JP3045183B2 - 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.
After irradiating the aqueous suspension of ferrite fine particles with ultrasonic waves, an N-polyalkylene polyamine-substituted alkenyl succinimide hydrocarbon solution is added thereto, and the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed to the ferrite fine particles. After the water and hydrocarbon solvent is distilled off, the residue N- polyalkylene polyamine substituted alkenyl succinimide adsorption ferrite fine particles,
It is achieved by producing a magnetic fluid by dispersing in a low vapor pressure base oil having a vapor pressure of 0.1 mmHg or less at 25 ° C.

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.

In order to minimize the aggregation of ferrite fine particles in the aqueous phase and to efficiently adsorb the N-polyalkylene polyamine-substituted alkenyl succinimide to the ferrite fine particles, the formed aqueous suspension is It is used after irradiating ultrasonic waves for about 0.5 to 10 hours. The ultrasonically irradiated aqueous suspension is immediately mixed with a hydrocarbon solution of N-polyalkylene polyamine-substituted alkenyl succinimide after irradiation.

The following are used as the N-polyalkylenepolyamine-substituted alkenyl succinimide. (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

[0012] N-polyalkylene polyamine-substituted alkenyl succinimides can be prepared from aliphatic, alicyclic or aromatic hydrocarbon solvents having a boiling point of about 60 to 200 ° C., such as n-hexane, n-heptane, n-octane, Isooctane , n-decane, cyclohexane, toluene, xylene, mesitile
Emissions, petroleum ether, petroleum benzine, ligroin, etc. naphtha, about 0.01 to 0.5 mol, preferably used as a solution dissolved at a concentration of about 0.1 to 0.5 moles.

[0013] These organic solvent 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.

Thereafter, water and the hydrocarbon solvent are distilled off, and the residue is subjected to 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.

[0018]

According to the method of the present invention, an aqueous suspension of ferrites is irradiated with ultrasonic waves in advance, then a hydrocarbon solution of N-polyalkylene polyamine-substituted alkenyl succinimide is added, and an emulsion is formed under stirring conditions. By adsorbing N-polyalkylenepolyamine-substituted alkenyl succinimide to ferrite fine particles, magnetic particles can be stably and easily applied to low vapor pressure base oil, which is a necessary condition for various applications including magnetic fluid seals. Can be produced with good efficiency.

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 a water-soluble surfactant which is the weakest point in the coprecipitated method can be used.

[0021]

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).

Immediately after irradiating the suspension with ultrasonic waves for 1 hour, 100 ml of a 0.1 molar polybutenylsuccinimide-tetraethylenepentamine-toluene solution was added to 45 ml of the suspension, and a volume of 300 ml was added at 60 ° C. for 60 minutes. Using a 50 mm diameter propeller in a round bottom separable flask
The emulsion was formed by stirring at 0 rpm. Thereafter, using a rotary evaporator, water and toluene were distilled off while heating to 50 ° C. under reduced pressure, and the residual magnetite fine particles were washed five times with a toluene-acetone (1: 1) mixed solvent and dried. .

To 3.0 g of the obtained polybutenylsuccinimide tetraethylenepentamine-coated magnetite, 5.0 g of alkylnaphthalene was added, and the mixture was stirred using a homogenizer (Excel automatic homogenizer DX, manufactured by Nippon Seiki Seisaku-sho, Ltd.) (10000 rpm, (60 minutes), followed by dispersion treatment with ultrasonic waves for further 12 hours, and centrifugation (5000 G, 30 minutes) to remove precipitates to obtain a magnetic fluid having a saturation magnetization (16 K Oe) of 280 G.

Example 2 A 60 ml suspension of magnetite obtained by the method described in Example 1 was irradiated with ultrasonic waves for 3 hours, and then a 0.2 mol polybutenyl succinimide tetraethylenepentamine-n- Add 100 ml of hexane solution, and at 40 ° C for 60 minutes,
The mixture was stirred under the same stirring conditions as in Example 1 to form an emulsion. Then, using an evaporator, under reduced pressure
Water and n-hexane were distilled off while heating to 60 ° C., and the residual magnetite fine particles were washed five times with a xylene-acetone (1: 1) mixed solvent and dried.

After adding 5.0 g of alkylnaphthalene to 5.0 g of the obtained polybutenylsuccinimide tetraethylenepentamine-coated magnetite, a dispersion treatment by ultrasonic irradiation was performed for 24 hours, followed by centrifugation (5000 G, 30 minutes). The sediment was removed to obtain a magnetic fluid having a saturation magnetization of 420 G.

Example 3 A 50 ml suspension of magnetite obtained by the method described in Example 1 was irradiated with ultrasonic waves for 3 hours, and then a 0.4 molar polybutenyl succinimide tetraethylenepentamine-ligroin solution was added thereto. Add 100 ml, 30 minutes at 70 ℃,
The mixture was stirred under the same stirring conditions as in Example 1 to form an emulsion. Then, using an evaporator, under reduced pressure
While heating to 60 ° C, water and ligroin are distilled off, and the residual magnetite fine particles are dissolved in toluene-methanol (1: 1).
Washed 5 times with the mixed solvent and dried.

After adding 4.0 g of alkylnaphthalene to 4.0 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 sediment was removed to obtain a magnetic fluid having a saturation magnetization of 430G.

COMPARATIVE EXAMPLE To 15 ml of the magnetite suspension obtained by the method described in Example 1, 100 ml of a 0.005 molar concentration polybutenylsuccinimide tetraethylenepentamine-toluene solution was added 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.

To 3.0 g of the obtained magnetite microparticles, 5.0 g of alkylnaphthalene was added, followed by stirring (10000 rpm, 60 minutes) using a homogenizer, followed by dispersion treatment by ultrasonic irradiation for 12 hours, and centrifugation (5000 G). , 30 minutes) to remove the sediment, resulting in an almost transparent supernatant.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-302705 (JP, A) JP-A-61-189607 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 1/44

Claims (2)

(57) [Claims] After irradiating an aqueous suspension of ferrite fine particles with ultrasonic waves, a hydrocarbon solution of N-polyalkylene polyamine-substituted alkenyl succinimide is added thereto, and N-polyalkylene polyamine-substituted alkenyl succinimide is added. After being adsorbed on the ferrite fine particles, the water and the hydrocarbon solvent are distilled off. A method for producing a magnetic fluid, comprising dispersing in a pressurized base oil. 2. After irradiating the aqueous suspension of ferrite fine particles with ultrasonic waves, an N-polyalkylene polyamine-substituted alkenyl succinimide hydrocarbon solution is added thereto, and an emulsion is formed under stirring conditions. 2. The method for producing a magnetic fluid according to claim 1, wherein the N-polyalkylene polyamine-substituted alkenyl succinimide is adsorbed on ferrite fine particles.