JPH07207289A - Production of polyaniline particle for electroviscous fluid - Google Patents

Abstract

PURPOSE:To produce polyaniline particles for a electroviscous fluid having a still higher density. CONSTITUTION:The production process of the polyaniline particles comprises the steps of reacting aniline with an oxidizing agent in an aqueous acid solution to form polyaniline particles, and reacting aniline with an oxidizing agent in an aqueous acid solution in the presence of the formed polyaniline particles.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing polyaniline particles for electrorheological fluids. More particularly, the present invention relates to a method of providing higher density, highly polarizable polyaniline particles.

[0002]

2. Description of the Related Art When a voltage is applied to a certain fluid, dispersed particles dispersed in the fluid are polarized, a bridge of particles is formed by an electrostatic force, and the apparent viscosity of the fluid is greatly changed. This phenomenon is called the Winslow effect, and a fluid exhibiting such a Winslow effect is an electrorheological fluid. Since the Winslow effect has a high response speed and gives a large change in viscosity with a small amount of electric power, the electrorheological fluid has been attempted to be applied to, for example, clutches, dampers, brakes, shock absorbers, suspensions and the like.

Conventional electrorheological fluids are those in which solid particles such as cellulose, starch, silica gel, ion exchange resin, lithium polyacrylate, etc. are dispersed as dispersion particles in silicone oil, kerosene, chlorinated paraffin, etc. as a dispersion medium. Are known.

These electrorheological fluids have problems such as low stress when a voltage is applied and poor stability, so that satisfactory results cannot be obtained.

In order to solve this problem, various dispersed particles have been studied. Japanese Patent Laid-Open No. 3-139598 discloses
An electrorheological fluid using polyaniline as dispersed particles is disclosed. The polyaniline obtained by oxidative polymerization is used as it is.

The electrorheological fluid using polyaniline as dispersed particles has greatly different fluid characteristics depending on the particle size and particle shape of the polyaniline. As a result of investigating the relation between the particle size of dispersed particles and the yield stress of the electrorheological fluid containing the particles, it was shown that the highest yield stress was obtained in the particles with a particle size of 45-100 μm. However, the polyaniline obtained by the oxidative polymerization shown in the above-mentioned reference is generally amorphous, and the number of particles having a particle size of 45 to 100 μm is about 1/3 of the whole. Also, because the particles are soft,
Even if it can be crushed, crushing is difficult, and it is difficult to control the particle size by this crushing. Further, as the electrorheological fluid, it is preferable that the base viscosity is low and the yield stress is high, and therefore the dispersed particles are preferably spherical or elliptical. The polyaniline obtained by the above-mentioned oxidative polymerization has an indefinite shape as described above, and it is difficult to obtain a preferable spherical shape even if it is pulverized. Further, it has been disclosed that suspension polymerization or emulsion polymerization is used as a method for obtaining dispersed particles of a spherical or elliptic polymer (Japanese Patent Laid-Open No. 3-30083).
192195). However, it is difficult to produce polyaniline by emulsion polymerization, and a sufficient degree of polymerization cannot be obtained even by suspension polymerization, making it difficult to apply these methods. Further, a method for polymerizing polyaniline by reacting aniline and ammonium persulfate in an aqueous acid solution at low temperature is disclosed (Japanese Patent Laid-Open No. 4-348192). In this method, the relationship between the polymerization conditions and the molecular weight, or the relationship between the polymerization conditions and the solubility is clear, but the shape and particle size of the obtained particles and the relationship between the polymerization conditions are not clear.

In order to solve these problems, the present inventor first conducted the reaction of aniline with an oxidizing agent in an acid aqueous solution having an acid concentration of 4 N or more with respect to the polymerization conditions of aniline and the shape and particle size of the obtained polyaniline particles. By doing so, polyaniline particles with a constant particle size can be obtained, and by reacting aniline with an oxidizing agent in an acid aqueous solution at a monomer concentration of 0.6 mol / l or less, polyaniline particles with high sphericity can be obtained. On the other hand, it was found that the sphericity can be further increased by reducing the average particle size by conducting the polymerization reaction in the presence of 25 to 75 g of polyvinyl alcohol (Japanese Patent Application No. 5-318174).

[0008]

According to the above method, polyaniline particles having a preferable particle size and sphericity can be obtained, but the particles contained many pores and the apparent density was low. Therefore, the polarization characteristics were not always sufficient for the volume of each particle.

The present invention is intended to solve the above-mentioned drawbacks of polyaniline particles used for electrorheological fluids and to provide a method for producing polyaniline particles having higher density and higher polarization characteristics.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above problems of polyaniline particles used in electrorheological fluids, the present inventors have found that after polymerizing aniline,
It was found that by polymerizing aniline again in the presence of the obtained polyaniline, polyaniline is synthesized in the pores of the first polymerized polyaniline, which fills the pores to obtain polyaniline particles with high density. The present invention has been completed.

That is, the method for producing polyaniline of the present invention comprises a step of reacting aniline and an oxidizing agent in an aqueous acid solution to form polyaniline particles, and then, in the presence of the polyaniline particles, the aniline and the oxidizing agent are in an aqueous acid solution. It is characterized by comprising a step of reacting inside.

In the specific production method of the present invention, the oxidizing agent used for the polymerization of aniline is not particularly limited, and those generally used in radical polymerization may be used, and examples thereof include peroxodisulfate and lauroyl peroxide. Etc. are illustrated. The aqueous acid solution is not particularly limited, but hydrochloric acid, sulfuric acid, perchloric acid and the like are preferable.

The first polymerization of aniline is carried out by general oxidative polymerization. At this time, it is preferable to obtain polyaniline having an appropriate particle size distribution and a shape close to a true sphere. Therefore, it is preferable to carry out the polymerization using the method described in Japanese Patent Application No. 5-318174. That is, it is preferable to polymerize aniline in an aqueous acid solution having a monomer concentration of 0.6 mol / l or less and an acid concentration of 4 N or more in the presence of polyvinyl alcohol (more preferably 25 to 75 g of polyvinyl alcohol per 1 mol of aniline). .

The polyaniline thus obtained has an appropriate particle size distribution and a shape close to a true sphere. If desired, this is separated by sieving to obtain particles having a more preferable particle size. If you do not adjust the acid solution concentration,
Although those having a wide particle size distribution can be obtained, in this case as well, those having an appropriate particle size may be separated by sieving after polyaniline polymerization.

The first polymerized polyaniline particles are
It has a specific surface area of 15 to 20 m ² / g and contains many pores. Therefore, by polymerizing aniline again in the pores, the pores are filled and the density becomes higher. That is, aniline is similarly oxidatively polymerized in an aqueous acid solution in the presence of the first polymerized polyaniline. The oxidizing agent and the aqueous acid solution are the same as those used for the first polymerization. By the second polymerization, not all the pores of the polyaniline polymerized first are filled, but the sealed particles and the unsealed particles may be mixed. Since the sealed particles have a higher specific gravity than the unsealed particles, both of them can be easily separated by centrifugation. Therefore, if only the sealed particles are separated by centrifugation,
Higher characteristics can be obtained.

The second polymerization of polyaniline also proceeds outside the pores of the first polymerized polyaniline, but in this case also, the separation is easy due to the difference in specific gravity. For example, a solvent having an appropriate specific gravity can be mixed with polyaniline particles, and the difference in specific gravity can be used by centrifugation to separate the particles even if the particle diameters are the same. Furthermore, by utilizing the fact that the concentration of the aqueous acid solution at the time of polymerization influences the particle size of the obtained polyaniline, the first polymerization is carried out in an aqueous acid solution of 4 N or more, and the second polymerization is performed at a lower level, for example, 1 to Since the polyaniline formed by the second polymerization is smaller in particle size than the first polymerized polyaniline by carrying out in a 3N aqueous acid solution, sifting is facilitated by utilizing this difference in diameter.

Thus, by polymerizing aniline in the pores of the first polymerized polyaniline, the polyaniline particles filling the pores and having a specific surface area of about 4 to 8 m ² / g and having a higher apparent density are obtained. can get.

An electrorheological fluid can be obtained by dispersing the polyaniline particles thus obtained in an insulating dispersion medium. The insulating dispersion medium is not particularly limited, and examples thereof include hydrocarbon oils, ester oils, aromatic oils and silicone oils, which may be used alone or in combination of two or more.

The proportion of the polyaniline dispersed particles and the dispersion medium is preferably such that the content rate of the dispersed particles is 5 to 30%. If it is less than 5%, the electrorheological effect is low, and if it exceeds 30%, the basal viscosity becomes high.

To the electrorheological fluid composition, conventionally used additives such as surfactants, dispersants and thickeners may be added.

[0021]

The polyaniline obtained by the conventional method does not always have sufficient characteristics because it contains many pores in its particles. According to the method of the present invention, polyaniline is first polymerized, and then polyaniline is polymerized in the presence of the polyaniline, thereby filling the pores thereof with polyaniline, resulting in a decrease in specific surface area and an increase in apparent density. By using particles, a higher performance electrorheological fluid can be obtained.

[0022]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention.

Example 1 150 ml of 4N sulfuric acid was added to a 500 ml flask, and 10 ml (0.10 mol) of aniline and 5 g of polyvinyl alcohol were dissolved therein. Next, ammonium peroxodisulfate was dissolved in 4N sulfuric acid in an equimolar amount (0.10 mol) with aniline, followed by cooling with ice. The aniline solution was stirred while being kept at -5 to -3 ° C, and the ammonium peroxodisulfate solution was slowly added dropwise thereto. After completion of the dropping, the particles were filtered and washed to obtain polyaniline particles. This polyaniline particle has 16.2 m ² / g
It had a specific surface area of.

The polyaniline particles thus obtained were separated by sieving to obtain particles of 45 to 100 μm. This particle size 45
10 g of .about.100 .mu.m polyaniline particles were dipped in 10 ml of aniline and left overnight. The mixture of the polyaniline particles and aniline was put in a 2 liter separable flask, and 500 ml of 1N sulfuric acid aqueous solution was added thereto. Then, to this mixture was slowly added a solution of 25 g of ammonium peroxodisulfate dissolved in an aqueous solution of sulfuric acid having the same concentration while stirring. And it was made to react in -5 to -3 degreeC, stirring. Then, polyaniline particles were obtained by filtering and drying. Among the particles obtained, those having a particle size of 45 to 100 μm had a specific surface area of 5.2 m ² / g, and polyaniline particles in which pores were filled and which had a high apparent density were obtained.

The polyaniline particles (densified product)
80 cc of silicone oil was added to 22 g to prepare an electrorheological fluid. The yield stress characteristics of this fluid were measured and the results are shown in FIG. An electrorheological fluid was similarly prepared using the first polymerized polyaniline particles having a specific surface area of 16.2 m ² / g (untreated product), and the yield stress characteristic measurement results are also shown in FIG. 1. It can be seen that the use of the polyaniline produced by the method of the present invention improves the yield stress characteristics of the electrorheological fluid using the particles.

Further, in addition to the densified product and the untreated product, an electrorheological fluid was prepared using a 1: 1 mixture of the two as polyaniline particles, and the yield stress characteristics were measured. The result is shown in FIG. From FIG. 2, it can be seen that the yield stress is improved more than the untreated product even in the mixed state of the treated product and the untreated product.

[0027]

EFFECTS OF THE INVENTION According to the present invention, the pores of the dispersed polyaniline particles are filled to obtain higher density polyaniline particles, and an electrorheological fluid having higher characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing improvement in characteristics of an electrorheological fluid using polyaniline particles obtained by the method of the present invention.

FIG. 2 is a graph showing improvement in characteristics of an electrorheological fluid using polyaniline particles obtained by the method of the present invention.

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Claims (2)

[Claims] 1. A method comprising the steps of reacting aniline and an oxidizing agent in an aqueous acid solution to form polyaniline particles, and then reacting the aniline and the oxidizing agent in an aqueous acid solution in the presence of the polyaniline particles. A method for producing polyaniline particles for an electrorheological fluid. 2. A step of reacting aniline and an oxidizing agent in an acid aqueous solution having an acid concentration of 4 N or more to form polyaniline particles, and then, in the presence of the polyaniline particles, the aniline and the oxidizing agent are added in an acid concentration of 1 to 3. A method for producing polyaniline particles for an electrorheological fluid, comprising the step of reacting in a prescribed aqueous acid solution.