JPH11329450A - Manufacture of sintered substrate for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-porosity sintered substrate by expanding a micro-capsule uniformly and sufficiently and dispersing it uniformly in nickel slurry, in a manufacturing method of the sintered substrate by mixing the thermally expansive micro-capsule in the nickel slurry. SOLUTION: A micro-capsule, which is expanded by being heated, and nickel powder are dispersed in a dispersion medium, and heated up to the temperature at which the micro-capsule is expanded, and then a thickner is added and mixed to thereby prepare slurry, and the slurry is applied on a metal core material, heated, dried and afterwards sintered in a reducing atmosphere. The micro-capsule can be expanded sufficiently and dispersed uniformly in the slurry by this method, therefore, the sintered substrate for an alkaline storage battery, having a high porosity and a uniform hole distribution, can be obtained. As a result, nickel hydroxide, used as active material, can be filled easily and in a larger quantity, to thereby enable to obtain an electrode having a large electric capacity density.

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 sintered substrate used as an active material holder in an electrode plate of an alkaline storage battery.

[0002]

2. Description of the Related Art Conventionally, a sintered substrate for an alkaline storage battery is coated on both sides of a nickel-plated metal core with a slurry obtained by mixing a thickener composed of nickel powder such as carbonyl nickel, water, and a resin such as methyl cellulose. It was manufactured by sintering in a reducing atmosphere after being applied and dried. Electrodes for alkaline storage batteries such as nickel-cadmium storage batteries and nickel-metal hydride storage batteries are manufactured by immersing this sintered substrate in a nickel nitrate solution and electrochemically or chemically forming nickel hydroxide, which becomes an active material in the pores of the sintered substrate. Is obtained by filling. By filling a large amount of the active material, the electric capacity of the electrode is increased. Therefore, various methods have been proposed for increasing the amount of pores for filling the active material, that is, increasing the porosity of the sintered substrate.

As a method of increasing the porosity, there has been proposed a method of adding microcapsules to a slurry, whose shell walls are softened by heating and expanded by the vapor pressure of the contained hydrocarbon (Japanese Patent Laid-Open No. 58-1983). 169773). In the drying process after applying the slurry to the metal core material, the microcapsules in the coating film expand due to heat, and the portion where the microcapsules existed in the subsequent sintering process becomes voids,
The porosity of the sintered substrate can be increased. This method of increasing the porosity by using hollow microcapsules can increase the porosity with a smaller amount of resin compared to the case of adding a solid resin ball or the like, and the carbon remaining in the substrate after sintering The amount can be reduced and the price is also advantageous.

However, when the sintered substrate manufactured by the above-mentioned conventional manufacturing method expands the microcapsules during drying, the viscosity of the slurry coating increases as the drying proceeds,
There is a problem in that the skeleton of the nickel powder is formed by the resin serving as the thickener, and the microcapsules in the coating film cannot freely expand. In order to solve the problem, using microcapsules having a softening point lower than the boiling point of water of 100 ° C., by allowing steam to exist on the slurry surface during heating, the microcapsules can be dried without drying the applied slurry. A method of inflating has been proposed (Japanese Patent Publication No. 5-771).
No. 49). In this method, the microcapsules cannot be uniformly expanded due to temperature variations during heating and drying and the temperature distribution in the substrate after coating, and it is difficult to obtain a sintered substrate having a uniform pore distribution. In addition, since the softening point of the microcapsules is limited to 100 ° C. or less, if the temperature of the substrate is raised to about 150 ° C. in the drying step after expansion, the softened point is too low, so that the microcapsules that have undergone angular expansion may shrink. As a result, a sufficient hole-forming effect could not be obtained.

[0005] In order to solve the problem of sufficiently expanding the microcapsules, a method has been proposed in which the microcapsules which have been expanded in advance by heating are mixed with nickel powder and a thickener to form a slurry (particularly). JP-A-2-276160). In this method, since the microcapsules are expanded in advance by heating, the softening point of the microcapsules is not limited to 100 ° C. or lower. However, the specific gravity of the microcapsules after being expanded is as extremely small as about 0.02 to 0.2, and it is very difficult to handle because they are easily suspended in the air. If high shear is applied during slurry kneading to increase this dispersibility, the microcapsules have already expanded and the shell wall has become thin, so they will not be able to withstand the shear and will break, resulting in a sufficient pore-forming effect. I couldn't.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, expands the microcapsules sufficiently and uniformly, has a good dispersibility in the slurry, and has a sufficient pore formation because it does not crack. It is an object of the present invention to provide a method for producing a sintered substrate for an alkaline storage battery, which can provide an effect.

[0007]

In order to solve the above-mentioned problems, a method of manufacturing a sintered substrate for an alkaline storage battery according to the present invention comprises: a shell containing a low boiling hydrocarbon; A step of dispersing the expanding microcapsules and the nickel powder in a dispersion medium, heating the dispersion medium to a temperature at which the microcapsules expand, and then adding and mixing a thickener to prepare a slurry; The method is characterized in that the method comprises a step of applying the obtained slurry to a metal core material, drying by heating, and sintering in a reducing atmosphere. Here, in the step of dispersing the microcapsules and the nickel powder in the dispersion medium, it is preferable to first disperse the microcapsules in the dispersion medium and then add and disperse the nickel powder. Since the present invention expands the microcapsules by heating the dispersion medium in which the microcapsules and the nickel powder are dispersed in the absence of the thickener, the microcapsules can be sufficiently expanded. In addition, since the microcapsules and the nickel powder are dispersed in advance, a slurry in a uniform dispersion state can be obtained without applying high shear after adding the thickener.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail by preferred embodiments. First, isobutane was encapsulated as a low-boiling hydrocarbon, and microcapsules having a particle size of 10 to 20 μm and comprising a shell wall mainly composed of acrylonitrile were produced. After 200 g of the microcapsules were dispersed in 10 kg of water serving as a dispersion medium, 10 kg of carbonyl nickel powder was further charged and kneaded with a planetary mixer.
The microcapsules at this time are not expanded and have a specific gravity of about 1.
1, which is larger than the specific gravity after expansion of 0.02 to 0.2, so that it is less likely to float in the air and is easy to handle.
In addition, since the microcapsules are not expanded at the time of dispersion, the difference in specific gravity from the nickel powder is smaller than that after the expansion, and can be easily dispersed. Further, even if the microcapsules and the nickel powder are kneaded with a high shear until they are uniformly dispersed, the shell walls of the unexpanded microcapsules do not break because the shell walls are sufficiently thick. Here, when the microcapsules and the nickel powder are put into a dispersion medium at once and kneaded, the aggregation of the microcapsules may remain and the dispersion may be non-uniform. By dispersing the microcapsules first in the dispersion medium as described above, the microcapsules are more uniformly mixed with the nickel powder.

Next, the microcapsules and the nickel powder were sufficiently uniformly dispersed in water, and then placed in a hot-air dryer at 150 ° C. and dried. At this time, there is no thickener such as methylcellulose on the surface of the microcapsules, and even if there is nickel powder in the surroundings, the skeleton of the nickel powder does not solidify, so the microcapsules expand freely. can do. That is, even if it is dried, it expands, so that the dryer can be freely selected, such as an infrared type or a hot air type, and there is no need to introduce steam. Observation of the resulting dry powder with an optical microscope revealed that the microcapsules were uniformly dispersed between the nickel powders.
In order to examine the state of expansion of this microcapsule, 10
When the particle diameter of zero microcapsules was measured with an optical microscope, the average particle diameter was 40 μm, and the average expansion ratio of the particle diameter was 2.7 times, confirming that the microcapsules were sufficiently expanded.
Since the microcapsules in this dry powder are uniformly dispersed between the nickel powders, even if the specific gravity of the expanded microcapsules themselves is light, they do not easily float in the air, Is easy.

[0010] To this dry powder, 12 kg of a thickener consisting of methylcellulose and water was added and kneaded. At this time, since the microcapsules are uniformly dispersed between the nickel powders, a uniformly dispersed slurry can be easily obtained without kneading with high shear. Therefore, the microcapsules that have expanded and the shell wall has become thinner are present in the slurry without cracking. This slurry was applied to a metal core material whose surface was nickel-plated, and dried with a hot-air dryer at 150 ° C. At this time, since the microcapsules have already expanded, there is no need to allow water vapor to exist on the slurry surface, and a dryer can be freely selected, such as an infrared type or a hot air type. Even if there is some temperature distribution, since the thickener methylcellulose exists around the microcapsules, there is no possibility that the swelling will expand further and the pore distribution of the sintered substrate will be uneven. When the dried film was buried with an epoxy resin and polished, and the cross section was observed with an optical microscope, the expanded microcapsules were uniformly distributed in the film, and no cracked or withered microcapsules were found. The softening temperature of the shell wall of the microcapsule is about 130 ° C., and the substrate does not crack or shrink even if the temperature of the substrate rises to 150 ° C. during drying. Therefore, the porosity after sintering does not decrease. As described above, the softening temperature of the microcapsules is not limited to those having a boiling point of water of 100 ° C. or less, and can be freely selected according to the drying temperature.

The dried film was heat-treated at about 1000 ° C. in a reducing atmosphere containing hydrogen to obtain a sintered substrate. This sintered substrate has a nickel portion having a thickness of about 300 μm on one side and a porosity of about 88%, which is 7% compared to a porosity of 81% when a slurry without microcapsules is used. Increased.

For comparison, the same microcapsules 20
After dispersing 0 g in 12 kg of a thickener composed of methylcellulose and water, 10 kg of carbonyl nickel powder was added and kneaded with a planetary mixer to prepare a slurry, and this slurry was applied to a metal core material whose surface was nickel-plated. And dried with a hot air dryer at 150 ° C. In order to examine the state of expansion of the microcapsules at this time, when the particle diameter of 100 microcapsules present in the dried coating film was measured with an optical microscope, the average particle diameter was 15 μm, and the average expansion ratio of the particle diameter was 15 μm. Was one-time and hardly expanded. This is because methylcellulose is present on the surface of the microcapsules, and the viscosity of the slurry coating film is increased by drying and the skeleton of the nickel powder is solidified, so that the microcapsules cannot expand freely. The dried coating film is placed in a reducing atmosphere containing hydrogen for about 1000
Heat treatment was performed at ℃ to obtain a sintered substrate. This sintered substrate has a nickel portion having a thickness of about 300 μm on one side and a porosity of about 82%, which is 1% as compared with a porosity of 81% when a slurry without microcapsules is used. Only increased.

For further comparison, 200 g of the same microcapsules were pre-expanded at 150 ° C., dispersed in 12 kg of a thickener composed of methylcellulose and water, and then 10 kg of carbonyl nickel powder was charged and kneaded with a planetary mixer. did. The microcapsules after expansion were easily suspended in the air due to low specific gravity and were difficult to handle. Further, even if the microcapsules were dispersed in the thickener prior to the nickel powder, the microcapsules floated on the upper portion because of their low specific gravity, and a uniform dispersion state could not be obtained.
When the nickel powder is charged and kneaded with a planetary mixer, if the shear is low, the microcapsules do not crack but have poor dispersibility. That is, there were places where microcapsules and nickel powder were partially large or small. When the shear was increased to improve the dispersibility, microcapsules in the slurry were cracked and withered. Apply this slurry to a metal core material with nickel plating on the surface,
It was dried with a hot air dryer at 150 ° C. and heat-treated at about 1000 ° C. in a reducing atmosphere containing hydrogen to obtain a sintered substrate. This sintered substrate has a thickness of about 300 μm on one side and a thickness of about 84 μm.
Porosity of 3% compared to porosity of 81% when using a slurry without microcapsules.
Only increased. This is presumably because the microcapsules in the slurry were cracked or withered, so that a sufficient pore-forming effect could not be obtained.

Conventionally, there are many known techniques for increasing the porosity by using microcapsules. However, since all of these techniques have been used to collectively knead microcapsules, nickel powder, and a thickener, slurry has been produced. It has been difficult to achieve both a sufficient and uniform expansion of the capsule and a uniform dispersion in the slurry. In the present invention, the microcapsules are dispersed in a dispersion medium together with the nickel powder, and the microcapsules are expanded by heating in the absence of a thickening agent. Can be done. Further, since the microcapsules and the nickel powder are dispersed in advance, there is an advantage that a slurry in a uniform dispersion state can be obtained without applying high shear after adding the thickener.
Such a technique has never been reported before.

As described above, the present invention disperses nickel capsules and microcapsules containing low-boiling hydrocarbons, whose shell expands due to the vapor pressure of the contained hydrocarbons by heating, in a dispersion medium. After heating to the temperature at which the microcapsules expand, a thickener is added and mixed to prepare a slurry, the slurry is applied to a metal core material, dried by heating, and sintered in a reducing atmosphere. In order to manufacture a sintered substrate for an alkaline storage battery, the microcapsules can be sufficiently expanded and uniformly dispersed in the slurry, so that a sintered substrate for an alkaline storage battery having a large porosity and a uniform pore distribution can be obtained. can get. As a result, nickel hydroxide, which is an active material, can be easily filled because of many pores, and the electric capacity of the electrode is increased, so that a large-capacity alkaline storage battery can be formed.
In addition, since the porosity is increased, the gap into which the electrolyte enters is increased, so that the liquid is easily diffused, and the rapid charge / discharge characteristics of the battery are also improved.

In the above example, the microcapsules composed of shell walls mainly composed of acrylonitrile are selected, but the material is not limited thereto, and vinylidene chloride-based or methacrylic resin-based materials can be used. The material of the microcapsules is preferably a material that is completely thermally decomposed in the sintering step and does not leave residual carbon in the sintered substrate. In the above example, microcapsules having a particle size of 10 to 20 μm are used, but microcapsules having a particle size after expansion of 1 to 100 μm can be used. Microcapsules having a small particle size of less than 1 μm do not achieve a large pore-forming effect merely by entering into the gaps between nickel particles. Also, 100
Microcapsules having a size of more than μm are not preferable because the pores formed in the sintered substrate are too large and the strength of the substrate is weakened, or an invalid cavity in which the active material does not enter in the subsequent filling step is not preferable. Although water is used as the dispersion medium, any liquid that does not affect the expandability of the microcapsules and has good dispersibility may be used, and an organic solvent such as alcohol can also be used. In the above example, the drying temperature for expanding the microcapsules was set to 150 ° C., but may be any temperature higher than the softening temperature of the microcapsules, and the expansion ratio can be controlled by changing the temperature and the processing time. The powder after the drying treatment does not need to be completely dried. If the microcapsules are sufficiently expanded, there is no problem even if the dispersion medium remains.

[0017]

As described above, according to the present invention, the microcapsules can be sufficiently expanded and uniformly dispersed in the slurry, so that the porosity is large and the pore distribution is uniform. A bonding substrate is obtained. As a result, nickel hydroxide as an active material can be easily and more filled, so that an electrode having a large electric capacity density can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Kaida 1006 Kadoma Kadoma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] A step of dispersing nickel powder and microcapsules in which a low-boiling-point hydrocarbon is encapsulated and whose shell expands due to the vapor pressure of the enclosed hydrocarbon by heating;
After heating the dispersion medium to a temperature at which the microcapsules expand, a step of adding and mixing a thickener to prepare a slurry, and applying the obtained slurry to a metal core material, heating and drying, and reducing A method for producing a sintered substrate for an alkaline storage battery, comprising a step of sintering in a neutral atmosphere. 2. The method according to claim 1, wherein the step of dispersing the microcapsules and the nickel powder in the dispersion medium comprises first dispersing the microcapsules in the dispersion medium and then charging and dispersing the nickel powder. Of manufacturing a sintered substrate for an alkaline storage battery.