plating on an adherend having a curvature on the surface (that is, particles used as a core material in the present invention), the thickness of the plating film formed is:
As the particle diameter of the core material becomes smaller, it tends to become thinner. This tendency is particularly remarkable when spherical fine particles are used as the core material, and when a core material having an average particle size of micron is used, the metal deposited on the surface of the core material is a continuous body of one granular metal. become. Even if an attempt is made to grow the thickness of the metal plating film, the structure is such that a few granular metals are projected on the surface of the particles. Therefore, in the present invention, the thickness D value of the metal layer is about 0.05 to several μm corresponding to the thickness of the granular metal layer thus formed (that is,
5 μm).

In the present invention, after the metal is deposited on the core material by, for example, electroless plating as described above, the drive blending microencapsulation technique is used to mechanically impact the metal layer. It is also possible to form a desired metal film by applying a shearing force or the like. further,
It is also possible to form a metal thin film layer on the surface of the core material by combining existing techniques, and then form a dissimilar metal film on the metal thin film layer by electroless plating to form a metal layer.

In the present invention, the metal-coated polymer particles produced as described above are shaped into a predetermined shape. When producing metal-coated polymer particles, it is possible to control the particle shape, average particle size, particle size distribution, tap packing density, etc. of the metal-coated polymer particles, and the metal-coated polymer particles produced in this manner are a dispersion medium. It has excellent dispersibility in water, has a low specific gravity, and is unlikely to settle in a dispersion medium.By utilizing such characteristics, press molding, injection molding, and lost metal powder metallurgy are used. In addition to adopting the wax method, extrusion molding,
Methods commonly used in plastic molding such as blow molding, extrusion blow molding, spinning, foam molding, and FR
Methods such as P molding, casting molding, cast molding, and molding by coating on a substrate can be adopted.
Further, the shaped body can take various forms such as a coated product, a film-shaped product, a sheet-shaped product, a plate-shaped product, a fibrous product, and a molded product having a complicated shape.

A binder may be used in this shaping. As the binder used here, various resins and volatile liquids capable of forming metal-coated polymer particles into a paste can be used.

Various resins can be used as the resin binder used here, but they are completely removed by heating in the sintering step, but some particles of the adjacent particles are removed to some extent in the step of removing the core material. It is preferable to use a resin that remains to the extent that it can be engaged with the joining force. Examples of such resins include waxes, polyethylene resins, polypropylene resins, ethylene-propylene resins, ethylene-vinyl acetate resins, polyethylene / poly (meth) acrylic resins, polystyrene resins, AS resins, ABS. Resin, polyvinyl chloride resin, vinyl chloride vinyl acetate resin, AN resin, (meth) acrylic resin, polybutadiene resin, SBR resin, NB
R resin, diene resin, polyacetal resin, polycarbonate resin, phenol resin, epoxy resin, polyester resin, polyether resin, urethane resin, polyimide resin, polyvinyl alcohol resin, cellulose resin, Examples thereof include polyvinylpyrrolidone resin, polyvinylcarbazole resin, benzoguanamine resin, urea resin, alkyd resin, and protein resin. Among these resins, waxes, polyethylene resins, polypropylene resins,
Ethylene / propylene resin, ethylene / vinyl acetate resin, (meth) acrylic resin, styrene / (meth) acrylic resin, diene resin, polyvinyl alcohol resin, polyvinyl acetate resin, cellulose resin, polyether -Based resins, polyester-based resins and epoxy resins can be completely removed by heating in the sintering process, and in the heating in the process of heating and removing the core material, a small amount remains and engages adjacent particles and pressurizes. Even if it is not carried out, a shaped body having good shape retention can be obtained, and thus it is particularly preferable as the resin binder in the present invention.

On the other hand, among such resins, when a resin having a high thermal decomposition temperature such as a phenol resin, a benzoguanamine resin, or a polyimide resin is used, the core material is completely heated by heating in the sintering step. Even if removed, the binder resin remains, and the adjacent particles are firmly engaged with each other, so that a shaped article having few cracks and good shape retention can be obtained. Furthermore, these binder resins can be removed by a known method, for example, the method disclosed in Japanese Patent Laid-Open No. 3-45,566, or part of the elements can be left.

Further, instead of the binder resin, an inorganic clay-like material or a binder resin mixed with an inorganic material can be used. Further, in the present invention, as a binder, in addition to the above resins, a liquid that does not affect the core material of the metal-coated polymer particles, which is a volatile liquid that facilitates pressure shaping of metallic polymer particles in a paste form. Can also be used. Examples of volatile liquids used herein are water; water-alcohol mixed liquids such as water-methanol mixed liquids, water-ethanol mixed liquids and water-isopropanol mixed liquids; hydrocarbon-based liquids such as paraffins. Glycols such as ethylene glycol and propylene glycol; polyhydric alcohols such as glycerin and mixed liquids with water; and plasticizers. As these volatile liquids, a water-alcohol mixed liquid is preferable. Most of such a volatile liquid is removed in the step of removing the core material from the metal-coated polymer particles.

The resin binder and volatile liquid may be used in combination. The binder as described above facilitates shaping of the metal-coated polymer particles, and the shaped body is used for facilitating the retention of its shape until the step of sintering or removing the core material. A small amount may be sufficient, or a large amount may be used, and usually 100 g of the metal-coated polymer particles,
It is added in the range of 0.5 to 100 g.

If necessary, the above-mentioned binder is added to the metal-coated polymer particles, and then the particles are shaped into a desired shape. The metal-coated polymer particles can be shaped under pressure or without pressure, whether or not the binder is used.

For example, in the case of pressurizing, a small amount of water-alcohol mixed liquid is added to the metal-coated polymer particles and uniformly mixed to prepare a slurry, and the slurry is usually added to
A shaped body of metal-coated polymer particles can be produced by applying a pressure of about 1 to 800 kg / cm ² , preferably about 0.1 to 600 kg / cm ² . Further, even when a binder is not used, a shaped body of metal-coated polymer particles can be produced by applying the same pressure as above.
Since the metal-coated polymer particles have the core material, the metal-coated polymer particles do not collapse even if they are shaped by applying high pressure as described above.

Further, since the metal-coated polymer particles having a relatively small particle size have a certain degree of cohesive force by themselves, such metal-coated polymer particles can be shaped into a predetermined shape without applying pressure. can do. Further, when the above binder, particularly a resin binder, is used, it can be formed into a predetermined shape without applying pressure.

In the present invention, the core material is removed from the metal-coated polymer particle shaped body thus shaped into a predetermined shape to produce a metal fine powder aggregate shaped body. For removal of the core material, a removal method by solvent extraction or a method of applying thermal energy to the core material to thermally decompose and remove the core material can be adopted.

Particularly in the present invention, it is preferable to remove the core material by a method of thermally decomposing it. When the above organic polymer is used as the core material, the heating temperature for decomposing and removing the organic polymer is such that the thermal decomposition rate of the organic polymer varies depending on the heating time, and the organic polymer should be gradually thermally decomposed and removed at a low temperature. It can also be removed by thermal decomposition at high temperature. Organic polymers have a typical decomposition temperature of 150 for organic materials.
It is effectively decomposed and removed at a temperature of not less than 0 ° C, preferably 200 to 400 ° C or more.

When the metal is deposited on the surface of the core material as described above, the particulate metal continuously grows while forming grain boundaries to form a thin metal layer. Therefore, the metal layer formed by the electroless plating method on the surface of the core material made of the organic polymer maintains its morphology by applying thermal energy to the core material organic polymer to disperse and volatilize it. can do. Even when the metal coating covers the core material relatively thickly, the metal layer is subjected to stress due to thermal expansion, and a part of the metal layer is destroyed, or the organic layer which is the core material is heavy. The rise of the internal pressure during decomposition and volatilization of the coalescence destroys a part of the metal layer to form an opening.

When the organic polymer which is the core material is removed by thermal decomposition, it is desirable to heat it in an inert atmosphere, for example, in a nitrogen stream so that the metal layer is not oxidized as much as possible.

The above is a description of the method of thermally decomposing the organic polymer that is the core material, but in the case of decomposing and removing the organic polymer by irradiating an energy ray such as an electromagnetic wave, the organic polymer is thermally decomposed under the same conditions. Can be disassembled. In particular, since the metal-coated polymer particles have an outer shell made of metal, the core material of the organic polymer can be effectively heated by using electromagnetic waves or the like.

When the organic polymer that is the core material is removed by solvent extraction, a solvent capable of dissolving the core material of the metal-coated polymer particles, for example, when the organic polymer is non-crosslinked polymethyl (meth) acrylate In, toluene, aromatic solvents such as xylene, ester solvents such as ethyl acetate, ketone solvents such as methyl ethyl ketone, polar solvents such as acetone, dioxane, tetrahydrofuran,
Alternatively, the organic polymer can be removed by immersing the metal-coated polymer particles in a solvent such as a mixed solvent thereof. However, when adopting this method, if the metal layer is too dense, the solvent does not reach the core material, or the solvent that reaches the core material cannot convey the organic polymer to the outside of the metal layer. Therefore, this method is a method of removing a core material from a metal-coated polymer particle having a metal layer having pores or a metal-coated polymer particle having a defect (that is, an opening) in the metal layer itself. As is highly effective.

In the metal fine particle aggregate-shaped body thus produced, hollow metal fine particles from which the core material has been removed from each of a large number of metal-coated polymer particles are engaged with adjacent fine particles to form a predetermined shape as a whole. It has a shaped form. Incidentally, each hollow metal fine particles may be maintained in a predetermined form by mutually engaging adjacent particles due to the cohesive force of the particles acting between the particles, or a small amount of particles remaining between the particles. Adjacent particles may be joined by the resin binder to maintain a predetermined shape. In addition to the hollow metal fine particles as described above, the metal fine particle aggregate-shaped body of the present invention may contain a fragment (metal layer slice) in which the hollow metal fine particles are crushed.

The porous metal sintered body of the present invention is a sintered body of the metal particle aggregate shaped body as described above, and at least a part of the hollow metal fine particles or the crushed material is fused to form a porous body. Is forming.

8 to 10 show SEM photographs of the porous metal sintered body of the present invention. 8-10, especially 9 and 1
As shown in 0, in the porous metal sintered body of the present invention, the hollow metal fine particles are fused with other adjacent particles while maintaining the same shape to form a porous body. This porous body has voids between the respective particles, and the metal fine particles have hollow portions, and the hollow metal fine particles also have voids communicating with the outside. Therefore, the porosity of the porous metal sintered body of the present invention is very high, and the porosity is usually 38-
It is in the range of 99.99%, preferably in the range of 50 to 99%. Therefore, the porous metal sintered body of the present invention has a very large contact area with a gas or a liquid. Moreover, this sintered body has the characteristic of being extremely lightweight. For example, the specific surface area of this porous metal sintered body is Ni
In the case of, the density is usually in the range of 0.9 to 8 m ² / g, and the apparent density is in the range of 9 × 10 ^{−4 to} 4.5 g / cm ³ .

This porous metal sintered body is obtained by heating the above-mentioned metal fine particle aggregate shaped body to a temperature which is 25% lower than the melting point of the metal forming the shaped body to a temperature lower than the melting point of the metal and sintered. It can be manufactured by The sintering time at the above temperature is usually 30 minutes to 4 hours, preferably 1 to 4 hours. This sintering is usually
It is performed in an oxygen-free atmosphere such as a nitrogen atmosphere (an atmosphere in which oxygen is substantially absent regardless of the pressure). Note that this firing can be performed under pressure or without applying any pressure.

In particular, it is preferable to carry out this sintering step continuously with the heating step of decomposing and removing the core material from the metal-coated polymer particles. As described above, the heat energy can be effectively used by continuing the heating step for removing the core material and the sintering step.

The thus-produced porous metal sintered body is subjected to chemical conversion treatment with chemicals, firing in a reducing gas or non-oxidizing atmosphere, etc., depending on the application in which it is used, The sintered metal surface can be modified and used.

The porous metal sintered body produced in this way has a very high porosity and a very large contact area with a gas or a liquid. Therefore, this porous metal sintered body is used as an oil-impregnated bearing material; a mold, a rolling tool, a cutting tool, a machine part, an electrical contact, a friction material, a filter, a magnetic part, an aircraft part, an automobile part, an abrasion resistant part; a conductor material, Resistance materials, contact materials, electrode materials, sealing materials, pyroelectric materials; microtube materials, dielectric materials, capacitor materials, piezoelectric materials, surface acoustic wave materials, high magnetic permeability materials, microwave materials,
Magnet materials, magnetostrictive materials; semiconductor materials, thermoelectric materials, photoelectric materials, electron emission materials; electromagnetic wave shielding materials, electrode materials for batteries, catalyst materials for chemical reactions, sensor materials; gas adsorbents, sound insulation materials, temperature insulation materials, etc. Can be effectively used as.

[0058]

EFFECTS OF THE INVENTION The porous metal sintered body of the present invention has a shape in which a large number of metal fine particles having hollow portions are shaped into a predetermined shape, and the shaped body is sintered. The surface extends not only to the surface of the metal fine particles but also to the inner wall surface of the hollow portion of the hollow metal fine particles. Therefore, this porous metal sintered body has a very high porosity, and the contact area per unit volume becomes very large. Further, since it is a sintered body of hollow metal fine powder, it has a low apparent density and is lightweight. Therefore, it is possible to obtain a sintered body having a high metal activity without performing a complicated operation such as manufacturing and sintering ultrafine powder of metal by a very special method like a conventional porous metal sintered body. it can.

The porous metal sintered body of the present invention having such excellent characteristics is obtained by shaping a large number of metal-coated polymer particles into a predetermined shape and then removing the core material. It can be manufactured very easily by producing a collective shaped body and sintering this shaped body.

[0060]

The present invention will now be described in more detail by showing examples of the present invention, but the present invention is not limited to these examples.

[0061]

Example 1 Production of metal fine powder aggregate shaped body As a core material, crosslinked polymethylmethacrylate fine particles (MR-7G, manufactured by Soken Chemical Co., Ltd.) having an average particle diameter of 7 μm were prepared, and the core material was electroless plated. After the usual pretreatment and activation treatment described in 1. above, this core material was subjected to Ni electroless plating treatment.

That is, 4000 ml of a reaction solution obtained by diluting a commercially available electroless plating solution by 5 times was placed in a plastic beaker and heated to hold at 50 ° C. To this reaction solution, 6.0 g of the core material activated as described above was added and reacted for 12 hours while stirring.

After the reaction, the Ni-plated fine particles were collected by filtration, and the fine particles were repeatedly washed with ion-exchanged water and dilute hydrochloric acid to obtain Ni-plated metal-coated polymer particles. The metal-coated polymer particles were dried with hot air for 6 hours in a dryer and then crushed with a ball mill. The crushed metal-coated particles were passed through a 75-mesh screen and the fraction passed through the 75-mesh screen was collected. The recovered amount was 11.3 g, the Ni deposition amount per 1 g of the core material was 0.88 g, and the average thickness of this plating layer was about 0.15 μm.

1 g of the Ni-plated metal-coated polymer particles was placed in an agate mortar, and several drops of a water / alcohol mixed medium were added and mixed well to prepare a slurry sample. This sample was pressure-molded with a tablet molding machine manufactured by Riken Seiki Co., Ltd. That is, one mirror surface plate is placed on the molding part inside the cylinder, and about 200 mg of the sample is placed on it so that the thickness is as uniform as possible, and then one mirror surface plate is placed on this sample, and the cylinder is placed over it. I put it on. After exhausting from the exhaust pipe of the molding machine with a vacuum pump for 15 minutes, pressurization (600 kg / cm ² ) was applied while continuing the exhaustion, and after 15 minutes, the pressure was released and the exhaust was stopped.

When the sample sandwiched between the mirror surface plates inside the cylinder was taken out, a disc-shaped metal fine powder aggregate shaped body was obtained.

[0066]

Example 2 Production of Porous Metal Sintered Body Crosslinked polymethylmethacrylate fine particles (MR-7G, manufactured by Soken Chemical Co., Ltd.) having an average particle diameter of 7 μm were prepared as a core material, and the core material was electroless plated. After the usual pretreatment and activation treatment described in 1. above, this core material was subjected to Ni electroless plating treatment.

That is, 4000 ml of a reaction solution prepared by diluting a commercially available electroless plating solution by 5 times was placed in a plastic beaker, and the temperature was raised and kept at 50 ° C. To this reaction solution, 6.0 g of the core material activated as described above was added and reacted for 12 hours while stirring.

After the reaction, the Ni-plated fine particles were collected by filtration, and the fine particles were repeatedly washed with ion-exchanged water and dilute hydrochloric acid to obtain Ni-plated metal-coated polymer particles. The metal-coated polymer particles were dried with hot air for 6 hours in a dryer and then crushed with a ball mill. The crushed metal-coated particles were passed through a 75-mesh screen and the fraction passed through the 75-mesh screen was collected. The recovered amount was 11.3 g, the Ni deposition amount per 1 g of the core material was 0.88 g, and the average thickness of this plating layer was about 0.15 μm.

1 g of the Ni-plated metal-coated polymer particles was placed in an agate mortar, and several drops of a water / alcohol mixed medium were added and mixed well to prepare a slurry sample. This sample was pressure-molded with a tablet molding machine manufactured by Riken Seiki Co., Ltd. That is, one mirror surface plate is placed on the molding part inside the cylinder, and about 200 mg of the sample is placed on it so that the thickness is as uniform as possible, and then one mirror surface plate is placed on this sample, and the cylinder is placed over it. I put it on. After exhausting from the exhaust pipe of the molding machine with a vacuum pump for 15 minutes, pressurization (600 kg / cm ² ) was applied while continuing the exhaustion, and after 15 minutes, the pressure was released and the exhaust was stopped.

When the sample sandwiched between the mirror surface plates inside the cylinder was taken out, a disc-shaped metal fine powder aggregate shaped body was obtained. The disk-shaped metal powder aggregate shaped body sample was placed in a crucible, and the crucible was inserted and held in an electric furnace preheated and kept at 400 ° C. under a nitrogen gas atmosphere for 2 hours.

After that, the temperature of the electric furnace is gradually raised to 1100 ° C.
Up to 50 ° C / 10 minutes at a heating rate of 30 minutes.
Hold for minutes, then cool to room temperature. The sample in the crucible retained a disk-like shape, and it was porous when the surface of the sample was observed by SEM. SEM of this sample surface
The photographs are shown in FIGS. It can be seen from these SEM photographs that the adjacent hollow metal fine particles are partially fused to form a porous body in the porous metal sintered body obtained.

The porosity of this porous metal sintered body is 92.
%, And the apparent specific gravity was 0.74 g / cm ³ .

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an example of a cross section of hollow metal fine particles of the present invention.

FIG. 2 is a scanning electron micrograph showing the state of the entire hollow metal fine particles.

FIG. 3 is a scanning electron micrograph showing a state of hollow metal fine particles in which some holes are formed in the Ni metal layer formed by a continuous body of the Ni metal plating layer.

FIG. 4 is a scanning electron micrograph showing hollow metal fine particles having through holes generated when the core polymer is decomposed and volatilized in a part of the continuous body of the Ni metal plating layer.

FIG. 5 is a scanning electron micrograph showing hollow metal particles in the lower part of the photograph in a state in which metal grain boundaries disappear in the Ni metal plating layer and a continuous body is formed in a mesh shape.

FIG. 6 is a scanning electron micrograph showing another state of hollow metal particles.

FIG. 7 is a scanning electron micrograph showing another state of hollow metal particles.

FIG. 8 is a scanning electron micrograph of a porous metal porous body of the present invention.

FIG. 9 is a scanning electron micrograph of the porous metal porous body of the present invention.

FIG. 10 is a scanning electron micrograph of the porous metal porous body of the present invention.

[Explanation of symbols]

 1 ... Hollow metal particles 2 ... Metal layer 3 ... Hollow part 4 ... Opening part

Claims (16)

[Claims] 1. The inside is hollow metal fine particles, the particle diameter of the hollow metal fine particles is in the range of 1 μm to 2 mm, and the thickness D of the metal layer forming the hollow metal fine particles and the hollow metal fine particles The diameter R of the hollow portion is 0.05 μm ≦ D and D / R ≦ 0.0 when the particle diameter of the hollow metal fine particles is 1 to 20 μm.
25, and the particle diameter of the hollow metal fine particles is 20 μm.
2 mm or less, the relationship of 0.05 μm ≦ D ≦ 5 μm is satisfied, and the hollow metal fine particle-containing metal particle group containing hollow metal fine particles having openings in at least a part of the metal layer has a predetermined shape. A metal fine powder aggregate shaped body formed by. 2. A metal-coated polymer particle shaped body obtained by shaping a large number of metal-coated polymer particles having a metal layer on the surface of a core material particle made of an organic polymer, and from the obtained organic polymer. A method for producing a metal fine powder aggregate shaped body, comprising removing the core material. 3. The metal fine particles according to claim 2, wherein a large number of metal-coated polymer particles are shaped into a predetermined shape under pressure or without pressure in the presence or absence of a binder. A method for producing a powder aggregate shaped body. 4. A metal-coated polymer particle shaped article is provided with thermal energy capable of thermally decomposing an organic polymer forming a core material of the metal-coated polymer particle, and the organic polymer is thermally decomposed. The method for producing a metal fine powder aggregate shaped body according to claim 2. 5. The method for producing a metal fine powder aggregate shaped body according to claim 2, wherein the application of the thermal energy is a heating operation. 6. The metal layer on the surface of the metal-coated polymer particles,
3. The metal fine powder aggregate shaped article according to claim 2, which is a metal film and / or a metal particulate continuous body formed by electroless plating on the surface of core material particles made of a thermally decomposable polymer. Production method. 7. The method for producing a metal fine powder aggregate shaped body according to claim 2, wherein the organic polymer has a spherical shape. 8. A plurality of metal-coated polymer particles are shaped into a predetermined shape in the presence of a binder under pressure or without pressure, and then the core material of the metal-coated polymer particles is removed, and at least one of the binders is removed. The method for producing a metal fine powder aggregate shaped body according to claim 2 or 3, wherein the part is left. 9. The inside is hollow metal fine particles, the particle diameter of the hollow metal fine particles is in the range of 1 μm to 2 mm, and the thickness D of the metal layer forming the hollow metal fine particles and the hollow metal fine particles are The diameter R of the hollow portion is 0.05 μm ≦ D and D / R ≦ 0.0 when the particle diameter of the hollow metal fine particles is 1 to 20 μm.
25, and the particle diameter of the hollow metal fine particles is 20 μm.
If it exceeds 2 mm and is less than 2 mm, the relationship of 0.05 μm ≦ D ≦ 5 μm is satisfied, and at least a part of the hollow metal fine particles having openings in at least a part of the metal layer or a crushed product thereof is fused. A porous metal sintered body characterized by the above. 10. The porous metal sintered body according to claim 9, wherein the porosity of the porous metal sintered body is in the range of 38 to 99.99%. 11. A metal-coated polymer particle shaped body obtained by shaping a large number of metal-coated polymer particles having a metal layer on the surface of a core material particle made of an organic polymer, And removing the core material to form a fine metal powder aggregate shape body, and then heating the fine metal powder aggregate shape body from a temperature 25% lower than the melting point of the metal forming the shape body to a temperature below the melting point. A method for producing a porous metal sintered body, comprising: 12. The method for producing a porous metal sintered body according to claim 11, wherein the sintering is performed in an oxygen-free atmosphere. 13. The method according to claim 1, wherein a large number of metal-coated polymer particles are shaped into a predetermined shape under pressure or without pressure in the presence or absence of a binder and then sintered. Item 11. A method for producing a porous metal sintered body according to item 11. 14. A metal-coated polymer particle shaped body is provided with heat energy capable of thermally decomposing an organic polymer forming a core material of the metal-coated polymer particle, and the organic polymer is thermally decomposed and removed. And sintering.
A method for producing a porous metal sintered body according to item. 15. The metal layer on the surface of metal-coated polymer particles is a layer formed by electroless plating on the surface of core particles made of a degradable polymer.
The method for producing a porous metal sintered body according to item 1. 16. The method for producing a porous metal sintered body according to claim 11, wherein the organic polymer has a spherical shape.