JP3840801B2 - Method for dispersing conductive particle agglomerates - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for dispersing conductive particle agglomerates. More specifically, the present invention relates to a method for dispersing conductive particle agglomerates that are difficult to finely disperse into liquids such as carbon black, carbon fibers, metal particles, and metal fibers.
[0002]
[Prior art]
Main applications of conductive particles such as carbon black are fillers for blending with rubber or resin to increase the elastic modulus and strength, and conductivity imparting agents for the purpose of imparting conductivity. In fillers used for such applications, the primary particles have a spherical or fibrous shape, but many of them are aggregated into a lump. Alternatively, since it is scattered as it is in powder form, it is often granulated and used as a lump for the purpose of preventing it.
[0003]
When blending these powder lumps (aggregates) into rubber or resin, especially when blended into rubber or resin latex or solution, some of them remain in a lump without dispersing, so the desired effect Not only cannot be obtained, but also causes a significant reduction in material strength, which is a major problem in the manufacturing process.
[0004]
In particular, the type of carbon black classified as conductive carbon black has a problem that the fracture strength of the lump is larger than that of carbon black for normal reinforcement, and a dispersion failure is likely to occur. Therefore, if this can be dispersed effectively, extremely high conductivity can be obtained, and a highly reinforcing material can be obtained, but it is generally difficult to obtain a material having a good dispersion state.
[0005]
Various methods have been conventionally used for mixing powders, and the main method is a method using a stirring blade, a ball mill, a shaker, an ultrasonic homogenizer, a kneader, a roll mill, etc., but these methods are agglomerated. The force is strong and the particle agglomerates are not easily broken, and conductive carbon black or the like often tends to be in a mixed state with insufficient dispersion.
[0006]
For example, in the form of conductive carbon black, primary particles of 1 nm size are partly fused to form aggregates called submicron size aggregates that are connected in the form of threads or branches, and this aggregate is further formed. The gates physically aggregate to form micron to millimeter size agglomerates.
[0007]
Aggregates and agglomerates are called structures, and the latter is less cohesive than the former, but the aggregates are highly entangled like yarns and difficult to loosen. In the method, a part of the agglomerates still remains in the form of lumps, causing poor dispersion.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide an effective method for dispersing agglomerates of conductive particles such as carbon black.
[0009]
[Means for Solving the Problems]
The object of the present invention is to irradiate the conductive particle agglomerates in the medium with microwaves in the gigahertz region, and more preferably to apply dispersion treatment by applying at least one of ultrasonic irradiation and high-speed stirring processing thereafter. Achieved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention is applied to agglomerates of conductive particles, particularly conductive carbon black agglomerates that have a structure that is difficult to disperse, and exhibit an effective dispersion effect not found in other dispersion methods. Examples of 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. Apply to rubber and resin.
[0011]
In contrast, MT carbon black and FT carbon black, carbon black for ink, general carbon fiber, etc. used as fillers, reinforcing agents, etc. can of course be dispersed by the method of the present invention. Since a sufficiently good dispersion state can be formed even by stirring treatment or ultrasonic irradiation, the superiority of the method of the present invention is not particularly recognized.
[0012]
Examples of conductive particles other than carbon black include fine particles and fibers of metals such as copper, nickel, and silver.
[0013]
In the case of carbon-based particle agglomerates, it has a specific gravity of about 1.8 to 2.1. Therefore, when it is placed in a medium such as water, alcohol, hydrocarbon-based organic solvent, oligomer, etc., it precipitates at the bottom of the container containing the medium. , placing this in a field of microwave radiation of a closed container using a magnetron as an oscillator of the microwave, in the aggregate motion immediately as repelled in medium way, while moving around the vigorous vigorously irregular gradual Observe how it gets smaller. In addition, when water is added to copper powder having a particle size of about 2 to 10 μm and irradiated with microwaves , it is observed that the copper particles move and disperse violently as in the case of carbon black.
[0014]
The direction of repelling seems to be random, but is presumed to be due to the environment of the irradiation field. On the other hand, without the medium, when the carbon-based particle agglomerates are irradiated with microwaves , a spark is locally observed and a phenomenon in which the carbon-based particles are scattered is observed.
[0015]
In view of this, the dispersion process when the conductive particle agglomerates are irradiated with microwaves is due to the electromagnetic wave reflected from the surface of the conductive particle agglomerates causing the medium in the vicinity of the surface to rapidly overheat and It is considered that the instantaneous expansion force at the time of rapid gasification or the cutting of the agglomerated part due to rapid overheating has a mechanism for breaking the agglomerate into small pieces.
[0016]
A microwave having a frequency of gigahertz is used, and its irradiation density is about 0.01 to 5 Wh / g, preferably about 0.02 to 0.1 Wh / g, although it varies depending on the type and concentration of the dispersion medium.
[0017]
Instead of microwave irradiation, ultrasonic irradiation or or colloid mill, an effective distribution of just the carbon aggregate and high speed stirring using a homogenizer or the like is not achieved, after the irradiation of microwaves, these methods It is effective to apply in combination. Specifically, a method of irradiating with microwaves and then irradiating with ultrasonic waves, a method of performing high-speed stirring treatment, or a method of applying both methods in an arbitrary order is effective in further improving dispersibility. Alternatively, a method of irradiating microwaves after ultrasonic irradiation or high-speed stirring treatment in advance can be used.
[0018]
As the medium, water is preferably used from the viewpoint of non-pollution and non-flammability, but other than this, an organic solvent such as alcohol or toluene, an oligomer, or the like is used according to the purpose. In the case of an aqueous medium, in order to increase the affinity between the conductive particles and the conductive particles, a nonionic surfactant, an anionic surfactant, or a dispersant such as polyvinyl alcohol is added at about 0.1 to 5%, preferably Is used by adding about 1 to 3%.
[0019]
For example, when carbon-based agglomerates are dispersed in an aqueous medium, carbon-based agglomerates added at a ratio of about 1 to 20% by weight, preferably about 5 to 10% by weight, are initially precipitated at the bottom. When microwave irradiation is started, it moves vigorously as if it was vigorously stirred, and its mass becomes smaller as the irradiation amount increases, and finally forms an aqueous dispersion that does not precipitate even when irradiation is stopped. When about 10% by weight of ketjen black is added to the aqueous medium, the viscosity of the aqueous dispersion rapidly increases as the dispersion progresses, indicating thixotropy, that is, elasticity. become. At the same time, when the DC electrical resistance of the aqueous dispersion is measured, the DC electrical resistance also decreases rapidly in response to this sudden viscosity change.
[0020]
This is because the carbon-based agglomerates are loosened and dispersed in units of aggregates or small agglomerates in the aqueous medium, and they are in contact with each other in the medium, that is, the network structure of carbon black having elasticity and conductivity. It shows that it is in a formed state. This network is formed with water intervening, and its strength is extremely weak. Therefore, a syneresis phenomenon in which water gradually oozes when left standing.
[0021]
When the concentration of the aqueous dispersion is about 5% by weight or less, the state of the aqueous dispersion is exhibited while stirring. However, when the stirring is stopped, the carbon black dispersed is re-agglomerated, that is, the flocculation. Phenomenon occurs, and water and the carbon black network structure are separated.
[0022]
The carbon black thus dispersed is dispersed in a liquid and formed into a sheet shape by a paper-making method or the like, or by coprecipitation with a polytetrafluoroethylene dispersion or other polymer latex. After compounding, it is molded into a sheet or pipe, and as a highly conductive and flexible material, a conductive composite material, a catalyst carrier for gas phase reaction or liquid phase reaction, an electrode material for various batteries, etc. Used effectively.
[0023]
【The invention's effect】
By the method of the present invention, effective dispersion of agglomerates of conductive particles such as carbon black is achieved.
[0024]
【Example】
Next, the present invention will be described with reference to examples.
[0025]
Example 1
Place 200 ml of water and 5 g of acetylene black (specific gravity about 1.9) in a glass beaker with a capacity of 300 ml, and use an oven-type microwave generator (Toshiba ER-250) with a frequency of 2450 MHz (2.45 GHz) and an output of 0.5 KW microwave Was irradiated. When irradiation starts, the precipitated carbon begins to move around in water. The size of one carbon agglomerate broke into several pieces with its movement, and eventually the pieces became about 1-5 microns in size. The DC electric resistance of the dispersion 10 minutes after irradiation was 360Ω.
[0026]
Comparative Example 1
In Example 1, when a high-speed rotating homogenizer (MX type manufactured by Nippon Seiki Co., Ltd.) was used instead of the microwave generator and the stirring was performed at a high speed of 8000 rpm for 20 minutes, the DC electric resistance of the dispersion was 11000Ω.
[0027]
Comparative Example 2
In Example 1, instead of the microwave generator, an ultrasonic generator (Branson Sonifier450, horn: 3/4 inch cylindrical shape) is used, and the DC electric resistance of the dispersion after ultrasonic irradiation for 20 minutes is determined. It was 3100Ω when measured.
[0028]
Example 2
In Example 1, 2 g of ketjen black was used instead of acetylene black. The DC electric resistance of the dispersion after 10 minutes of microwave irradiation was 7000Ω.
[0029]
Comparative Example 3
In Example 2, when a high-speed rotation type homogenizer (MX type manufactured by Nippon Seiki Co., Ltd.) was used instead of the microwave generator and a high-speed stirring treatment was performed at a rotation speed of 8000 rpm for 20 minutes, the DC electric resistance of the dispersion was 10000Ω or more.
[0030]
Comparative Example 4
In Example 2, instead of the microwave generator, an ultrasonic generator (Branson Sonifier450, horn: 3/4 inch cylindrical shape) was used, and the DC electric resistance of the dispersion after ultrasonic irradiation for 20 minutes was determined. The measured value was 13000Ω.
[0031]
Example 3
In a glass beaker having a capacity of 300 ml, 200 ml of water, 0.2 g of a nonionic surfactant (Kao product Emulgen 210) and 2 g of acetylene black were placed and dispersed in the same manner as in Example 1 by irradiation with microwaves . The value of the DC electrical resistance of the dispersion with respect to the dispersion treatment time is shown by the curve (A) in the graph of FIG.
[0032]
Further, in the graph of FIG. 1, after such microwave irradiation, the case of high-speed stirring using the high-speed rotating homogenizer (B), and then the ultrasonic irradiation processing using the ultrasonic generator. In the case of (C), the relationship of the DC electric resistance value of the dispersion to the processing time is also shown.
[Brief description of the drawings]
1 is a graph showing the value of DC electric resistance of a dispersion with respect to dispersion treatment time in Example 3. FIG.

Claims (6)

A method for dispersing conductive particle agglomerates, comprising subjecting the conductive particle agglomerates in a medium to dispersion treatment by irradiating microwaves in a gigahertz region . The method for dispersing conductive particle agglomerates according to claim 1, wherein ultrasonic irradiation is performed after irradiating microwaves in the gigahertz region . The method for dispersing conductive particle agglomerates according to claim 1, wherein high-speed stirring is performed after irradiation with microwaves in the gigahertz region . The method for dispersing conductive particle agglomerates according to claim 1, wherein after irradiation with microwaves in the gigahertz region, ultrasonic irradiation and high-speed stirring are performed in an arbitrary order.   The method for dispersing conductive particle aggregates according to claim 1, wherein the dispersion treatment is performed in an aqueous medium in the presence of a surfactant or a dispersant. The method for dispersing conductive particle agglomerates according to claim 1 , wherein microwave irradiation in the gigahertz region is performed prior to ultrasonic irradiation or high-speed stirring treatment.

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