JPH09936A - Method for producing polyolefin-coated carbon carrier - Google Patents

Abstract

(57) [Abstract] [Purpose] In the conventional production of a carbon support coated with polyolefin, since heat drying is used to dry the obtained carbon support, particle agglomeration proceeds and the electrode characteristics of the obtained electrode deteriorate. There was a drawback that it would end up. An object of the present invention is to provide a method capable of preparing electrode particles having a uniform composition and a small diameter without advancing the aggregation of the particles when the electrode particles are produced using a solvent. [Structure] A polyolefin and a carbon carrier are mixed in a solvent capable of solvating the polyolefin, and after cooling, the solvent is removed by spray drying to form a uniform film of the polyolefin on the carbon carrier. Substantially the minimum unit of polyolefin formed by solvation is maintained as it is by spray drying and is supported on the carbon support in a uniform and fine particle state.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polyolefin-coated carbon carrier which is useful as an intermediate for a fluorinated polyolefin-coated carbon carrier which is a network substrate of an electrochemical cell such as a phosphoric acid fuel cell, and a method for producing the same. The present invention relates to a method for producing a fluorinated polyolefin-coated carbon carrier and a gas diffusion electrode using a carbon carrier, and more particularly to a method for producing the carbon carrier and the like, which can form the coating more uniformly.

[0002]

2. Description of the Related Art The gas diffusion layer of an electrochemical cell such as a fuel cell comprising a catalyst layer and a gas diffusion layer in contact with the catalyst layer is, for example, carbon black and water repellent polytetrafluoroethylene (hereinafter referred to as PTFE). ) Is used after applying or press-bonding the mixture of the fine powder of (1) or after the PTFE is adhered to the carbon paper. However, the gas diffusion layer requires a large amount of PTFE in order to maintain the gas supply ability for a long time, and as a result, the pores between the carbon black particles are blocked by the PTFE, leading to a reduction in the gas supply ability. As a result, the performance may be deteriorated when used for a battery or the like.

On the other hand, the catalyst layer has a function as a gas flow passage and an electrolyte flow passage, and the reaction gas supplied from the gas diffusion layer diffuses in the gas flow passage in the catalyst layer and is in contact therewith. It is designed to be dissolved in an electrolytic solution to carry out an electrode reaction on a catalyst in the electrolytic solution. However, if the electrolytic solution infiltrates into the gas flow passage in the catalyst layer due to long-term operation and the gas supply ability is lowered, the cell performance is extremely lowered. If the amount of the water repellent agent is increased in order to avoid this, it becomes difficult for the electrolytic solution to enter the catalyst layer, the catalyst cannot participate in the reaction, and the battery performance is also deteriorated.

In order to solve these drawbacks, the present applicants impregnate and support a polymer compound dispersion liquid such as polyethylene (PE) on the surface of a carbon black (CB) carrier or the like,
A method has been proposed in which the polymer compound is fluorinated after the solvent is volatilized, and the carrier is coated with a fluorinated polymer compound (JP-A-2-298523). This method is excellent as a method for producing a water-repellent treated carbon black carrier, but it is relatively difficult to dissolve the polymer compound into a completely uniform dispersion liquid, and moreover, Since the polyethylene particles cannot be made so fine, there is a drawback that the surface coating of PE / CB becomes uneven. If the fluorinated polymer compound layer formed on the carrier can be made into a more uniform thin film, it becomes possible to manufacture a battery or the like having higher activity.

In addition to the above, the present applicants also proposed a method in which polyethylene fine particles and carbon black particles are uniformly mixed and heat-treated to melt the polyethylene so that the polyethylene is diffused on the carrier surface and then fluorinated. (Japanese Patent Application 5-80
No. 228). However, in this method, the contact between the polyethylene particles and the carrier is point contact, and even if the polyethylene melted by heating spreads on the carrier, it does not disperse completely uniformly, and depending on the conditions, part of the carrier surface may be polyethylene. There is a defect that it is not covered with and unevenness occurs.

To further overcome this drawback, the Applicants have found that in order to more uniformly disperse and form the polyolefin coating of the polyolefin-coated carbon support, which is the precursor of the fluorinated polyolefin-coated carbon support, A method has been proposed in which a carbon carrier is mixed in a solvent capable of solvating the polyolefin above the melting point of the polyolefin, and then rapidly cooled to support the polyolefin in a fine state on the carbon carrier (Japanese Patent Application No. 6- No. 332459). By this method, a polyolefin-coated carbon carrier which is more uniform and has a smaller particle size than the conventional polyolefin-coated carbon carrier can be produced. However, this carbon carrier does not have completely satisfactory performance, and a higher-performance polyolefin-coated carbon carrier is required. ing.

[0007]

An object of the present invention is to meet this need, and to provide a method for producing a carbon carrier coated with a polyolefin having a finer particle size and a uniform particle size distribution than the polyolefin-coated carbon carrier obtained by the prior art. It is also intended to do.

[0008]

According to the present invention, a polyolefin and a carbon carrier are mixed in a solvent capable of solvating the polyolefin at a melting point of the polyolefin or higher, and after cooling, the solvent is removed by spray drying, A method for producing a polyolefin-coated carbon carrier by forming a uniform coating of polyolefin on the carbon carrier, wherein the polyolefin-coated carbon carrier produced in this manner is fluorinated polyolefin to produce a fluorinated polyolefin-coated carbon carrier. Further, the carbon support coated with fluorinated polyolefin can be used as an electrode material for a gas diffusion electrode.

Hereinafter, the present invention will be described in detail. In the present invention, in order to avoid the suppression of homogenization due to the small number of contact points between the carbon carrier and the polyolefin in the above-mentioned prior art, the polyolefin particles are made as small as possible in the initial contact stage of the carbon carrier and the polyolefin. The number of contact points is increased to make the final polyolefin distribution more uniform and thin, and spray drying is adopted instead of heat drying which tends to cause aggregation and particle growth of the carbon carrier. Examples of the carbon carrier that can be used in the present invention include simple carbon such as carbon black, activated carbon, and amorphous carbon, and it is preferable to use carbon black.

Polyolefins that can be used in the present invention include polyethylene and polypropylene, which have a relatively small molecular weight and do not lose fluidity, and it is preferable to use polyethylene. For the miniaturization of polyolefin,
In the present invention, the polyolefin is solvated in a solvent.
The completely solvated polyolefin, especially polyethylene, exists in the solvent in a substantially single fiber state, and the state of the single fiber is considered to be the minimum existence unit of the polyolefin.
Therefore, if the polyolefin is deposited on the carbon support in this state, the finest and most uniformly dispersed polyolefin-coated carbon support can be produced.

The solvent capable of solvating the polyolefin varies depending on the type of the polyolefin, but in the case of polyethylene, for example, n-hexane, n-pentane, n-heptane, dioxane and chloroform are used. Put a polyolefin such as polyethylene and a carbon carrier in this solvent, and under a high temperature above the melting point of the polyolefin and at a high pressure to prevent boiling of the solvent (normally 3.5 to 30 kg / cm ² ). So, when heat-treated, the polyolefin is almost completely solvated (of course,
This heat treatment temperature must be kept below the critical temperature of the solvent. For example, in the case of polyethylene, its melting point is 110 ° C.
To the critical temperature of 235 ℃).

Then, the mixed solution of the solvated polyolefin and the carbon carrier is cooled, preferably by quenching by a method such as water cooling or charging into a condenser, so that the solvated polyolefin maintains a fine state on the adjacent carbon carrier. It precipitates as it is. Since the above-mentioned solvated polyolefin is the minimum existing unit, the solvated polyolefin deposited on the carbon carrier is also the minimum existing unit, and therefore has the maximum contact point, and the subsequent melting causes the polyolefin to stay on the carbon carrier. The polyolefin thin film formed by diffusing is the most uniform.

However, these polyolefins are intertwined with each other, and if they are heated and dried as they are, the single fiber-like polyolefins agglomerate or particles grow and harden due to the heat applied, and the particle size is increased in the subsequent pulverization step or the like. It becomes difficult to obtain uniform carbon carrier particles. Therefore, in the present invention, the solvent is removed by spray-drying the polyolefin-coated carbon carrier suspended in the solvent after cooling the above-mentioned finest and most uniformly dispersed polyolefin-coated carbon carrier and then filtering and heating and drying. . This spray drying is a method of evaporating and drying the solvent by spraying particles having a small diameter portion such as a nozzle suspended in a solvent at a relatively high speed. A polyolefin-coated carbon support is obtained.

The atomization may be performed by using an inert gas such as nitrogen gas, that is, the organic solvent suspension of the polyolefin-coated carbon carrier is passed at a relatively high speed through a small diameter passage such as a nozzle. At this time, since the nozzle has a small diameter, the organic solvent passes as fine droplets. Therefore, the carbon carrier passes in the form of relatively small clusters, not in an aggregated state. At that time, the amount of the organic solvent that composes the individual droplets is small, and the organic solvent is easily volatilized by being sprayed from the nozzle, the organic solvent is removed without performing a special drying treatment, and the carbon carrier aggregates. Almost never.

The diameter of the nozzle is about 0.1 to 2 mm,
The pressure at which the suspension passes through the nozzle at a rate of about 1 to 10 g / min, preferably 0.5 to 1.5 kg / cm.
Apply ² . Also, the inlet side of the nozzle is relatively hot, for example 60
To 160 ° C., and the organic solvent suspension is diffused through the nozzle into the atmosphere at room temperature or an inert gas atmosphere such as nitrogen gas to volatilize the organic solvent without performing a drying operation, that is, passing through the nozzle. The preparation operation and the drying operation of the carbon carrier particles can be simultaneously performed only by performing the above. It is desirable that the particles thus prepared have a particle size of 1 to 50 μm.

The polyolefin-coated carbon carrier thus produced is converted into a fluorinated polyolefin-coated carbon carrier by fluorinating if necessary.
The conversion may be carried out according to a conventional technique, and for example, the fluorination reaction proceeds only by positioning the polyolefin-coated carbon support in a fluorine gas atmosphere diluted with an inert gas. Of course, it is possible to increase the reaction rate by heating a little. In this fluorinated polyolefin-coated carbon carrier, the fluorinated polyolefin thin film has maximum uniformity as in the above-mentioned polyolefin-coated carbon carrier. Therefore, the fluorinated polyolefin-coated carbon carrier may be used in a fuel cell or other electrochemical cell by a wet method such as a filtration transfer method or a method in which the carrier is pasted and printed, or a dry method such as using a screen and suction. When configured as a catalyst layer and / or a gas diffusion layer of an electrode gas diffusion electrode, the uniformly distributed fluorinated polyolefin almost completely covers the carbon black particles of the catalyst layer or gas diffusion layer, and thus the operation is continued for a long time. However, the catalyst performance hardly deteriorates due to the permeation of the electrolytic solution,
Long life is secured.

[0017]

EXAMPLES Next, examples relating to the method for producing the polyolefin-coated carbon carrier according to the present invention will be explained, but the present examples do not limit the present invention.

Example 1 Carbon black (Denka Black) and polyethylene (U1tZex manufactured by Mitsui Petrochemical Co., Ltd.)
Pellet-like sample) was weighed so as to be 68:32 (weight ratio), mixed, and then poured into n-hexane to form a slurry.

The polyethylene was sufficiently solvated by stirring at 170 ° C. under a high temperature and high pressure condition of 11 kg / cm ² for 10 hours, and then rapidly cooled by water cooling. Then, this n-hexane suspension of carbon black coated with polyethylene was put into the inside of a spray having a nozzle inner diameter of 0.7 mm and the inside heated to 100 ° C., and the spray pressure was 1 kg / cm ² , and the liquid feeding rate was 5 g / min. When sprayed in the air, the particle size is 7 to 13 μm
Polyethylene-coated carbon black particles were obtained.
The particle size distribution is shown in the graph of FIG. The horizontal axis of the graph of FIG. 1 is a logarithmic scale. Next, the polyethylene-coated carbon black particles were fluorinated in an argon gas containing 10% fluorine gas to obtain fluorinated polyethylene-coated carbon black particles.

[0019] Initially, when polyethylene bearing before the heat treatment, and the specific surface area of the carbon black after spray drying are each ^{74m 2 / g, 34m 2 /} g and 30 m ² / g, the initial ratio of before and after heat heat treatment Reduction rate for surface area is -54
% And -60%. 2 to 5 are micrographs showing the surface texture of carbon black particles in a series of manufacturing steps, FIG. 2a is a 50,000 times micrograph of untreated carbon black particles, and FIG.
FIG. 3a is a 50,000-times micrograph of carbon black particles after coating with polyethylene, and FIG.
FIG. 4a is a 50,000 times micrograph of the carbon black particles after heat treatment, FIG. 4b is the same 500 times micrograph, and FIG. 5a is a 50,000 times micrograph of the fluorinated carbon black particles.
FIG. 5b is also a 5 × magnification micrograph.

[0020]

[Comparative Example 1] The same operation as in Example 1 was carried out until quenching by water cooling, and then the polyethylene-supported carbon black obtained by filtration was crushed and placed in a rotary kiln in a nitrogen atmosphere.
Heat treatment was performed at 190 ° C. for 1 hour to obtain polyethylene-coated carbon black. The particle size distribution is shown in the graph of FIG. The horizontal axis of the graph of FIG. 6 is a logarithmic scale. Initially, the specific surface area of the carbon black when loaded with polyethylene before heat treatment and after heat treatment was 74 m ² / g and 34, respectively.
m ² / g and 28 m ² / g, and the rate of decrease with respect to the initial specific surface area before and after the heat treatment was −54% and −62%. Comparing the graphs of FIG. 1 and FIG. 6, the particle size distribution of the carbon black of FIG. 1 has a uniform and fine particle size with a normal distribution centered at a particle size of about 10 μm, whereas in FIG. Is about 80 μm, the particle size is coarse and the particle size distribution is not uniform.

[0021]

INDUSTRIAL APPLICABILITY According to the present invention, a polyolefin and a carbon carrier are mixed in a solvent capable of solvating the polyolefin at a melting point of the polyolefin or higher, and after quenching, the solvent is removed by spray drying, and then the carbon carrier is applied. Forming a uniform coating of polyolefin is a method for producing a polyolefin-coated carbon carrier (Claim 1). The solvated and quenched polyolefin deposited is the smallest possible unit of existence, with virtually no polyolefin below this size. Therefore, the number of sites at the contact point between the solvated polyolefin supported on the carbon support and the carbon support is also close to the limit value. Therefore, the polyolefin-coated carbon support produced by melting this and depositing it on the carbon support. The efficiency of contact between the above polyolefin and the carbon support is maximum, and the polyolefin is distributed on the carbon support with the maximum degree of dispersion.

Thus, the polyolefins of the polyolefin-coated carbon support prepared by the solvation have the highest possible homogeneity, which level is of course unattainable in the prior art. Furthermore, in the present invention, since spray drying is used without using conventional heat drying to remove the solvent, there is no aggregation or growth of particles caused by the heat drying, and the above-mentioned possible highest uniformity is considered. Maintained.

By carrying out the spray drying under the conditions specified in claim 2, a particularly desirable polyolefin-coated carbon carrier can be obtained. Solvents that can be used to solvate the polyolefin include n-hexane, n-pentane,
There are n-heptane, dioxane, chloroform and the like (claim 3), and it is preferable to use n-hexane. Thus, the homogeneity of the polyolefin of the polyolefin-coated carbon support produced according to the present invention is at the highest possible level.

Therefore, the homogeneity of the fluorinated polyolefin of the fluorinated polyolefin-coated carbon carrier (claim 4) obtained by fluorinating the polyolefin-coated carbon carrier is at the highest level possible. The above-mentioned polyolefin-coated carbon carrier and fluorinated polyolefin-coated carbon carrier according to the present invention finally constitute a catalyst layer which constitutes a gas diffusion electrode of an electrochemical cell such as a fuel cell and / or a catalyst which is a constituent element of the gas diffusion layer. Often used as particles (Claim 5), the gas diffusion electrode has the highest homogeneity of the fluorinated polyolefin coating the catalyst particles, resulting in the highest water repellency and longest life and The highest gas permeability based on water can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the particle size distribution of the polyolefin-coated carbon black obtained in Example 1.

FIG. 2a is a 50,000 times micrograph of untreated carbon black particles, and FIG.

FIG. 3a is a 50,000 times micrograph of carbon black particles after coating with polyethylene, and FIG.

FIG. 4a is a graph of carbon black particles 5 after heat treatment.
10000x micrograph, Figure 4b is also 5x100 micrograph.

FIG. 5a is a 50,000 times micrograph of carbon black particles after fluorination, and FIG.

FIG. 6 is a graph showing the particle size distribution of the polyolefin-coated carbon black obtained in Comparative Example 1.

[Procedure amendment]

[Submission date] August 7, 1995

[Procedure Amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

[Fig. 2]

[Figure 3]

FIG. 4

[Figure 5]

FIG. 6

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 7/00 B05D 7/00 K H01M 4/88 H01M 4/88 H

Claims (5)

[Claims] 1. A polyolefin and a carbon carrier are mixed in a solvent capable of solvating the polyolefin at a temperature not lower than the melting point of the polyolefin, and after cooling, the solvent is removed by spray drying to obtain a uniform coating of the polyolefin on the carbon carrier. A method for producing a polyolefin-coated carbon carrier, which comprises forming 2. A polyolefin-coated carbon carrier having a particle size of 0.1 to 100 μm, a spray temperature of 60 to 160 ° C., and a spray pressure of
The method according to claim 1, wherein the boiling point of the organic solvent is 0.5 to 1.5 kg / cm ² , and the boiling point of the organic solvent is 160 ° C. or less. 3. The solvent is n-hexane, n-pentane,
The production method according to claim 1, which is n-heptane, dioxane, or chloroform. 4. A uniform film of a polyolefin on a carbon carrier prepared by mixing a polyolefin and a carbon carrier in a solvent capable of solvating the polyolefin at a melting point of the polyolefin or higher, cooling and then removing the solvent by spray drying. And fluorinating the polyolefin in a fluorine gas atmosphere to convert the fluorinated polyolefin into a fluorinated polyolefin. 5. A uniform film of a polyolefin on a carbon carrier prepared by mixing a polyolefin and a carbon carrier in a solvent capable of solvating the polyolefin at a melting point of the polyolefin or higher, cooling and then removing the solvent by spray drying. And further fluorinating the polyolefin in a fluorine gas atmosphere to convert it into a fluorinated polyolefin,
A method for producing a gas diffusion electrode, comprising using the fluorinated polyolefin-coated carbon carrier as a constituent particle of a catalyst layer and / or a gas diffusion layer to form a gas diffusion electrode.