JP5569196B2 - Method for producing metal porous thin plate and metal porous thin plate obtained by the production method - Google Patents

Description

  The present invention relates to a method for producing a metal porous thin plate and a metal porous thin plate obtained by the production method. More specifically, the present invention relates to a method for producing a very thin porous thin plate made of metal powder suitable for electrodes of various batteries such as a fuel cell and a lithium ion battery, and a metal porous thin plate obtained thereby.

The metal porous member is an essential member for the catalyst carrier and the fuel cell electrode.
As a method for producing a metal porous member used for these applications, there are conventional techniques of Patent Documents 1 and 2.

  The titanium powder sintered bodies of Patent Documents 1 and 2 are formed by storing spherical gas atomized titanium powder in a sintering container and then vacuum-sintering without applying pressure. In the example, a filter having a porosity of 37 to 44% is described, and in the example of Patent Document 2, a sintered body having 45 to 67% pores is described.

However, the above prior art has not considered at all obtaining a very thin porous body. Therefore, only a porous body having a considerable thickness was present.
By the way, when the porous body is extremely thin, for example, 0.5 mm or less, there are advantages such as a reduction in the thickness of the battery or a reduction in internal resistance when used in a battery or the like.

Therefore, various methods for thinning the porous body into thin films have been studied.
For example, in the first method, it has been studied to make a porous sheet having a certain degree of thinness and to apply a thin layer by applying pressure. However, in this method, since the pores are crushed, a high porosity cannot be realized at the expense of the porosity.

  In the second method, a method of applying a slurry containing metal powder to a foamed resin and sintering it to obtain a foamed metal and then cutting it thinly was studied. However, in this method, it is difficult to slice the sintered metal porous body because there is no suitable blade to make it possible, and it is not possible to cut it to an extremely thin thickness of 0.5 mm or less. It was.

JP 2002-66993 A JP 2002-317207 A

  In view of the above circumstances, the present invention provides a method for producing a very thin metal porous thin plate having a thickness of 0.1 to 0.5 mm and a metal porous thin plate obtained by the production method while being a porous body having an extremely high porosity. The purpose is to provide.

The method for producing a metal porous thin plate according to the first invention is a method for producing a metal porous thin plate having a thickness of 0.1 to 0.5 mm, and filling a foaming resin material with a curing aid filling. A curing step for curing the foamed resin material filled with the curing aid, a slicing step for slicing the cured foamed resin material into a thin film, a curing aid removing step for removing the curing aid from the sliced foamed resin thin film, An adhesion process for attaching metal powder slurry to the foamed resin thin film, a drying process for drying the foamed resin thin film coated with the metal powder slurry, a resin removal process for removing the foamed resin portion from the dried foamed resin thin film and leaving only the metal powder, A metal powder bonding process for bonding the formed metal powders to each other is sequentially performed.
The method for producing a metal porous thin plate according to the second invention is characterized in that, in the first invention, the metal powder is titanium.
The method for producing a metal porous thin plate according to a third invention is characterized in that, in the first invention, the metal powder is copper.
The method for producing a metal porous thin plate according to a fourth invention is characterized in that, in the first invention, the metal powder is aluminum.
The metal porous thin plate of the fifth invention is a porous thin plate produced by the manufacturing method of the first invention, formed of metal powder, and having a network structure formed by bonding metal powders together And is a thin plate having a thickness of 0.1 to 0.5 mm .

According to the first invention, since the foamed resin material is cured in the slicing step, it can be sliced to a very thin thickness of 0.1 to 0.5 mm. For this reason, a porous metal thin film having a high porosity in which the porous thin plate has a network structure and the inside of the skeleton itself is hollow can be made by sequentially executing the subsequent steps.
According to the second invention, a porous thin film made of titanium can be obtained, and can be used as a gas diffusion electrode of a fuel cell or a scaffold (scan field material) in cell culture.
According to the third aspect of the invention, since a copper porous thin film is obtained, it can be used as a negative electrode material for a lithium ion battery.
According to the fourth aspect of the invention, an aluminum porous thin film can be obtained, which can be used as a positive electrode material for a lithium ion battery.
According to the fifth shot bright, porous thin plate is a mesh structure, and so also skeleton itself inside is made of a metal powder having a A by high porosity hollow and is suitable for the electrode material. In addition, since the thickness is 0.1 to 0.5 mm, the battery can be thinned, the internal resistance can be reduced, the generation of Joule heat can be reduced, and the life can be extended.

It is process drawing of the manufacturing method of the metal porous thin plate M which concerns on this invention. It is an image figure of the foamed resin material R, and explanatory drawing of the hardening auxiliary agent filling process I. It is explanatory drawing of the slice process III and the hardening adjuvant removal process IV. It is explanatory drawing of the slurry adhesion process V and the drying process VI. It is explanatory drawing of the foamed resin thin film removal process VII and the metal powder coupling | bonding process VIII. It is explanatory drawing of the metal porous thin plate M which concerns on this invention.

First, based on FIG. 6, the schematic structure of the metal porous thin plate M of this invention is demonstrated.
As shown in the figure, the metal porous thin plate M of the present invention is a porous thin plate formed of metal powder, and has a network structure skeleton b formed by joining metal powders inside. The inside of the skeleton is a cavity h. The network structure means a sponge (sponge) -like structure in which a large number of continuous voids are formed. In the present invention, the skeleton b itself also has a cavity h. Such a porous structure of the present invention is called a hollow skeleton network structure.

In addition, it is one of the characteristics that the metal porous thin plate of the present invention is an ultrathin plate-like member having a thickness of 0.1 to 0.5 mm. The reason why such an ultra-thin plate can be formed depends on the manufacturing method described later. However, the ultra-thin plate has the following advantages when used for an electrode plate or the like.
a) In the case of a fuel cell • The stack becomes thinner.
・ Lower internal resistance.
・ Diffusion resistance becomes small.
b) Lithium ion battery • Joule heat generation is reduced and rapid charging is possible.
・ Lower internal resistance.
・ Stripping of active material hardly occurs and life is extended.

Below, the manufacturing method of the metal porous thin plate of this invention is demonstrated.
As shown in FIG. 1, the production method of the present invention comprises a first half step A for producing a foamed resin thin film and a second half step B for producing a metal porous thin plate M using the foamed resin thin film as a skeleton.
In the following process description, FIG. 1 is referred to for all processes, and FIGS.

First, the first half process A will be described.
In the first half process A, the foamed resin material R is used as a raw material. As shown in FIG. 2, the foamed resin material R is a resin material foamed to be porous. Further, any resin material can be used as long as it can be removed later by heating or the like.

As a resin material that becomes such an aggregate, for example, a polyester-based urethane resin, a polyether-based urethane resin, or the like can be used.
Moreover, there is no restriction | limiting in particular in a shape, The whole shape may be arbitrary shapes, such as a cube and a cylinder shape, and thickness may be thick. Furthermore, the length may be long.

(Curing aid filling process I)
As shown in FIG. 2I, the foamed resin material R is filled with a curing aid W. As the curing aid W, one that is cured by cooling water, paraffin, dry ice, or the like and dissolved by heating is used. Moreover, it may be one selected from various materials comprising a thermoplastic resin having a lower melting point than the urethane resin as the aggregate and a surfactant. That is, any material that cures and melts at a temperature lower than the melting point of the urethane resin as the aggregate may be used.
The method of filling the curing aid W is not particularly limited, and the foamed resin material R is immersed in the curing aid W such as water contained in the container, or the container filled with water is sealed and depressurized or pressurized. The way to do is taken. In short, it is only necessary that the curing aid W such as water enters the internal cavity of the foamed resin material R and is held there.

(Curing process II)
The foamed resin material R filled with a curing aid W such as water is cured. In order to cure, the curing aid W may be cooled below the temperature at which it begins to freeze. If the curing aid W is water, it may be frozen to ice.

(Slicing process III)
The foamed resin material R that has become hard due to the freezing of the curing aid W is sliced. Since the foamed resin material R in this process has high hardness and high rigidity, it can be sliced thinly. For this reason, it can be sliced to a thickness of 0.5 mm or less. This thinness is a thickness that cannot be sliced with the foamed resin material R that remains soft.
The blade to be sliced is arbitrary, and for example, a blade made of cemented carbide, ceramics, high-speed tool steel or the like can be used.
Through this step, a thin-film foamed resin material R cured with the curing aid W shown in FIG. 3III is obtained.

(Curing aid removal process IV)
In this step, the curing aid W is removed. The method of removing is arbitrary, but it is convenient to melt and dissolve away the curing aid W. For this purpose, the curing aid W may be heated above the temperature at which it begins to melt. When the hardening aid W is water, it is sufficient to melt frozen ice.
By this step, as shown in FIG. 3IV, there is obtained a foamed resin thin film F in which the curing aid W filled in the cavities H is eliminated and only the foamed resin material R remains. Of course, the cavity H remains a cavity, and the thickness t of the foamed resin thin film F is as thin as 0.5 mm or less as it is sliced.

Next, the second half process B will be described.
Before the adhesion step V in the second half step B, it is necessary to prepare a metal powder-containing slurry as preparation.
First, resin materials such as acrylic, urethane, polyethylene, polystyrene, butyral, etc. are melted with a solvent that evaporates at room temperature such as acetone, ethanol, toluene, etc. to make a liquid binder, and metal powder m is mixed with this binder to contain metal powder. Create a slurry.

  The resin material used for the binder hardens when the solvent evaporates, but it burns, evaporates and decomposes at high temperatures (for example, 100 ° C. or more and 500 ° C. or less) and has adhesiveness when dissolved in the solvent. If there is, there is no limitation in particular. A water-soluble resin such as water-soluble cellulose ether (CMC) or methyl cellulose (MC) can also be used. In this case, water can be used as a solvent.

Various metal powders can be used as the metal powder to be mixed with the metal powder-containing slurry without any particular limitation. Typical metals and their utilization forms are shown below.
Ti: PEFC (solid polymer fuel cell) gas diffusion material (electrode material)
Cu: negative electrode current collector of a lithium ion battery
Al: Positive electrode current collector of lithium ion battery
Ag: Gas diffusion electrode (soda electrolysis method), therapeutic electrode by drug electrophoresis
SUS: Purely manufactured electrode, corrosion resistant filter
Ni: Nickel metal hydride battery current collector, SOFC (phosphate fuel cell) anode side gas diffusion material

(Adhesion process V)
As shown in FIG. 4V, the foamed resin thin film F is immersed in the metal powder-containing slurry S containing the appropriate container 1. As described above, the foamed resin thin film F has a network structure skeleton b formed of a resin material such as urethane foam, polyethylene foam, or polystyrene, and a continuous void H is formed in the inside thereof. And 50% or more. For this reason, when the foamed resin thin film F is immersed in the metal powder-containing slurry S, the metal powder-containing slurry S enters the continuous void H, and the skeleton b of the foamed resin thin film F is surrounded by the metal powder-containing slurry S. As a result, the metal powder-containing slurry S adheres evenly to the outer peripheral surface of the foamed resin thin film F.
As long as the metal powder-containing slurry S can be attached to the foamed resin thin film F, any method other than the dipping method can be applied or sprayed. However, the metal powder-containing slurry S must be able to adhere to the outer periphery of the foamed resin thin film F evenly.

In this process V, since the very thin foamed resin thin film F is handled, it is preferable to use a measure that does not break during immersion.
For example, a method of protecting both the front and back surfaces of the foamed resin thin film F with a net is conceivable as a prevention of tearing, but any other method may be adopted as long as other methods are effective.

The resin material for forming the foamed resin thin film F has already been described. In particular, it is a substance that contains carbon and is insoluble in the solvent contained in the metal powder-containing slurry S, and burns, evaporates or decomposes at high temperatures. Those that do are preferred.
In particular, the resin material forming the foamed resin thin film F is one that burns, evaporates, and decomposes at 100 ° C. to 600 ° C., preferably 100 ° C. to 500 ° C., and more preferably 100 ° C. to 400 ° C. Is desirable. The reason for this is that when titanium is used as the metal powder, the passive film formed on the surface has a low activity up to about 400 to 600 ° C. and does not react with other substances. However, even if the resin material is decomposed to generate carbon, hydrogen, oxygen, etc., these substances can be prevented from diffusing inside the metal powder or reacting with the metal powder to form a compound. is there.
Moreover, when using aluminum as a metal powder, since melting | fusing point is 660 degreeC and sintering temperature is 500-600 degreeC, what is necessary is just to select the resin material which forms the foamed resin thin film F on the conditions similar to the above.
Furthermore, since metal powders other than titanium and aluminium are weakly reactive, they may be resin materials that do not satisfy the above conditions or resin materials that satisfy them.

(Drying process VI)
After the metal powder-containing slurry S has sufficiently penetrated into and adhered to the void H of the foamed resin thin film F, and the foamed resin thin film F is taken out from the metal powder-containing slurry S, the void H of the foamed resin thin film F is obtained. The excess of the metal powder-containing slurry S that has entered the inside is discharged from the foamed resin thin film F, and the remainder of the metal powder-containing slurry S remains attached to the surface of the skeleton b of the network structure in the foamed resin thin film F. Remains.
When the foamed resin thin film F is dried, a layer L containing the metal powder m is formed on the surface of the skeleton b as shown in FIG. Then, the layer L containing the metal powder m is also formed in a network structure.

(Resin removal step VII)
Next, the dried foamed resin thin film F is placed on a setter (sintering cradle) in a sintering furnace and heated to remove the resin material inside the skeleton b of the foamed resin thin film F. As a result, as shown in FIG. 5 (VII), a hollow skeleton porous plate in which the skeleton b itself has a cavity h and a large gap H is formed between the skeleton b and the skeleton b is obtained.

A substance such as the foamed resin thin film F becomes more active as it becomes finer. For example, in this step VI, if the foamed resin thin film F is thinned to about 0.2 mm, there is a disadvantage that it adheres to the setter.
Therefore, the material selection of the setter is important, and for example, stabilized zirconia, magnesia, quartz glass, molybdenum and the like are preferable because of low reactivity at high temperatures.
As a sintering furnace, a heating furnace using millimeter wave sintering is easier to use than a vacuum furnace with external electric heating. A general microwave oven (2.45GHz) has a long wavelength (about 12cm), and spark discharge occurs and cannot be heated. However, using internal heating of 30GHz electromagnetic waves (wavelength is about 1cm) will heat the metal selectively. This is because the setter does not reach a high temperature and only the foamed resin thin film F can be heated.
When the temperature in the sintering furnace is about 100 ° C or higher, that is, when the temperature exceeds the temperature at which the resin material burns, decomposes, and evaporates, the organic material that made up the resin material decomposes, and oxygen and hydrogen that were present in the organic material Is vaporized or combined with each other to form water vapor and discharged from the furnace. Also, the carbon present in the organic matter is combined with the oxygen present in the organic matter, becomes carbon dioxide and carbon monoxide, and is evaporated from the furnace.

  At this time, the carbon contained in the organic substance is not all bonded to oxygen and evaporated, but a part of the carbon becomes free carbon and remains on the surface of the metal particle. Then, since this free carbon functions as a binder that bonds the metal powder m to each other, a skeleton b of the metal structure is formed by the metal powder m. That is, since the metal powders existing in the layer L of the resin material are bonded in a state where they are arranged as they are, this metal structure has almost the same structure as the layer L of the resin material. That is, the metal structure is formed in a network structure, and the skeleton b of the network structure is in a hollow state.

(Metal powder bonding process VIII)
If heating is continued after the skeleton b of the metal structure is formed, the temperature in the sintering furnace further increases, and the skeleton b of the metal structure is also heated while maintaining the network structure. And when the temperature in a sintering furnace becomes high temperature, the activity of the surface of metal powder will become high, and metal powder will contact directly and will mutually couple | bond together. By this step, a high strength skeleton in which the metal parts constituting the skeleton outer skin as shown in FIG. 5 (VIII) are integrated is obtained. In addition, a small cavity in which a gap between the metal powders m remains also in the outer skin itself, which is a reason for obtaining a higher porosity.

The detailed reason for forming the skeleton b by direct contact with the metal powder is as follows.
When the metal powder is titanium, when the furnace temperature is 600 ° C. or higher, the activity of the passive film formed on the surface of the titanium powder becomes high, and it easily reacts with other substances. Then, oxygen in the titanium oxide reacts with free carbon existing on the surface of the titanium powder to become CO and CO ₂ to be separated from the titanium powder, and the separated CO and CO ₂ are removed from the vacuum furnace. . At the same time, when hydrogen remains in the titanium structure, a part of the free carbon reacts with the residual hydrogen to become hydrocarbon (HC), which is gasified and removed from the titanium structure. A part of free carbon diffuses into titanium powder.
Then, the titanium powder comes into direct contact with the metal titanium, mutual diffusion occurs between the metal titanium in contact with each other, and the adjacent titanium powder m is diffusion-bonded. Then, even if the free carbon that functioned as the binder disappears, the network structure having substantially the same structure as that of the layer L of the foamed resin thin film F is maintained with the titanium powder m alone. Then, with time, diffusion bonding of the titanium powder m proceeds, and a strong porous thin plate having a network structure skeleton formed of the titanium powder m is formed.
The reason for forming the skeleton b by high-temperature sintering is the same for metal powders made of copper or aluminum other than titanium.

In the above high-temperature sintering, it is preferable to use a millimeter-wave heat sintering apparatus.
For example, aluminum is a difficult-to-sinter material because it forms a stronger oxide film than titanium. In a general high vacuum (about 10 ⁻³ MP) external heating furnace, an ultra high vacuum (about 10 ⁻⁴ MP) is required to remove the oxide film, but 30 GHz class millimeter wave irradiation is performed. In the case of a heating furnace, the inside of the furnace becomes a reducing atmosphere (oxygen is released from the sample), so that the sintering proceeds without an ultrahigh vacuum.
In addition, 2.45 GHz, which is used for microwave ovens, is known for electromagnetic heating that causes internal heating of the material, but the wavelength is 12 cm and it is difficult to make the electric field distribution uniform. It cannot be heated. Also, the metal that is a conductor cannot be used because it sparks. On the other hand, if an electromagnetic wave having a single digit frequency of 28 GHz (wavelength 1 cm) is used, it is easy to uniformly heat the sample and no spark discharge occurs. Therefore, the fusion with the setter can be eliminated by the millimeter-wave irradiation heating sintering method, and it is possible to prevent breakage during sintering of a 0.2 mm thick sample.

Through the above steps, an ultrathin metal porous thin plate M having a hollow skeleton network structure made only of a metal structure and having a thickness of 0.5 mm or less is obtained.
And since this metal porous thin plate M is very thin, when this is utilized for an electrode etc., the miniaturization becomes possible.

The characteristics of the metal porous thin plate M obtained by the above production method will be further described.
Since the metal porous thin plate of the present invention has a hollow skeleton network structure as described above, it achieves the same porosity as urethane foam or the like, that is, a high porosity of about 80% to 95%. is there. For this reason, the gas diffusion performance requested | required of a battery becomes favorable.

  In the porous metal thin plate of the present invention, since the skeleton of the hollow skeleton network structure is formed by bonding metal powder, the structural strength is also strong, for example, even if it is extremely thinned to 0.1 to 0.5 mm, for example. It has shape retention to maintain the shape. Moreover, since it is a high purity metal sintered body, plastic deformation such as bending is possible, and the creep characteristics are also good. Therefore, it is easy to maintain the tightening force after being incorporated into the battery stack.

Further, since the skeleton itself of the hollow skeleton network structure is formed by bonding of metal powder, the conductivity is also excellent. Therefore, it can be used as an electrode for a fuel cell that also requires electrical conductivity.
In particular, if the skeleton is formed using a powder having a small particle size, for example, a powder having an average particle size of 50 μm or less, preferably an average particle size of 20 μm or less, even if the porosity of the entire metal porous thin plate is increased, The porosity of the skeleton itself can be reduced. In other words, the gap formed between the metal powders in the skeleton portion is reduced. Then, since the strength of the skeleton itself can be maintained high even when the porosity is increased, the strength reduction of the porous thin plate can be prevented even if the porosity is increased.

In the metal porous thin plate of the present invention, a skeleton having a network structure in which metal powder is bonded is formed, and a large number of continuous voids are formed between the skeletons. Of course, the width of the void can be freely adjusted without being limited by the size of the powder, and the void ratio can be about 80% to 95%. Moreover, in the case of the metal porous thin plate of the present invention, the smaller the average particle size of the metal powder, the greater the degree of freedom of the shape and arrangement of the skeleton of the network structure, so the average particle size of the powder should be reduced. In this case, the porosity can be further increased.
And, if the particle size of the metal powder is reduced, the porosity of the skeleton portion is reduced, but by reducing the porosity of the skeleton portion, the bond between particles is strengthened and the strength of the skeleton of the network structure can be increased. The strength of the metal porous thin plate can be increased while maintaining a high porosity. That is, it is possible to satisfy both the strength improvement and porosity improvement of the metal porous thin plate.

Examples of usable applications of the metal porous thin plate M are as follows.
PEFC (solid polymer fuel cell) gas diffusion material (electrode material)
Negative current collector of lithium ion battery
Positive current collector of lithium ion battery
Gas diffusion electrode (soda electrolysis method)
Therapeutic electrodes by electrophoresis of pharmaceuticals
Pure production electrode, corrosion resistant filter
Nickel metal hydride battery current collector, SOFC (phosphate fuel cell) anode side gas diffusion material

In addition to the above, the following utilization is also possible for the metal porous thin plate M made of titanium. Cell scaffold in cell culture in regenerative medicine
Space-making material (barrier film) for periodontal disease treatment

2 Mesh structure of base material m Titanium powder J Resin material L Layer of resin material J H

Claims (5)

A method for producing a metal porous thin plate having a thickness of 0.1 to 0.5 mm,
Curing aid filling process for filling the foamed resin material with a curing aid,
A curing step of curing the foamed resin material filled with the curing aid,
A slicing step of slicing the cured foamed resin material into a thin film;
A curing aid removing step for removing the curing aid from the sliced foamed resin thin film;
An adhesion process for attaching metal powder slurry to the foamed resin thin film;
A drying step of drying the foamed resin thin film coated with the metal powder slurry;
A resin removal step of removing the foamed resin portion from the dried foamed resin thin film and leaving only the metal powder;
A method for producing a metal porous thin plate, comprising sequentially performing a metal powder bonding step of bonding the remaining metal powders to each other. The method for producing a metal porous thin plate according to claim 1, wherein the metal powder is titanium. The method for producing a metal porous thin plate according to claim 1, wherein the metal powder is copper. The method for producing a metal porous thin plate according to claim 1, wherein the metal powder is aluminum. Manufactured by the manufacturing method of claim 1,
A porous thin plate formed of metal powder,
It has a skeleton with a network structure formed by bonding metal powders, and the inside of the skeleton is hollow,
A metal porous thin plate characterized by being a thin plate having a thickness of 0.1 to 0.5 mm .

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