JP2005314538A - Conductive fine particle and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive fine particle having small particle diameter and high dispersion stability in an organic solvent. <P>SOLUTION: The conductive fine particle is composed of pyrrole and/or a pyrrole derivative, having a particle diameter of 1-30 nm and containing an anionic surfactant. The conductive fine particle is produced e.g. by adding pyrrole and/or pyrrole derivative monomer to an O/W-type emulsion obtained by mixing and stirring an organic solvent, water and an anionic surfactant and carrying out the oxidative polymerization of the monomer. A conductive coating is produced by dispersing the conductive fine particle in an organic solvent. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to conductive fine particles and a method for producing the same. Specifically, the present invention relates to conductive fine particles having a fine particle size and good dispersion stability in an organic solvent.

  Conductive polymers represented by polypyrrole, polythiophene, and polyaniline are relatively stable in air and easy to synthesize, so conductive paints, anticorrosive paints, semiconductor materials, capacitor electrolytes, organic EL It is widely used industrially for applications such as element hole transport materials and secondary battery electrode materials. In particular, polypyrrole is attracting attention as an electrolytic capacitor, polythiophene as a polymer organic EL device, and polyaniline as a secondary battery. However, since these conductive polymers are generally insoluble and cannot be melted by heating, the molding process is very difficult.

Therefore, as a means for solving the problems related to the processability of the conductive polymer, for example, an equimolar anionic surfactant and aniline are reacted in a solvent to form an aniline-surfactant salt. A method for producing polyaniline soluble in water and / or an organic solvent, characterized by adding an oxidizing agent while suppressing an increase in heat and performing oxidative polymerization (see, for example, Patent Document 1). In this method, by combining aniline and an equimolar surfactant, the resulting polyaniline becomes soluble in various solvents, particularly water, and a conductive thin film can be easily formed by applying a polyaniline solution.
Japanese Patent No. 3426637

And a composite of at least one kind of inorganic fine particles selected from the group consisting of metal, carbon, inorganic oxide, inorganic phosphate, and inorganic phosphite, and an organic polymer having a π-conjugated double bond. The characteristic conductive polymer composite fine particles are also known (see, for example, Patent Document 2). Here, as the organic polymer, aniline, pyrrole, thiophene and substituted products thereof can be used, and the conductive polymer composite fine particles thus obtained have not only good workability but also heat resistance. It also has the functions inherent to inorganic fine particles such as water resistance, adhesion to metal, conductivity, redox property, ultraviolet / visible light blocking property, hiding property, hardness, and magnetism.
Japanese Patent Application Laid-Open No. 11-241021

Further, a pyrrole is polymerized in the presence of at least one surfactant selected from polyvinyl alcohol or polyvinyl alcohol and a nonionic surfactant or an anionic surfactant. A manufacturing method is also known (for example, refer to Patent Document 3). According to this method, it is possible to produce a uniform and stable polypyrrole aqueous dispersion, which can be mixed with an aqueous polymer solution such as an emulsion or latex to produce a molded article having a complex shape having arbitrary conductivity. It becomes possible.
Japanese Patent Publication No. 7-78116

By the way, polyaniline requires a protonic acid to develop conductivity, but there is a problem that dedoping occurs due to a change with time due to temperature and humidity, and the acid is liberated and causes corrosion. For example, a conductive paint obtained by dissolving polyaniline prepared in accordance with the disclosure of Japanese Patent No. 3426637 is coated on a 5 cm × 5 cm polyethylene terephthalate film, and a 3 cm × 3 cm pure copper test piece is sandwiched between the films, 70 24 under the environment of ℃ and humidity 95%
Corrosion was observed on the specimen when left for a period of time. From this result, it is clear that polyaniline cannot be used in applications that come into contact with materials that are subject to decomposition by acids such as metals. Furthermore, since the polyaniline has protons involved in the expression of conductivity, there is also a problem that the conductivity varies with humidity.

Similarly, the polypyrrole described in Japanese Patent Application Laid-Open Nos. 11-241021 and 7-78116 also has humidity dependency due to the influence of hydrophilic groups. Furthermore, it was insufficient in terms of conductivity and long-term dispersion stability.
Further, they were stably dispersed in an aqueous solution, but could not be dispersed in an organic solvent and aggregated. Accordingly, it has been impossible to obtain a solvent-based conductive coating material that is superior in wettability, quick-drying property, and coating film strength after coating film formation as compared with water-based coating material.

  The present invention solves the above-described problems, and an object thereof is to provide conductive fine particles having excellent dispersion stability in an organic solvent. Furthermore, an object of the present invention is to provide a reliable method for producing such conductive fine particles and a product for use having excellent performance using the fine particles, particularly a solvent-based conductive coating.

  As a result of diligent research, the present inventor has found that conductive fine particles having good dispersion stability with respect to an organic solvent can be obtained.

  In particular, a monomer of pyrrole and / or a pyrrole derivative is added to an O / W emulsion obtained by mixing and stirring an organic solvent, water, and an anionic surfactant, and the monomer is oxidatively polymerized. Thus, it has been found that the conductive fine particles of the present invention can be easily produced.

Therefore, the present invention
Conductive fine particles comprising pyrrole and / or a pyrrole derivative and having a particle diameter of 1 to 30 nm, containing conductive anionic surfactant, an organic solvent, water, and anionic surfactant The present invention relates to the method for producing conductive fine particles, wherein a monomer of pyrrole and / or a pyrrole derivative is added to an O / W type emulsion obtained by mixing and stirring an agent, and the monomer is oxidatively polymerized.

  According to the present invention, it is possible to obtain conductive fine particles having an anionic surfactant and having a particle size of 1 to 30 nm and having dispersion stability in an organic solvent. Moreover, these are fine powders in a dry state, and can be imparted with conductivity by being added to a resin or the like.

  The conductive fine particles obtained in the present invention are fine particles mainly composed of pyrrole and / or a pyrrole derivative and containing an anionic surfactant. And the characteristic is that it can disperse | distribute in a fine particle size and an organic solvent.

  The particle diameter of the conductive fine particles of the present invention is specifically 1 to 30 nm. This particle size is much smaller than the particle size of several hundred nm that the conventional conductive fine particles have. Further, the conductive fine particles of the present invention have a narrow particle size distribution very close to monodispersion that 90% or more of the total fine particles are included in the range of ± 5 nm of the average particle size. This is different from conventional conductive fine particles having a wide diameter distribution. This very small particle size is considered to be one of the factors of long-term dispersion stability of the conductive fine particles of the present invention. Further, since the particle size is small, it is considered that the coating film has transparency when it is made a conductive paint.

The conductive fine particles of the present invention can be obtained, for example, by oxidative polymerization of pyrrole and / or a pyrrole derivative monomer in an O / W emulsion.
The conductive fine particles of the present invention obtained by polymerization in an O / W type emulsion are expected to have a structure as illustrated in the schematic diagram of FIG. First, an O / W emulsion is formed using water, an organic solvent, and an anionic surfactant. Here, since the anionic surfactant forms micelles around an organic phase composed of an organic solvent, a hydrophilic group of the anionic surfactant appears on the surface side of the micelle.
When a pyrrole monomer is added to the emulsion, the pyrrole monomer is dissolved in the aqueous phase, and a polypyrrole is formed by adding an oxidizing agent. As the polymerization of polypyrrole proceeds, it is presumed that polypyrrole becomes difficult to dissolve in the aqueous phase and that the chain length of polypyrrole is extended with the hydrophilic group of the anionic surfactant as a nucleus.

As a result, in the polypyrrole, the anionic surfactant covers the entire O / W emulsion, the anionic surfactant is taken into the polypyrrole particles, and the hydrophilic group of the anionic surfactant functions as a dopant. Guessed.
Therefore, when the anionic surfactant is used only for the formation of the O / W emulsion, the hydrophilic group of the anionic surfactant is not exposed on the surface of the polypyrrole particle, and the polypyrrole particle is Even after the coating film is formed, it is considered that the conductivity is not expressed by ions. This means that if the addition amount of the anionic surfactant is within a specific range, the humidity dependence of the conductive coating film appears as the addition amount increases, whereas the humidity dependence of the conductive coating film does not appear. This is consistent with the result of coming.

Moreover, when there is much addition amount of an anionic surfactant, it is thought that the free anionic surfactant exists in a coating material.
Unlike the conductive fine particles produced using inorganic fine particles as the core, the conductive fine particles of the present invention have an anionic surfactant that is an organic compound as a core, which is advantageous in terms of dispersibility in a synthetic resin. It appears to be.

  In the production of the conductive fine particles of the present invention, when the oxidative polymerization reaction is stopped, the reaction system is divided into two phases, an organic phase and an aqueous phase. At this time, unreacted monomers, oxidizing agents and salts are in the aqueous phase. Dissolves in and remains. When the organic phase is separated and recovered and washed several times with ion exchange water, polypyrrole fine particles dispersed in an organic solvent can be obtained.

  Examples of pyrrole and derivatives thereof that can be used in the production include pyrrole, N-methylpyrrole, N-ethylpyrrole, N-phenylpyrrole, N-naphthylpyrrole, N-methyl-3-methylpyrrole, and N-methyl-3-pyrrole. Ethyl pyrrole, N-phenyl-3-methyl pyrrole, N-phenyl-3-ethyl pyrrole, 3-methyl pyrrole, 3-ethyl pyrrole, 3-n-butyl pyrrole, 3-methoxy pyrrole, 3-ethoxy pyrrole, 3- n-propoxypyrrole, 3-n-butoxypyrrole, 3-phenylpyrrole, 3-toluylpyrrole, 3-naphthylpyrrole, 3-phenoxypyrrole, 3-methylphenoxypyrrole, 3-aminopyrrole, 3-dimethylaminopyrrole, 3 -Diethylaminopyrrole, 3-diphenylaminopyrrole 3-methylphenylamino pyrrole, 3-phenyl naphthyl amino pyrrole, and the like. Particularly preferred is pyrrole.

Various anionic surfactants used in the production can be used, but those having a plurality of hydrophobic ends (for example, those having a branched structure in a hydrophobic group or those having a plurality of hydrophobic groups) are preferred. . By using such an anionic surfactant having a plurality of hydrophobic ends, stable micelles can be formed.
Among anionic surfactants having multiple hydrophobic ends, di-2-ethylhexyl sodium sulfosuccinate (4 hydrophobic ends), di-2-ethyloctyl sodium sulfosuccinate (4 hydrophobic ends) and branched type Alkyl benzene sulfonates (two hydrophobic ends) can be suitably used.

  The amount of the anionic surfactant in the reaction system is preferably less than 0.2 mol, more preferably 0.05 mol to 0.15 mol, relative to 1 mol of the monomer of pyrrole and / or a pyrrole derivative. If the amount is less than 0.05 mol, the yield and the dispersion stability are lowered. On the other hand, if the amount is 0.2 mol or more, the conductive fine particles obtained may have a humidity dependency on the conductivity.

  In the production, the organic solvent forming the organic phase of the emulsion is preferably hydrophobic. Of these, toluene and xylene, which are aromatic organic solvents, are preferable from the viewpoint of the stability of the O / W emulsion and the affinity with the pyrrole monomer. Although the polypyrrole can be polymerized with an amphoteric solvent, it becomes difficult to separate the organic phase and the aqueous phase when the produced conductive fine particles are recovered.

  The ratio of the organic phase to the aqueous phase in the emulsion is preferably 75% by volume or more in the aqueous phase. When the water phase is 20% by volume or less, the amount of pyrrole monomer dissolved is reduced and the production efficiency is deteriorated.

  Examples of the oxidizing agent used in the production include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid and chlorosulfonic acid, organic acids such as alkylbenzenesulfonic acid and alkylnaphthalenesulfonic acid, potassium persulfate, ammonium persulfate and peroxidation. Peroxides such as hydrogen can be used. These may be used alone or in combination of two or more. Polypyrrole can be polymerized even with a Lewis acid such as ferric chloride, but the produced particles may aggregate and the polypyrrole may not be finely dispersed. Particularly preferred oxidizing agents are persulfates such as ammonium persulfate.

  The amount of the oxidizing agent in the reaction system is preferably 0.1 mol or more and 0.8 mol or less, more preferably 0.2 to 0.6 mol with respect to 1 mol of the monomer of pyrrole and / or pyrrole derivative. . If the amount is less than 0.1 mol, the degree of polymerization of the monomer decreases, making it difficult to separate and collect the conductive fine particles. On the other hand, if the amount is 0.8 mol or more, the polypyrrole aggregates to increase the particle size of the conductive fine particles. Stability and transparency of the coating deteriorate.

The method for producing the conductive fine particles is performed, for example, in the following steps:
(A) a step of preparing an emulsion by mixing and stirring an anionic surfactant, an organic solvent and water;
(B) a step of dispersing a monomer of pyrrole and / or a pyrrole derivative in an emulsion, (c) a step of oxidative polymerization of the monomer to cause polyanol to contact and adsorb on an anionic surfactant,
(D) A step of separating the organic phase and collecting the conductive fine particles.

  Each of the above steps can be performed using means known to those skilled in the art. For example, the mixing and stirring performed at the time of preparing the emulsion is not particularly limited. For example, a magnetic stirrer, a stirrer, a homogenizer, or the like can be selected as appropriate. The polymerization temperature is 0 to 25 ° C, preferably 20 ° C or less. If the polymerization temperature exceeds 25 ° C., side reactions occur, which is not preferable.

In the conductive fine particles of the present invention thus obtained, conductive fine particles having high dispersion stability in an organic solvent can be preferably used as the conductive component of the conductive paint. The conductive paint is obtained by dispersing the conductive fine particles of the present invention in an organic solvent, and a resin such as a dispersion stabilizer, a thickener, and an ink binder may be added as required for the purpose of use and application. Is possible.
In addition, these conductive fine particles can be dried to form powdered conductive fine particles, and the powdered conductive fine particles can also be used as a conductive filler or the like in a synthetic resin molded product or the like.

Moreover, a conductive thin film can be obtained by applying the conductive paint of the present invention to a substrate and drying it. The object to be applied is not particularly limited, but it is necessary to select it so as not to be damaged by the organic solvent contained in the conductive paint. Also, the coating method is not particularly limited, and printing or coating can be performed using, for example, a gravure printing machine, an inkjet printing machine, dipping, a spin coater, a roll coater, or the like. The conductive thin film thus obtained exhibits a resistance value of 10 ¹² Ω or less, more particularly 10 ⁹ Ω or less.

  In addition to the conductive paint, the conductive fine particles of the present invention are preferably applied to various applications such as a rust preventive paint, a semiconductor material, a capacitor electrolyte, a hole transport material for an organic EL element, and an electrode material for a secondary battery. can do.

  The following examples illustrate the invention in more detail. However, the examples are for illustrating the present invention and are not intended to limit the present invention in any way.

Example 1
1.5 mmol of di-2-ethylhexyl sodium sulfosuccinate was dissolved in 50 mL of toluene, and further 100 mL of ion-exchanged water was added and stirred until emulsification was maintained at 20 ° C. To the obtained emulsion, 21.2 mmol of pyrrole monomer was added and stirred for 30 minutes, and then 50 mL (corresponding to 0.4 mol) of a 0.2 M aqueous ammonium persulfate solution was added dropwise little by little to react for 4 hours. After completion of the reaction, the organic phase was recovered, washed several times with ion exchange water, and black conductive fine particles were obtained in a state dispersed in toluene.

FIG. 2 is an electron micrograph of conductive fine particles of Example 1.
As is apparent from FIG. 2, the conductive fine particles of Example 1 have a very uniform particle size.

FIG. 3 is a graph illustrating the particle size distribution of the conductive fine particles produced according to the method described in Example 1 of the present application and in Japanese Patent Application Laid-Open Nos. 11-241021 and 7-78116.
As is apparent from FIG. 3, the conductive fine particles of the present invention have a much finer particle size than those of the prior art. Furthermore, the particle size distribution is close to monodisperse. Such a fine particle size and a narrow particle size distribution are considered to be one factor that the conductive fine particles of the present invention show good results in dispersion stability.
In addition, this particle size distribution is the result measured by the laser Doppler method using Microtrac Nanotrac UPA150.
The conductive fine particles obtained by the method of Example 1 of the present invention had an average particle size of 2.5 nm, and 99% was contained within a range of ± 0.8 nm.

Examples 2-7 and Comparative Examples 1-2
According to the method described in Example 1, the type and amount of an anionic surfactant and the type and amount of an oxidizing agent were changed as shown in Table 1 to produce conductive fine particles.
Further, Comparative Example 1 was prepared without using a surfactant, and Comparative Example 2 was prepared using aniline instead of pyrrole.

Next, the conductive fine particles obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were made into a conductive paint using the same method, and the properties of the conductive thin film obtained by applying the conductive paint to a glass plate Was evaluated. The evaluation was based on the following criteria for the resistance value (Ω) of the conductive coating, the dispersion stability of the conductive coating, the transparency of the conductive coating, and the humidity dependence of the resistance value of the conductive coating. .
Dispersion stability (solvent: toluene)
○: stably dispersed for more than 1 month Δ: aggregation occurs and precipitates in 1 week ×: aggregation immediately after dispersion Transparency ○: transparent by visual observation Δ: black dots are visible in the coating film ▲ : The coating film appears cloudy ×: Only a thick coating film can be formed, and the coating film is opaque Humidity dependency ○: The difference in resistance value between the case of 30% humidity and 70% humidity is one digit or less ×: The difference in resistance between the case of 30% humidity and the case of 70% humidity is one digit or more. The results are shown in Table 1 below. Moreover, the numerical value shown about pyrrole, surfactant, and oxidizing agent in Table 1 shows the addition amount (mmol) per 50 mL of organic solvents.

In Examples and Comparative Examples, it was confirmed by FT-IR (KBr method) that the conductive fine particles contained a surfactant.
The chart of FT-IR in Example 1, the chart of FT-IR of polypyrrole, and the chart of FT-IR of surfactant sodium di-2-ethylhexyl sulfosuccinate are shown in FIG. 4, FIG. 5, and FIG. 6, respectively.

界面活性剤１：スルホコハク酸ジ−２−エチルヘキシルナトリウム（疎水性末端４つ）
界面活性剤２：ペンタデシルベンゼンスルホン酸ナトリウム（疎水性末端２つ）
酸化剤：過硫酸アンモニウム

Surfactant 1: Sodium di-2-ethylhexyl sulfosuccinate (4 hydrophobic ends)
Surfactant 2: Sodium pentadecylbenzenesulfonate (two hydrophobic ends)
Oxidizing agent: ammonium persulfate

The conductive fine particles of the present invention shown in Examples 1 to 3 and 6 have good dispersion stability in an organic solvent, and can be sufficiently used as a conductive coating material. The conductive fine particles can be used as an organic solvent. When the dispersed material was applied to a substrate, the transparency and the humidity dependency of the resistance value were also good and very favorable.
The conductive fine particles of the present invention shown in Examples 4, 5 and 7 were slightly inferior in dispersion stability to organic solvents than Examples 1 to 3, but were used with proper stirring before use. if,
It can be used satisfactorily as a conductive paint.
In Comparative Example 1, fine particles cannot be formed, and in Comparative Example 2, the humidity dependency is large.

FIG. 7 shows the conductive fine particles of Examples 1 and 6 of the present application, and the conductive fine particles produced according to the methods described in Japanese Patent No. 3426637, Japanese Patent Laid-Open No. 11-244101, and Japanese Patent Publication No. 7-78116. In the graph which shows the relation between the resistance value of the thin film and the humidity of the environment to which the thin film is exposed when the conductive paint is manufactured from the conductive fine particles and the conductive thin film is formed by applying the conductive paint. is there.
As is apparent from FIG. 7, according to the present invention, the conductive thin film showed no humidity dependence on its conductivity, and the graph was substantially parallel to the X axis.
On the other hand, the conductive thin film obtained according to the comparative example and the prior art has humidity dependency on the conductivity, and the resistance value suddenly drops as the humidity increases.

FIG. 1 is a schematic diagram illustrating the expected structure of the conductive fine particles of the present invention. FIG. 2 is a view showing an electron micrograph of the conductive fine particles produced in Example 1. FIG. 3 is a graph illustrating the particle size distribution of the conductive fine particles of the present invention and the prior art. 4 is an FT-IR chart of the conductive fine particles obtained in Example 1. FIG. FIG. 5 is an FT-IR chart of polypyrrole. FIG. 6 is an FT-IR chart of surfactant sodium di-2-ethylhexyl sulfosuccinate. FIG. 7 is a graph illustrating the correlation between the resistance value and humidity of a conductive thin film formed from conductive fine particles of the present invention and the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electroconductive fine particle 2 Anionic surfactant 21 Hydrophilic part 22 Hydrophobic part 3 Polypyrrole 4 Water phase 5 Organic phase

Claims (6)

Conductive fine particles made of pyrrole and / or a pyrrole derivative and having a particle diameter of 1 to 30 nm and containing an anionic surfactant. The conductive fine particles according to claim 1, wherein the anionic surfactant is a molecule having a plurality of hydrophobic ends. A pyrrole and / or pyrrole derivative monomer is added to an O / W type emulsion obtained by mixing and stirring an organic solvent, water, and an anionic surfactant, and the monomer is oxidatively polymerized. The method for producing conductive fine particles according to claim 1 or 2. The method according to claim 3, wherein the amount of the anionic surfactant is 0.05 to 0.15 mol with respect to 1 mol of the monomer. The production method according to claim 3, wherein the amount of the oxidizing agent used for the oxidative polymerization is 0.2 to 0.6 mol with respect to 1 mol of the monomer. A conductive paint comprising the conductive fine particles according to claim 1 dispersed in an organic solvent.

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