JP3045181B2 - 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 are dispersed one by one without agglomeration. It is necessary to adsorb a hydrophilic surfactant to the surface of the fine particles.

[0004] By the way, magnetic fine particles having a water-soluble surfactant adsorbed thereon disperse well in relatively volatile solvents such as kerosene and toluene, but have high dispersibility in low vapor pressure base oils. It is not practical and not practical for the production of magnetic fluids.

[0005] In order to improve such a point, a method in which an oil-soluble surfactant is directly adsorbed on magnetic fine particles is considered. According to the conventional method, since the magnetic fine particles are hydrophilic, a method of drying the magnetic fine particles and then simultaneously performing a pulverizing step using a ball mill or the like and an adsorption step of the oil-soluble surfactant is adopted. It takes a long time, and the yield is deteriorated due to aggregation of particles in the drying step.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to use ferrite fine particles having an oil-soluble surfactant adsorbed thereon,
It is an object of the present invention to provide a method for producing a magnetic fluid in which it is dispersed in a low vapor pressure base oil with good dispersibility.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
To an aqueous suspension of ferrite fine particles, an oil-soluble surfactant is added as a solution in a hydrocarbon solvent azeotropic with water, and the oil-soluble surfactant is adsorbed on the ferrite fine particles. Azeotropically removed, there
In this method, a low-vapor-pressure base oil having a vapor pressure of 0.1 mmHg or less is added, the dispersion treatment is performed, and then the hydrocarbon solvent is distilled off under reduced pressure to produce a magnetic fluid.

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 oil-soluble surfactant, N-polyalkylene polyamine-substituted alkenyl succinimides, mono-
Or a di-oxyalkylene group-containing phosphate ester or a mixture thereof, or oleic acid, linoleic acid,
Linolenic acid, aliphatic carboxylic acids such as erucic acid, C ₁₂ -C
₂₄ aliphatic sulfonic acids or sulfates, alkylbenzene sulfonic acids having an alkyl group of ₆ or more,
At least two types are used in combination. The selection of the combination depends on the affinity with the magnetic fluid base oil used.

As the N-polyalkylene polyamine-substituted alkenyl succinimide, the following are used. 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

The following are used as the mono- or di-oxyalkylene group-containing phosphoric acid ester. R: alkyl phenyl group having an alkyl group of the alkyl group C ₅ -C ₁₀ of _{C 6 ~C 18 n: 2~3 m} : 4~10

These oil-soluble surfactants can be used in aliphatic or aromatic hydrocarbon solvents having a boiling point of about 80 to 200 ° C. which are compatible with and azeotrope with water, such as undecane, toluene and xylene. About 0.01 to 0.5 mol, preferably about
It is used as a solution dissolved at a concentration of 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 oil-soluble surfactant is adsorbed to the ferrite fine particles at the interface of the emulsion, but in order to rapidly perform this adsorption, a temperature condition of about 40 to 90 ° C. Is desirably stirred for about 30 to 60 minutes.

Thereafter, azeotropic removal of water under normal pressure is performed. The removal of water under normal pressure is performed by performing a stirring treatment under a temperature condition of about 40 to 80 ° C. for about 0.5 to 1.5 hours, and azeotropically evaporating water with a hydrocarbon. At that time, an amount of hydrocarbon corresponding to the azeotropic amount is further added in advance, and azeotropic distillation is performed.

A hydrocarbon dispersion of oil-soluble surfactant-adsorbed magnetic fine particles from which water has been removed azeotropically has a viscosity of 0.1 mmH at 25 ° C.
A low-vapor-pressure base oil having a vapor pressure of not more than g is added, and a dispersion treatment using a homogenizer or ultrasonic waves is performed.

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.

Thereafter, the hydrocarbon solvent is distilled off under reduced pressure to form a magnetic fluid in which magnetic fine particles are well dispersed in a low vapor pressure base oil.

[0018]

According to the method of the present invention, an oil-soluble surfactant is added to a ferrite aqueous suspension as a solution dissolved in a hydrocarbon solvent azeotropic with water, and an emulsion is formed under stirring conditions. By adsorbing a soluble surfactant onto ferrite fine particles, a magnetic fluid in which magnetic particles are stably and easily dispersed in a low vapor pressure base oil, which is a necessary condition for magnetic fluid seals and other various applications, can be obtained. Can be manufactured.

Moreover, after the adsorption treatment of the oil-soluble surfactant,
By azeotropically removing water under normal pressure, oil-soluble surfactant-adsorbed magnetic fine particles dispersed in a hydrocarbon solvent are obtained.After mixing with a low vapor pressure base oil, the hydrocarbon solvent is removed under reduced pressure. By distilling off, a magnetic fluid having excellent dispersibility can be efficiently produced.

[0020]

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

Comparative Example A 6N NaOH aqueous solution was added dropwise 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 until the pH reached 11, and then at 80 ° C. for 30 minutes. Aged, cooled and the salts were removed by decantation. Thereafter, 500 ml of distilled water was added and the mixture was stirred and washed, and the operation of removing the supernatant by decantation was repeated three times to obtain a magnetite suspension (magnetite concentration: 25 to 30% by weight).

To 15 ml of this suspension was added 100 ml of a 0.1 molar solution of polybutenylsuccinimide tetraethylenepentamine-toluene, and the volume was 300 m at 60 ° C. for 60 minutes.
In a 1 l round-bottom separable flask, stirring was performed at 800 rpm using a 50 mm diameter propeller to form an emulsion. Then, using a rotary evaporator, under reduced pressure
While heating to 50 ° C., water and toluene were distilled off, and the residual magnetite fine particles were washed five times with a toluene-acetone (1: 1) mixed solvent and dried.

After adding 5.0 g of alkylnaphthalene to 3.0 g of the obtained polybutenylsuccinimide tetraethylenepentamine-coated magnetite, the mixture was stirred 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, centrifuged (5000 G, 30 minutes) to remove sediment, and a magnetic fluid having a saturation magnetization (16 K Oe) of 250 G was obtained.

Example 6 To 15 ml of the magnetite suspension obtained by the method described in the comparative example, 6 mmol of polybutenylsuccinimide tetraethylenepentamine and 60 ml of an n-hexane solution were added, and the mixture was heated at 80 ° C. for 60 minutes. The mixture was stirred under the same stirring conditions to form an emulsion. Then, 100 ml of toluene
And heated to about 90 ° C. under normal pressure to azeotropically remove water.

To the remaining toluene dispersion of polybutenylsuccinimide tetraethylenepentamine-adsorbed magnetite was added 15 g of alkylnaphthalene, and the mixture was stirred (10000 rpm, 60 minutes) using a homogenizer, and further ultrasonically treated for 8 hours. Distributed processing was performed.

Thereafter, toluene was distilled off under reduced pressure, and the precipitate was removed by centrifugation (5000 G, 30 minutes).
G magnetic fluid was obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-228536 (JP, A) JP-A-1-207131 (JP, A) JP-A-57-144028 (JP, A) JP-A-54-1979 65182 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01F 1/44

Claims (2)

(57) [Claims] 1. A method in which an oil-soluble surfactant is added to an aqueous suspension of ferrite fine particles as a solution in a hydrocarbon solvent azeotropic with water, and the oil-soluble surfactant is adsorbed on the ferrite fine particles. Azeotropically removing water under normal pressure, adding a low-vapor-pressure base oil having a vapor pressure of 0.1 mmHg or less at 25 ° C., dispersing, and distilling off the hydrocarbon solvent under reduced pressure. A method for producing a magnetic fluid. 2. An oil-soluble surfactant is added to an aqueous suspension of ferrite fine particles as a solution in which an oil-soluble surfactant is dissolved in a hydrocarbon solvent azeotropic with water, and an emulsion is formed under stirring conditions. 2. The method for producing a magnetic fluid according to claim 1, wherein the activator is adsorbed on ferrite fine particles.