JPH097607A - Manufacture of metal porous body - Google Patents

Abstract

PURPOSE: To manufacture a useful metal porous body as an electrode base board for an alkaline secondary battery or the like. CONSTITUTION: After a binder resin is applied to a skeleton surface of a porous resin core body, a mixed powder comprising a metal powder and a carbon powder is directly applied thereto before the resin is hardened by drying and an organic resin component is reduced to ashes by electric Ni-plating method and by performing heat treatment in an unoxidizing atmosphere before the electric Ni-plating. Ni and Fe are better for metal power. Therefore, a useful metal porous body can be obtained without passing through a complicated process as an electric base board for an alkaline secondary battery or the like which has a desired strength characteristic and excels in quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal porous body mainly used for an electrode substrate of an alkaline secondary battery such as a nickel-cadmium battery, a nickel-zinc battery and a nickel-hydrogen battery.

[0002]

2. Description of the Related Art Lead-acid batteries and alkaline batteries are used as storage batteries used as various power sources. Among them, the alkaline storage battery has been widely used for various portable devices, and the large type for industrial purposes because it is expected to have high reliability and can be made compact and lightweight. In this alkaline storage battery, zinc, iron, hydrogen, etc. are targeted as the negative electrode in addition to cadmium. However, as the positive electrode, an air electrode, a silver oxide electrode, and the like are partially taken up, but in most cases, it is a nickel electrode. The characteristics were improved from the pocket type to the sintered type, and it became possible to further seal and expand the applications.

However, in the ordinary powder sintering method, when the porosity of the substrate is 85% or more, the strength is significantly lowered, so that there is a limit to the filling of the active material, and therefore, there is a limit to increase the capacity of the battery. Therefore, as a substrate having a higher porosity of 90% or more, a foamed substrate or a fibrous substrate has been picked up and put into practical use instead of the sintered substrate. As a method for producing such a porous metal substrate having a high porosity, Japanese Patent Application Laid-Open No. S5-5200 is known.
There are a method by a plating method disclosed in JP-A-7-174484 and a method by a sintering method disclosed in JP-B-38-17554. In the plating method, carbon powder or the like is applied to the skeleton surface of a foamed resin such as urethane foam to perform a conductive treatment, and Ni is electrodeposited thereon by an electroplating method, after which the foamed resin and carbon are eliminated, The method is to obtain a metal porous body.
On the other hand, in the sintering method, slurry metal powder is impregnated and applied on the skeleton surface of foamed resin such as urethane foam, and then heated to sinter the metal powder.

[0004]

As described in the prior art, the application of the metal porous body as the electrode plate for a battery makes a great contribution to the high capacity of the battery. However,
In the production of a metal porous body by a plating method as disclosed in JP-A-57-174484, it is necessary to apply carbon as a conductive treatment for electroplating a porous resin core, which is necessary in the production process. Anything is eventually burned out, and is not necessary as a porous metal body. Therefore, carbon coating for conductive treatment not only increases the cost as a product, but also may affect the quality aspect due to carbon residue,
The improvement is desired. In addition, Japanese Examined Japanese Patent Publication No. 38-1755
Although there is no problem as described above in the production of a porous metal body by a sintering method as disclosed in Japanese Patent Publication No. 4, but it is a complicated step such as a step of slurrying metal powder and applying it, or a sintering step. There are problems that it is difficult to obtain desired strength characteristics and the manufacturing cost is high.

[0005]

In order to solve the above problems, the present invention provides a method for producing a metal porous body, which comprises applying a binder resin to the skeleton surface of a porous resin core,
Before the resin is dried and cured, a mixed powder of metal powder and carbon powder is directly applied and electroplating is performed.

In the present invention, instead of the carbon conductive treatment of the conventional plating method, the conductive treatment with a mixed powder of metal powder and carbon powder is performed. In the conductive treatment method using the mixed powder of the metal powder and carbon powder of the present invention, a method of directly coating the metal powder on the porous resin core body coated with the binder is used in order to improve the conductivity.

Here, as a method for applying the binder resin to the porous resin core, the porous resin core is impregnated in a liquid obtained by mixing the binder resin and water or a diluent such as an organic solvent, and then rolling. It is possible to use a method of removing the excessively adhered material by a method such as the above, or a method of spraying the above liquid onto the porous resin core body by a spray or the like. Further, as the method of directly applying the metal powder, a method of spraying the metal powder on the porous resin with an air gun or a method of rocking the porous resin core in the metal powder can be used.

According to the method of directly applying the mixed powder as described above, in the conventionally used method of applying the slurry in which the metal powder and the binder resin are kneaded, the periphery of the metal powder is covered with the resin component. Therefore, the conductivity between the powders is deteriorated, while the surface of the porous resin core body coated with the binder resin can be uniformly covered with the mixed powder, and thus good conductivity can be obtained. Further, the metal powder used here can serve as the main skeleton of the metal porous body which is the final product, and does not burn all of it like carbon conductive treatment.

Further, by using a mixed powder with carbon powder instead of the metal powder alone, the carbon powder is inserted between the metal powders as a form of adhesion to the porous resin core, so that a gap between the metal powders is formed. Since it is filled with, the conductivity can be further improved as compared with the case of using a metal alone. Therefore,
The carbon powder used here is preferably a relatively fine powder having an average particle size of 10 μm or less, and more preferably an average particle size of 5 μm or less. Further, as the type of carbon, natural graphite, artificial graphite, carbon black or the like can be used. Further, as an effect of mixing the carbon powder, there is an effect that the amount of metal to be attached can be easily controlled. For example, in the case of a mixed powder having an average particle size of Fe powder of 40 μm and an average particle size of natural graphite powder of 5 μm, the relationship is as shown in FIG. Usually, the metal porous body of the present invention is used as a battery electrode substrate of an alkaline battery or the like, but in that case, the weight per unit area of the metal porous body has a great influence on the battery performance, so that it can be controlled accurately. Is important. However, when the metal powder alone is adhered to the porous resin core by the above method, the adhered amount is almost uniquely determined by the particle size of the metal powder, so it is not possible to strictly control the adhered amount. It will be quite difficult. Then, the present inventors have found that, for example, as shown in FIG. 1, the amount of Fe powder coated on the porous resin core can be controlled by the amount of carbon powder to be mixed.

Next, an Ni coating is formed by electric Ni plating to obtain a porous metal body. In addition, the porous resin core, the binder resin and the like can be removed by preferably performing heat treatment in a non-oxidizing atmosphere after the electric Ni plating.

Further, in the present invention, heat treatment is performed in a non-oxidizing atmosphere at the stage of directly applying the mixed powder consisting of the metal powder and the carbon powder to burn off the organic components such as the porous resin core and the binder resin. Then, a method for obtaining a porous metal body is also provided by forming a Ni film by electroplating Ni after that. This method eliminates the need for heat treatment after Ni plating by removing the organic components before forming the Ni film, so avoiding a decrease in strength or a decrease in conductivity due to diffusion of the metal powder and Ni metal during heat treatment. Is possible. Further, since the sintering of the metal powders progresses, the conductivity can be improved.

The metal powder is preferably Ni.
Alternatively, Fe is used. This is because when the Fe powder is used, the strength of the porous metal body can be improved, and at the same time, a large amount of inexpensive powder can be obtained.

Further, the amount of carbon powder is 2 wt% of metal powder.
% Or less, which has a carbon content of 2 wt%
This is because if it exceeds, there is a problem that the electrical resistance of the metal porous body finally obtained increases.

[0014]

【Example】

Example 1 Polyurethane foam having a thickness of 2.5 mm and about 50 pores per inch was made of acrylic resin 60 wt% and water 40.
After impregnating the binder resin liquid mixed with wt%, the excess impregnated coating portion was removed by a squeeze roll to prepare a binder-coated porous resin core.

Next, Fe powder having an average particle diameter of 55 μm and natural graphite powder having an average particle diameter of 5 μm are 99.2 in weight ratio (%):
A mixed powder that was uniformly mixed at a ratio of 0.8 was prepared. Next, the mixed powder was directly sprayed onto the porous resin core body by an air gun, and the conductive treatment was performed by drying in the air at 150 ° C. for 5 minutes. The coating amount of Fe powder at this time was 180 g / m ² , and the electric resistance was 10 m in width.
m and length 100 mm were 25Ω. This sample is designated as A.

As a comparative example, a slurry liquid of 50 wt% Fe powder, 10 wt% acrylic resin, and 40 wt% water was prepared, and polyurethane foam was impregnated into the slurry liquid, and the excess impregnated coating was removed with a squeezing roll. A porous resin core body coated with Fe powder was prepared. At this time, the coating amount of Fe powder was 400 g / m ² , and the electric resistance was 1
It was 0 mm and the length was 100 mm, and it was 250 kΩ. This sample is designated as B. Samples A and B were plated with Ni in a watt bath for electric Ni plating at a current density of 10 A / dm ² . In Sample A, a plating film was uniformly formed on the entire surface, and 200 g / m ² of Ni was plated.
Ni-plated sample in a hydrogen stream at 1000 ° C for 5
Heat treatment was performed for minutes to obtain a porous metal body. This sample is C
And On the other hand, in Sample B, since the electric resistance was high, Ni was plated only on the electrode connection portion, and a uniform Ni plating film could not be obtained.

Example 2 Polyurethane foam having a thickness of 2.0 mm and about 40 pores per inch was prepared by using 60 wt% of phenol resin and 4 parts of water.
A binder resin liquid mixed with 0 wt% was spray-coated to prepare a porous resin core body to which the binder was applied. Next, a mixed powder was prepared by uniformly mixing Ni powder having an average particle size of 6 μm and artificial graphite powder having an average particle size of 1 μm at a weight ratio (%) of 99.4: 0.6. Next, the porous resin core was shaken in this mixed powder to apply Ni powder, and then dried at 150 ° C. in the atmosphere for 10 minutes. The coating amount of Ni powder at this time was 250 g / m ² ,
The electric resistance was 25Ω at a width of 10 mm and a length of 100 mm. Ni plating was performed on this sample at a current density of 10 A / dm ² in a watt bath for electric Ni plating,
A Ni film of 0 g / m ² was formed. 700 ° C in the atmosphere, 5
After heat treatment for 5 minutes, further in a hydrogen stream at 1000 ° C. for 5
Heat treatment was performed for a minute to obtain a metal porous body. This metal porous body is referred to as Sample D.

Example 3 Polyurethane foam having a thickness of 2.5 mm and about 50 pores per inch was prepared by using 60 wt% of phenol resin and 4 parts of water.
After impregnating the binder resin liquid mixed with 0 wt%, the excess impregnated coating component was removed with a squeeze roll to prepare a binder-coated porous resin core.

Next, an Fe powder having an average particle size of 70 μm and a natural graphite powder having an average particle size of 5 μm were used in a weight ratio (%) of 98.6:
The porous resin core was shaken in a mixed powder that was uniformly mixed at a ratio of 1.4, then dried in the atmosphere at 150 ° C. for 5 minutes, and coated with 300 g / m ² of Fe powder. I put on my clothes. Next, after heat-treating at 1200 ° C. for 10 minutes in a hydrogen stream to burn off the urethane foam and the phenol binder resin, Ni plating is performed at a current density of 10 A / dm ² in a Watt bath for electric Ni plating, and 300 g / m ² Ni film was formed. Let this sample be E.

Example 4 Tensile strength of porous metal sample C, D and E,
Table 1 shows the results of measuring elongation and electric resistance.

[0021]

[Table 1]

From the results shown in Table 1, according to the manufacturing method of the present invention, it is possible to obtain a porous metal body having good characteristics.

[0023]

According to the present invention, a metal porous body useful as an electrode substrate for an alkaline secondary battery or the like can be obtained as a product having desired strength characteristics and excellent quality without complicated steps. it can.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of carbon powder and the amount of iron powder attached.

Claims (3)

[Claims] 1. After applying a binder resin on the surface of a skeleton of a porous resin core, and then directly applying a mixed powder of a metal powder and a carbon powder before the resin is dried and hardened, an electric Ni plating is performed. A method for producing a porous metal body, comprising: 2. After coating a binder resin on the skeleton surface of a porous resin core and then directly coating a mixed powder consisting of metal powder and carbon powder before the resin is dried and hardened, in a non-oxidizing atmosphere. A method for producing a porous metal body, characterized in that the organic resin component is burned down by heat treatment, and then electroplating with Ni is performed. 3. The method for producing a metal porous body according to claim 1, wherein the metal powder is Ni or Fe.