JPH11319530A - Method for dispersing conductive particle flocculate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the effective dispersion of a flocculate of conductive particles such as carbon black by emitting a high frequency electromagnetic wave to a flocculate of conductive particles in a medium, and further preferably applying at least either of an ultrasonic emission treatment or a rapid stirring treatment after the emission of the high frequency electromagnetic wave to perform the dispersion treatment. SOLUTION: When dispersing a flocculate of conductive particles which are difficult to disperse finely in a liquid e.g. carbon black, carbon fiber, metallic particle, metallic fiber or the like, the flocculate is dispersed by emitting a high frequency electromagnetic wave to the flocculate contained in a medium. The high frequency electromagnetic wave to be used ranges from micro waves of the giga hertz area to high frequency waves of the 10-100 giga hertz area. After the emission of the high frequency electromagnetic wave, either of a process to emit an ultrasonic wave or a process to stir rapidly or a combination of these processes is applied in arbitrarily selected order to achieve a further improved dispersion. In addition, the process to emit the high frequency electromagnetic wave may be employed after the ultrasonic emission pretreatment or the rapid stirring pretreatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dispersing agglomerates of conductive particles. More specifically, the present invention relates to a method for dispersing agglomerates of conductive particles which are difficult to finely disperse in a liquid such as carbon black, carbon fibers, metal particles, and metal fibers.

[0002]

2. Description of the Related Art The main uses of conductive particles such as carbon black are fillers for increasing elastic modulus and strength by being mixed with rubber or resin, and conductivity-imparting agents for imparting conductivity. Fillers used in such applications are:
The shape of the primary particles is spherical or fibrous, but many of them are agglomerated and aggregated. Alternatively, since the powder is scattered as it is, it is often granulated and used as a lump for the purpose of preventing the scattering.

[0003] When compounding these powder lumps (aggregates) with rubber or resin, particularly when compounding with rubber or resin latex or solution, a part of the powder remains in a lump without being dispersed,
Therefore, not only the desired effect cannot be obtained,
This also causes a significant reduction in the material strength, which is a major problem in the manufacturing process.

[0004] In particular, carbon black of the type classified as conductive carbon black has a problem that the breaking strength of the lumps is higher than that of carbon black for ordinary reinforcing use, and that poor dispersion is likely to occur. Therefore, if this can be effectively dispersed, extremely high conductivity can be obtained and a material having high reinforcing properties can be obtained, but it is generally difficult to obtain a material having a good dispersion state.

Various methods have been conventionally used for mixing powders, and the main methods are methods using a stirring blade, a ball mill, a shaker, an ultrasonic homogenizer, a kneader, a roll mill, and the like. In the method, agglomerated particles are hard to be broken due to strong cohesive force, and a mixed state in which conductive carbon black or the like is often insufficiently dispersed easily.

[0006] For example, the form of conductive carbon black is formed by fusing primary particles of 1 nm size partially by fusing.
Alternatively, aggregates called submicron-sized aggregates connected in branches are formed in some places, and the aggregates are physically aggregated to form micron to millimeter-sized agglomerates.

The aggregate and the agglomerate are combined to form a structure. The latter has a weaker cohesive force than the former, but because the aggregate is highly entangled like a thread and is less likely to be loosened, mechanical operations such as stirring are required. In the method using the shearing force, a part of the agglomerate still remains in a lump, causing poor dispersion.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for effectively dispersing aggregates of conductive particles such as carbon black.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by irradiating the conductive particle agglomerates in the medium with high-frequency electromagnetic waves, and more preferably by applying at least one of ultrasonic irradiation and high-speed stirring treatment and then performing dispersion treatment.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention is applied to agglomerates of conductive particles, particularly conductive carbon black agglomerates which are difficult to disperse due to the development of a structure, and are effective dispersions not found in other dispersion methods. It is effective. Examples of the conductive carbon black include special carbon blacks such as acetylene black and Ketjen black and vapor-grown carbon fibers.When these carbon blacks are effectively dispersed, high conductivity can be obtained even in a small amount. Applied to rubber and resin.

On the other hand, MT carbon black and FT carbon black used as fillers and reinforcing agents, carbon black for ink, general carbon fibers, etc. can of course be dispersed by the method of the present invention. In addition, since a sufficiently good dispersion state can be formed even by other stirring treatment or ultrasonic irradiation, the superiority of the method of the present invention is not particularly recognized.

Examples of the conductive particles other than carbon black include fine particles and fibers of metals such as copper, nickel and silver.

In the case of carbon-based particle agglomerates, it is about 1.
Since it has a specific gravity of about 8 to 2.1, when it is put into a medium such as water, alcohol, a hydrocarbon-based organic solvent, or an oligomer, it precipitates at the bottom of the vessel containing the medium. When placed in a high-frequency electromagnetic wave irradiation field of the used closed container, the aggregates are observed to be rapidly repelled in the medium, and gradually become smaller while moving around vigorously and irregularly. . Also, when water is added to copper powder having a particle size of about 2 to 10 μm and irradiated with high-frequency electromagnetic waves, as in the case of carbon black,
It is observed that the copper particles move violently and disperse.

Although the direction of repelling looks random, it is presumed that it depends on the environment of the irradiation field. On the other hand, when a high-frequency electromagnetic wave is applied to the carbon-based particle aggregates without a medium, sparks are locally observed and a phenomenon in which the carbon-based particles are scattered is observed.

In view of the above, the dispersion process when the high-frequency electromagnetic waves are irradiated on the conductive particle aggregates is that the medium near the surface is locally rapidly heated by the electromagnetic waves reflected by the conductive particle aggregates. , The instantaneous expansion force when the medium rapidly gasifies or the cutting of the agglomerated part due to rapid overheating,
It is considered that a mechanism for breaking the agglomerates into small pieces is taken.

As the high frequency electromagnetic wave, any of microwaves in the gigahertz range to high frequencies in the range of several tens to several hundreds of gigahertz can be used. The irradiation density varies depending on the type and concentration of the dispersion medium, but is about 0.01 to 5 Wh / g,
Preferably it is about 0.02-0.1 Wh / g.

Instead of irradiating high-frequency electromagnetic waves, ultrasonic irradiation or high-speed stirring using a colloid mill, homogenizer or the like does not achieve effective dispersion of carbon aggregates. It is effective to apply the methods in combination. Specifically, after irradiating high-frequency electromagnetic waves, ultrasonic irradiation,
A method of high-speed stirring or a method of applying both methods in an arbitrary order is effective for further increasing dispersibility. Alternatively, a method of irradiating high-frequency electromagnetic waves after ultrasonic irradiation or high-speed stirring processing may be adopted.

As the medium, water is preferably used from the viewpoint of no pollution and non-flammability, but other than this, an organic solvent such as alcohol and toluene, or an oligomer is used according to the purpose. In the case of an aqueous medium, a nonionic surfactant or an anionic surfactant or a dispersant such as polyvinyl alcohol is used in an amount of about 0.1 to 5%, preferably in order to increase the affinity between the aqueous medium and the conductive particles. Is about 1
Approximately 3% may be added for use.

For example, when a carbon-based aggregate is dispersed in an aqueous medium, about 1 to 20% by weight, preferably about 5 to 10% by weight
The carbon-based agglomerates added at a rate of て い る are initially settled at the bottom, but when they begin to be irradiated with high-frequency electromagnetic waves, they move around violently as if they are being vigorously stirred, and the lumps become smaller as the irradiation dose increases. Finally, an aqueous dispersion which does not precipitate even when the irradiation is stopped is formed. When about 10% by weight of Ketjen Black is added to the aqueous medium, a sharp increase in the viscosity of the aqueous dispersion is observed as the dispersion proceeds, so that the thixotropic property, that is, elasticity is exhibited. become. At the same time, when the DC electric resistance of the aqueous dispersion is measured, the DC electric resistance suddenly decreases in response to the sudden change in viscosity.

This means that the carbon-based agglomerates are loosened and dispersed in the aqueous medium in units of aggregates or small agglomerates, and they come into contact with each other in the medium, that is, carbon black having elasticity and conductivity. This indicates that the network structure has been formed. This network is formed with water interposed therebetween and has a very low strength, so that a static phenomena in which water gradually permeates when left standing is observed.

When the concentration of the aqueous dispersion is about 5% by weight or less, the state of the aqueous dispersion is exhibited during the stirring, but when the stirring is stopped, the dispersed carbon black reagglomerates, That is, flocculation occurs and a phenomenon of separation into water and the network structure portion of carbon black is observed.

The carbon black thus dispersed is dispersed in a liquid and formed into a sheet by a paper making method or the like, or rubber is coprecipitated with a polytetrafluoroethylene dispersion or other polymer latex. After compounding with resin and forming into a sheet or pipe shape,
As a highly conductive and flexible material, conductive composite materials,
It is effectively used as a catalyst carrier for gas phase reaction and liquid phase reaction, and as an electrode material for various batteries.

[0023]

According to the method of the present invention, an effective dispersion of agglomerates of conductive particles such as carbon black is achieved.

[0024]

Next, the present invention will be described by way of examples.

Example 1 A glass beaker having a capacity of 300 ml was charged with 200 ml of water and 5 g of acetylene black (specific gravity: about 1.9), and was subjected to an oven-type high-frequency electromagnetic wave generator (ER-250 manufactured by Toshiba) at a frequency of 2450 MHz.
Irradiated with high frequency electromagnetic wave of output 0.5KW. When irradiation starts, the precipitated carbon starts to move around in the water vigorously. The size of one carbon agglomerate breaks into several small pieces with its movement, and the small pieces become about 1-5 μm.
It became the size of. The DC electric resistance of the dispersion 10 minutes after irradiation was 360Ω.

Comparative Example 1 In Example 1, a high-speed rotating homogenizer (MX type manufactured by Nippon Seiki) was used instead of the high-frequency electromagnetic wave generator, and the number of rotations was 80.
After high-speed stirring at 00 rpm for 20 minutes, the DC electric resistance of the dispersion was 11000Ω.

Comparative Example 2 In Example 1, an ultrasonic generator (Branson Sonifier450, horn: 3/4 inch cylindrical type) was used instead of the high-frequency electromagnetic wave generator, and dispersion was performed after ultrasonic irradiation for 20 minutes. The measured DC electric resistance of the liquid was 3100Ω.

Example 2 In Example 1, 2 g of Ketjen Black was used in place of acetylene black. The DC electric resistance of the dispersion 10 minutes after irradiation with the high-frequency electromagnetic wave was 7000Ω.

Comparative Example 3 In Example 2, a high-speed rotating homogenizer (MX type manufactured by Nippon Seiki) was used instead of the high-frequency electromagnetic wave generator, and the number of rotations was 80.
After high-speed stirring at 00 rpm for 20 minutes, the DC electric resistance of the dispersion liquid was 10,000Ω or more.

Comparative Example 4 In Example 2, an ultrasonic generator (Bonson Sonifier 450, horn: 3/4 inch cylindrical type) was used instead of the high-frequency electromagnetic wave generator, and dispersion was performed after ultrasonic irradiation for 20 minutes. The measured DC electric resistance of the liquid was 13000Ω.

Example 3 A glass beaker having a capacity of 300 ml was charged with 200 ml of water, 0.2 g of a nonionic surfactant (Emulgen 210, Kao Corporation) and 2 g of acetylene black. Processed. The value of the DC electric resistance of the dispersion with respect to the dispersion processing time is shown by the curve (A) in the graph of FIG.

The graph of FIG. 1 shows the case where the high-frequency electromagnetic wave irradiation is performed, the high-speed stirring treatment is performed using the high-speed rotating homogenizer (B), and thereafter, the ultra-high-frequency stirring is performed using the ultrasonic generator. When sonicated (C)
The relationship between the DC electric resistance value of the dispersion liquid and the processing time is also shown.

[Brief description of the drawings]

FIG. 1 is a graph showing a DC electric resistance value of a dispersion liquid with respect to a dispersion processing time in Example 3.

Claims (6)

[Claims] 1. A method for dispersing conductive particle aggregates, comprising irradiating high-frequency electromagnetic waves to a conductive particle aggregate in a medium to perform a dispersion treatment. 2. The method for dispersing agglomerates of conductive particles according to claim 1, wherein the high-frequency electromagnetic waves are irradiated and then the ultrasonic waves are irradiated. 3. The method for dispersing conductive particle aggregates according to claim 1, wherein high-speed stirring is performed after irradiation with high-frequency electromagnetic waves. 4. The method for dispersing agglomerates of conductive particles according to claim 1, wherein after irradiation with the high-frequency electromagnetic wave, ultrasonic irradiation and high-speed stirring are performed in any order. 5. A dispersion treatment is carried out in an aqueous medium in the presence of a surfactant or a dispersant.
A method for dispersing an aggregate of conductive particles according to the above. 6. The method for dispersing agglomerates of conductive particles according to claim 1, wherein high-frequency electromagnetic wave irradiation is performed prior to ultrasonic irradiation or high-speed stirring.