JP3106577B2 - Manufacturing method of magnetic fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a magnetic fluid. More specifically, the present invention relates to a method for producing a magnetic fluid in which ferrite fine particles are stably dispersed at a high concentration in a low-vapor-pressure base oil to thereby improve saturation magnetization.

[0002]

2. Description of the Related Art Ferrite fine particles are produced by a pulverization method, a coprecipitation method, a vapor deposition method, etc. Among these methods, a coprecipitation method is generally used in view of purity, particle size control, productivity, and the like. Is used. By the way, since the coprecipitation method is a precipitation reaction from an aqueous solution containing iron ions, the generated magnetic fine particles are obtained in a state of an aqueous suspension suspended in the aqueous solution.

On the other hand, it is desirable that the magnetic fine particles for a magnetic fluid be dispersed one by one without being aggregated. Therefore, in the case of the coprecipitation method magnetic fine particles, without going through a drying step including a risk of sticking and aggregation of fine particles,
It is necessary to adsorb a surfactant for preventing sticking and coagulation on the surface of the fine particles in the state of a dispersion, and accordingly, a water-soluble surfactant is used.

[0004] In the magnetic fluid in which the magnetic fine particles on which the water-soluble surfactant is adsorbed are dispersed, the dispersed base oil is limited to a relatively volatile solvent such as kerosene and toluene. When a magnetic fluid is used for sealing a magnetic fluid, polishing a magnetic fluid, or the like, evaporation of the base oil is regarded as an important problem that impairs the function itself of the magnetic fluid.

[0005] The magnetic fluid is generally obtained by dispersing ferrite fine particles in a base oil using a dispersant such as a higher fatty acid salt or sorbitan ester. However, simply dispersing ferrite fine particles in a base oil having a low vapor pressure does not provide high dispersibility, and is not very practical.

[0006] In such a dispersion in a low vapor pressure base oil, even if excellent dispersibility is obtained, the low vapor pressure base oil exhibits a kinematic viscosity (40 ° C) of less than 1 Cst of a general organic solvent or water. However, since it has a high kinematic viscosity of about 8 to 50 Cst (40 ° C.), it takes a very long time to form a uniform suspension. In addition, not all ferrite fine particles to be dispersed form a stable suspension, but a considerable proportion of ferrite fine particles are removed during purification such as centrifugation, resulting in a problem that the efficiency is very poor.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently produce a magnetic fluid in which ferrite fine particles are stably dispersed in a low vapor pressure base oil at a high concentration.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
To the aqueous suspension of ferrite fine particles, a hydrocarbon solution of N-polyalkylene polyamine-substituted alkenyl succinimide is added, and the hydrocarbon solvent is miscible and the N-polyalkylene polyamine-substituted alkenyl succinimide is hardly soluble or After the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed to the ferrite fine particles while gradually adding the insoluble organic solvent,
The organic solvent, water and the hydrocarbon solvent are distilled off, and the residue
N-polyalkylene polyamine-substituted alkenyl succinimide-adsorbed ferrite fine particles, 0.1mmHg at 25 ℃
This is achieved by producing a magnetic fluid by dispersing in a low vapor pressure base oil having the following vapor pressure:

As the ferrite fine particles, those produced by a coprecipitation method, which is advantageous in terms of purity, particle size control and, above all, productivity, are used in the form of an aqueous suspension as it is. That is, the formation of the aqueous suspension by the coprecipitation method is performed through a series of steps of dropping of an aqueous NaOH solution to the aqueous solution of the iron salt mixture, aging, cooling and decanting of the salt, where the particle size is about 50 to 50. 30
0 °, preferably about 70-120 ° ferrites for about 0.1-5
A suspension dispersed at a concentration of 0% by weight, preferably about 1 to 30% by weight, is obtained.

As the N-polyalkylene polyamine-substituted alkenyl succinimide, the following are used. (Hereinafter the margin) R: a hydrocarbon group having 12 to 24 carbon atoms, a polybutenyl group having a molecular weight of about 300 to 2000, R ': an alkylene group having 1 to 6 carbon atoms, which can be the same or different when two or more R's are repeated n: 1 to 5 m: 0 to 4

N-polyalkylenepolyamine-substituted alkenyl succinimides are prepared by converting them into aliphatic, alicyclic or aromatic hydrocarbon solvents having a boiling point of about 60 to 200 ° C., such as n-hexane, n-heptane, n-octane, It is used as a solution in which isooctane, n-decane, cyclohexane, toluene, xylene, mesitylene, petroleum ether, petroleum benzine, ligroin, naphtha and the like are dissolved at a concentration of about 0.01 to 0.5 mol, preferably about 0.1 to 0.5 mol.

These hydrocarbon solutions are generally used in a volume ratio of about 0.01 to 100, preferably about 1 to 100 with respect to the aqueous suspension. The mixing of the two is performed using a homogenizer or the like under stirring conditions such that an emulsion is formed. By stirring under such stirring conditions, the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed on the ferrite fine particles at the interface of the emulsion. It is desirable to carry out a stirring treatment under a temperature condition of about 30 ° C., and such treatment is carried out for about 30 to 60
Done for minutes.

At this time, as the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed on the ferrite fine particles, the concentration of the N-polyalkylene polyamine-substituted alkenyl succinimide in the hydrocarbon solution decreases. As a result, the orientation density at the emulsion interface decreases. Therefore, a sparingly soluble or insoluble organic compound which is miscible with the hydrocarbon used as the solvent for the N-polyalkylenepolyamine-substituted alkenyl succinimide and has a solubility of about 1 mmol or less for the N-polyalkylene polyamine-substituted alkenyl succinimide. Solvent is added during the adsorption.

Examples of the organic solvent include alcohols such as methanol, ethanol and isopropanol, and ketones such as acetone and methyl ethyl ketone. By the time the stirring treatment at the time of adsorption is completed, these organic solvents have a volume ratio of about 0.5 to 1 with respect to the hydrocarbon which is the solvent of the N-polyalkylene polyamine-substituted alkenyl succinimide. Are added gradually at a constant addition rate. As a result, the orientation density of the N-polyalkylene polyamine-substituted alkenyl succinimide at the emulsion interface is maintained, and it is efficiently adsorbed on the ferrite fine particles.

Thereafter, water and the hydrocarbon solvent are distilled off, and the residue is dissolved in toluene-acetone, toluene-methanol,
Washing is performed with a mixed solvent such as n-hexane-acetone and isooctane-acetone, generally with an equal amount of a mixed solvent. By such washing, excess N-polyalkylenepolyamine-substituted alkenyl succinimide which increases the viscosity when prepared into a magnetic fluid or lowers the dispersion concentration of ferrite fine particles is removed. After washing, the ferrite fine particles are dried if necessary.

The ferrite fine particles coated with the N-polyalkylenepolyamine-substituted alkenyl succinimide thus obtained are dispersed by adding a low-vapor-pressure base oil thereto. The dispersibility in pressurized base oil is in a good state.

As a low vapor pressure base oil, 0.1 m at 25 ° C.
Liquid having a vapor pressure of mHg or less, preferably 0.01 mmHg or less, such as natural oils such as white oil (liquid paraffin), mineral oil, spindle oil and the like, or synthetic oils such as higher alkylbenzene, higher alkylnaphthalene, and polybutene (molecular weight of about 300 Lubricating oils containing so-called lubricating additives such as antioxidants, antiwear agents, oil agents, detergent dispersants, etc., when the dispersion concentration of ferrite fine particles in the finally obtained magnetic fluid is about It is used in such a ratio that it becomes 10 to 50% by weight.

The dispersion treatment with the addition of the low-vapor-pressure base oil is carried out by using at least one of a homogenizer, an ultrasonic wave, a vibration mill and the like as in a conventional method. After the dispersion treatment, purification is performed by centrifugation or standing in a magnetic field gradient.
Dispersion treatment can also be performed without passing through a drying step after the adsorption treatment and washing.In that case, from the viewpoint of controlling the dispersion concentration of the magnetic fluid and the evaporation component, the obtained magnetic fluid is subjected to a heat treatment under reduced pressure, It is preferable to distill low boiling components.

[0019]

EFFECT OF THE INVENTION The aqueous ferrite suspension has N-
A hydrocarbon solution of the polyalkylene polyamine-substituted alkenyl succinimide is added to form an emulsion under stirring conditions, and while the specific organic solvent is gradually added, the N-polyalkylene polyamine-substituted alkenyl succinimide is ferritized. By adsorbing on fine particles, it is possible to produce magnetic fluids in which magnetic particles are dispersed stably and easily in low vapor pressure base oil, which is a necessary condition for various applications including magnetic fluid seals. Can be.

Moreover, since the magnetic fine particles can be dispersed in the low-vapor-pressure base oil at a high concentration of about 40 to 50% by weight,
The saturation magnetization of the magnetic fluid can also be increased.

In addition, the method of the present invention is suitably applied to fine particles of a coprecipitated ferrite, and is free from the limitation that only the water-soluble surfactant which was the weakest point in the coprecipitated method can be used.

[0022]

Next, the present invention will be described with reference to examples.

Example 1 To 1850 ml of an aqueous solution in which 184 g of FeCl ₂ .4H ₂ O and 500 g of FeCl ₃ .6H ₂ O were dissolved, a 6N NaOH aqueous solution was added dropwise with stirring until the pH reached 11, and then at 80 ° C. After aging for 5 minutes and cooling, the salt was removed by decantation to obtain a magnetite suspension (magnetite concentration 10% by weight).

To 45 ml of this suspension was added 100 ml of a 0.1 molar solution of polybutenyl succinimide tetraethylenepentamine-toluene, and the mixture was poured into a 300-ml round-bottom separable flask using a propeller having a diameter of 50 mm for 800 rpm.
Stir at pm to form an emulsion. This emulsion was stirred at 50 ° C. for 60 minutes while dropping acetone at a dropping rate of 1 ml / min. Then, using a rotary evaporator, acetone, water and toluene are distilled off while heating to 50 ° C. under reduced pressure, and the residual magnetite fine particles are washed five times with a toluene-acetone (1: 1) mixed solvent and dried. I let it.

To 6.0 g of the obtained polybutenylsuccinimide tetraethylenepentamine-coated magnetite, 10.0 g of alkylnaphthalene was added, followed by stirring using a homogenizer (Excel automatic homogenizer DX, manufactured by Nippon Seiki Seisaku-sho, Ltd.) (10000 rpm, The mixture was subjected to ultrasonic dispersion treatment for further 12 hours, and centrifuged (5000 G, 30 minutes) to remove precipitates, thereby obtaining a magnetic fluid having a saturation magnetization (16 K Oe) of 290 G.

Example 2 100 ml of a 0.2 molar polybutenylsuccinimide tetraethylenepentamine-n-hexane solution was added to 60 ml of the magnetite suspension obtained by the method described in Example 1, and the procedure was the same as in Example 1. The mixture was stirred under the above stirring conditions to form an emulsion. Add 1 ml /
The mixture was stirred for 60 minutes while ethanol was added dropwise at a rate of 1 minute. Then, use an evaporator to reduce the pressure to 60
While heating to ℃, ethanol, water and n-hexane were distilled off, and the residual magnetite fine particles were washed five times with a xylene-acetone (1: 1) mixed solvent and dried.

After 5.0 g of alkylnaphthalene was added to 5.0 g of the obtained polybutenylsuccinimide tetraethylenepentamine-coated magnetite, a dispersion treatment was performed by ultrasonic irradiation for 24 hours, followed by centrifugation (5000 G, 30 minutes). The precipitate was removed to obtain a magnetic fluid having a saturation magnetization of 440G.

COMPARATIVE EXAMPLE 1 To a suspension of magnetite obtained by the method described in Example 1 was added 100 ml of a solution of polybutenyl succinimide tetraethylenepentamine-toluene having a concentration of 0.005 mol and stirred. No emulsion was formed,
The mixture was directly treated at 60 ° C. for 60 minutes, and then water and toluene were distilled off while heating to 50 ° C. under reduced pressure using an evaporator, and the residual magnetite fine particles were removed with a toluene-acetone (1: 1) mixed solvent. Washed and dried twice.

After adding 5.0 g of alkylnaphthalene to 3.0 g of the obtained magnetite fine particles, the mixture was stirred (10000 rpm, 60 minutes) using a homogenizer, and further subjected to a dispersion treatment by ultrasonic irradiation for 12 hours, followed by centrifugation (5000 G). , 30 minutes) to remove the sediment, resulting in an almost transparent supernatant.

Comparative Example 2 In Example 1, when the stirring treatment was performed without adding acetone, the saturation magnetization of the obtained magnetic fluid was 240 G.

Claims (2)

(57) [Claims] 1. An N-polyalkylenepolyamine-substituted alkenyl succinimide hydrocarbon solution is added to an aqueous suspension of ferrite fine particles, and the N-polyalkylene polyamine-substituted alkenyl succinic acid is miscible with the hydrocarbon solvent. While gradually adding an organic solvent in which the imide is hardly soluble or insoluble, the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed to the ferrite fine particles, and then the organic solvent, water and the hydrocarbon solvent are distilled off. And dispersing the residual N-polyalkylene polyamine-substituted alkenyl succinimide-adsorbed ferrite fine particles in a low-vapor-pressure base oil having a vapor pressure of 0.1 mmHg or less at 25 ° C. . 2. An aqueous suspension of ferrite fine particles is added with a hydrocarbon solution of N-polyalkylene polyamine-substituted alkenyl succinimide to form an emulsion under stirring conditions. By gradually adding an organic solvent in which the N-polyalkylenepolyamine-substituted alkenyl succinimide is hardly soluble or insoluble, the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed on ferrite fine particles. The method for producing a magnetic fluid according to claim 1.