JPS5889802A - Manufacture of magnetic fluid - Google Patents

Abstract

PURPOSE:To simplify the manufacture of magnetic fluid which is excellent in producibility, stable dispersibility, and saturated magnetizing force by a method wherein unsaturated fatty acid and alicyclic carboxylic acid are used as carboxylic acid in the proper percentage of mixture. CONSTITUTION:In a reactor having an oridinary agitator, an ion salt solution is dripped into and stirred up in an NaOH solution, the reaction product is heated up and aged. The pH of a reaction system is turned to approximately 12. Aqueous solution of potassium erucic salt and aqueous solution of sodium naphthenic salt are mixed while the agitation is being continued, the above is put in a reaction product and aged. The pH of the mixture is turned to approximately 12. While stirring up the mixture, H2SO4 solution is added, and after the pH has been completely stabilized, fluidized paraffin and alkyl benzene are added. When the agitation is continued, carboxylic acid adsorbed magnetite is settled to the under layer. When the agitation is stopped, magnetic fluid is separated to the lower layer and a byproduct salt solution to the upper layer. The obtained magnetic fluid is centrifugally separated, and after a sediment has been removed, the magnetic fluid is obtained by adjusting the consistency of the mixture of fluidized paraffin and alkyl benzene.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing magnetic fluids.

Here, magnetic fluid refers to a liquid ferromagnetic material in which ultrafine magnetic particles with a particle size of about 100A are stably dispersed in a solvent, and is a unique material that has both fluid properties and ferromagnetic properties. be.

The reality is that magnetic fluids have only recently been developed and their application technology has not been sufficiently developed, but their unique physical properties have attracted attention in many technical fields and are a material that is expected to develop in the future. be.

The reasons why the development of applied technology for magnetic fluids was delayed were that there was no suitable method for manufacturing magnetic fluids, the existence of magnetic fluids themselves was not well known, and the manufacturing method was unsuitable for industrial production and was unprofitable. This is due to the fact that the magnetic fluid used was extremely expensive.

The basic performance that a magnetic fluid should have is (1) Strong magnetic particles are stably dispersed in the fluid (dispersion stability).
, (2) low viscosity, and (3) high saturation magnetizing power.In addition, industrial magnetic fluids with excellent properties can be obtained easily and inexpensively, and with constant quality. be.

However, it is actually very difficult to obtain a magnetic fluid with excellent quality in all of the above characteristics, and none of the methods proposed so far are necessarily satisfactory.

For example, Japanese Patent Publication No. 53-217118 discloses a method for producing a magnetic fluid in which unsaturated fatty acids are adsorbed onto a ferromagnetic oxide and dispersed in oil. In this method, only a relatively large amount of unsaturated fatty acids are used as callebonate to be adsorbed on a ferromagnetic oxide, and the resulting fatty acid-adsorbed ferromagnetic oxide is once coagulated and dehydrated, and then dispersed in oil.

In this method, the steps of agglomeration, washing, and dehydration of the fatty acid-adsorbing ferromagnetic oxide are extremely difficult to operate, and there are problems with industrial profitability. It is not possible to increase the content of ferromagnetic oxide in the magnetic fluid because iron is formed and the saturation magnetizing power decreases, and the viscosity of the generated magnetic fluid becomes high. Therefore, the saturation magnetizing power is high. One point is that it is difficult to obtain a magnetic fluid. In Japanese Patent Application Laid-open No. Sho SA-ES1G-Z, alkali is added to ferrous and ferric salts to adjust the pH to 7.0 to 8.5. A method for producing a magnetic fluid is disclosed in which a monomolecular film of unsaturated fatty acids is formed on the surface of the obtained colloidal particles, and this is transferred to a water-insoluble organic solvent layer.

This method is industrially very advantageous in that it transfers the fatty acid-adsorbed particles to the organic solvent layer without washing, dehydrating, or drying them. However, in this method, an alkali is added to the iron salt aqueous solution and unsaturated fatty acids are adsorbed at a relatively low OPH, so this seems to be because the quality of the magnetic particles is poor and no ferromagnetic material is formed, but it is satisfactory. Saturation magnetization cannot be obtained (for example, in one example, 165 ga at a solid concentration of 46%,
). Furthermore, this method requires severe conditions in order to separate the organic solvent layer from the aqueous phase when transferring the magnetic particles from the aqueous phase to the organic solvent phase. There are also problems with the iron oxide content and dispersion stability in the magnetic fluid.

Japanese Patent Publication No. 54-38987 by the present inventors discloses a method in which carboxylic acid is added to colloidally dispersed iron oxide in an unneutralized state and adsorbed, and this is transferred to a water-insoluble organic solvent phase. is disclosed.

This method is characterized by adsorption of carboxylic acid onto iron oxide in an unneutralized state, which is extremely effective in terms of obtaining a magnetic fluid with low viscosity and high saturation magnetizing force. This is the preferred method.

However, even with this method, the saturation magnetization amount is at most about 300 Gauss, which is insufficient to obtain even higher magnetizing power, for example, about 400 Gauss. As a result, the ferromagnetic fine particle dispersion is always produced under strong alkaline conditions, for example, pH 10 or higher, preferably 11 or higher, particularly 12 or higher, and carboxylic acid adsorption is also carried out while maintaining this alkaline condition, i.e. When the carboxylic acid to be added is also made into a strong alkali salt and monomolecular adsorption is performed, and the obtained carboxylic acid-adsorbed ferromagnetic particles are used to make a magnetic fluid, it has a significantly high saturation magnetizing force and a low viscosity. It was found that this can be obtained. However, in this method, when the carboxylic acid-adsorbed ferromagnetic particles are transferred to a water-insoluble organic solvent, -1 aggregates are generated, making it very difficult to separate the oil phase and the aqueous phase, which poses a problem in industrial practicality.

As a result of further research by the present inventors, we found that if unsaturated fatty acids and alicyclic carboxylic acids are used as carboxylic acids in an appropriate ratio in the above method, the oil phase will be It has been found that it is possible to obtain a magnetic fluid in which the aqueous phase is easily separated, has excellent industrial productivity, and has excellent dispersion stability, viscosity, and saturation magnetization force.

That is, the present invention adds an aqueous solution of a metal salt capable of forming a ferromagnetic substance to an alkaline aqueous solution while maintaining the pH at 10 or higher to form a ferromagnetic fine particle dispersion, and substantially coats the surface of the ferromagnetic fine particles. An aqueous salt solution of a mixed fatty acid of an aliphatic unsaturated carboxylic acid having 18 or more carbon atoms and an alicyclic carboxylic acid having 7 or more carbon atoms is mixed in an amount to form a single molecular layer, and then the pH is adjusted to 6 or less using an acid. A dispersion of carboxylic acid-adsorbed hydrophobic ferromagnetic particles is obtained, and a dispersion organic solvent is added to this to transfer the carboxylic acid-adsorbed hydrophobic ferromagnetic particles to the hydrophobic organic solvent layer. A method for producing a fluid is provided.

In the present invention, while maintaining the pH of the alkaline aqueous solution at 10 or higher, particularly 12 or higher, adding an aqueous solution of a metal salt capable of forming a ferromagnetic substance to the alkaline aqueous solution creates a ferromagnetic fine particle dispersion.
This is an important requirement in forming the The pH is lower than 10, or an alkaline aqueous solution is added to an aqueous solution of a metal salt that can form a ferromagnetic substance, and the final pH is adjusted to
Even if it is adjusted to 10 or more, especially 12 or more, fine magnetic particles and particle dispersion cannot be obtained, and adsorption of carboxylic acid becomes insufficient, and as a result, the hydrophobic organic solvent of the magnetic particles The migration and dispersibility of the product decreases. Furthermore, it is not possible to obtain a magnetic fluid with a high content of magnetic particles and a relatively low viscosity. On the other hand, according to the above method, the magnetic particles take on a spinel structure, and the saturation magnetizing force is improved.

The alkalis used in the present invention include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide,
Alternatively, organic water-soluble amines may be used, but sodium hydroxide or potassium hydroxide is particularly preferred.

Salts of metals that can form ferromagnets are not limited, but include ferrous iron, ferric iron, zinc, manganese, nickel, chlorides, sulfates, and the like. The above salt aqueous solution is added to an alkaline aqueous solution while stirring to form an oxide of the above metal. The metal oxide is ferrite, magnetite, etc., for example, F
eo < □−n ) −Fe2o3In), FeO(
1-n) *ZnO,n, -Fe2O3,Mn0(
t-n) -Zn0(n) #Fe2O3,N"(1-
”) ” ”0(nl' Fe2O3・C00(1-n
) "The content is preferably adjusted to about 2 to 15% by weight.

The type and amount of carboxylic acid to be adsorbed onto the surface of the ferromagnetic particles is one of the important requirements in the present invention.

As the carboxylic acid, a mixture of an aliphatic unsaturated carboxylic acid having 18 or more carbon atoms and an alicyclic carboxylic acid having 7 or more carbon atoms is used.

Examples of fatty acid unsaturated carboxylic acids include oleic acid, linoleic acid, -elaidic acid, and erucic acid. Among those having a large molecular weight, erucic acid is particularly preferred. Alicyclic carboxylic acids include naphthenic acid, abietic acid, etc. Naphthenic acid, especially acid value 100-300°, preferably 160-2
40 naphthenic acids are preferred.

The ratio of aliphatic unsaturated carboxylic acid to alicyclic carboxylic acid is varied depending on the type of hydrophobic organic solvent in which the magnetic particles are dispersed. When the hydrophobic organic solvent contains a large amount of alicyclic compounds or aromatic compounds, it is preferable to use a large amount of alicyclic carboxylic acid. Usually the blending ratio of both is 2/8 to 8/2 by weight.
It is preferable to select from the range of (aliphatic/alicyclic).

By using the above mixed carboxylic acid, a dense carboxylic acid layer is formed on the surface of the magnetic particles, and the dispersion stability of the produced magnetic fluid is significantly improved. What is particularly important is that the fine-structured magnetic particles produced under strong alkaline conditions as in the present invention are difficult to absorb when trying to transfer carboxylic acid adsorbates to a hydrophobic organic solvent phase without dehydrating them. The water in the adsorbate emulsifies with the hydrophobic organic solvent, making separation of the two very difficult and almost impractical from an industrial perspective. Furthermore, even if the separation is successful, a large amount of water and by-product salts will be mixed into the magnetic fluid, requiring post-treatment such as dehydration means such as J vacuum distillation and means for removing by-product salts. Such post-processing steps not only reduce industrial profitability, but also
This is not preferable because it oxidizes metal oxides, especially ferrous iron, in the magnetic fluid and reduces the saturation magnetizing power.

In the present invention, an aliphatic unsaturated carboxylic acid layer is used as a hydrophobic organic solvent for magnetic particles by using a combination of carboxylic acid, especially erucic acid and naphthenic acid, and by appropriately adjusting the blending ratio. can be easily achieved without emulsification. Furthermore, the water content in the obtained magnetic fluid is low, and it is possible to almost eliminate oxidation of magnetic particles and contamination of by-product salts that occur during the dehydration process.

Furthermore, the thermal stability of the obtained magnetic fluid is significantly improved. For example, a conventional magnetic fluid obtained by adsorption of an unsaturated fatty acid such as oleic acid alone causes dispersion destruction at 120°C for 30 minutes, but when adsorbing a mixed carboxylic acid of erucic acid and naphthenic acid, it takes 100 hours at 150°C. Thus, it is possible to obtain a stable magnetic fluid.

The amount of carboxylic acid used is such that a substantially monomolecular film of carboxylic acid is formed on the surface of the magnetic particles 1. As the amount of carboxylic acid increases, the viscosity of the produced magnetic fluid increases, making it difficult to obtain a magnetic fluid containing many magnetic particles. Further, as the amount is smaller than that, the transfer of the magnetic particles to the hydrophobic solvent becomes incomplete, and the dispersion stability of the generated magnetic fluid decreases.

Adsorption of carboxylic acid to the surface of magnetic particles occurs at pH 10 or higher.
Preferably it is 11 or more, particularly preferably 12 or more. Therefore, it is preferable to use a strong alkali salt solution of carboxylic acid, such as sodium salt or potassium salt, which is the same alkali salt solution used to form the ferromagnetic fine particle dispersion, but the concentration of the carboxylic acid alkali salt aqueous solution is 5. The amount is preferably 40% by weight, and if desired, lower alcohols such as methanol and ethanol, alkylene glycols, etc. may be added in small amounts.

The adsorption of carboxylic acid may be carried out by adding an aqueous solution of an alkali carboxylic acid salt to the ferromagnetic fine particle dispersion, or may be reversely divided.

The adsorption step can be carried out by ordinary stirring and no special measures are required.

After adsorption of the carboxylic acid, acid is added to the aqueous dispersion of the product to adjust the pH to below 6, preferably to pH 5.5±0.2.

As the acid, in addition to inorganic acids such as hydrochloric acid and sulfuric acid, lower organic acids such as acetic acid and lactic acid may be used.

After addition of the acid, a carboxylic acid-adsorbed hydrophobic ferromagnetic fine particle dispersion is obtained, and this dispersion is transferred to a predetermined hydrophobic organic solvent. When a hydrophobic organic solvent is added to the dispersion, the hydrophobic ferromagnetic fine particles immediately migrate to the hydrophobic organic solvent to form a magnetic fluid. This material is washed with water if necessary, and then residual water is distilled off under reduced pressure.

Any desired solvent may be used as the hydrophobic organic solvent, but typically hydrocarbon-based solvents such as n-hexane, cyclohexane, kerosene, paraffin oil, machine oil, motor oil, lubricating oil, and diffusion pump oil are used. It is a solvent.

According to the method of the present invention, not only is it extremely easy to manufacture magnetic fluids, but the obtained magnetic fluids are significantly superior in dispersion stability, viscous properties, and saturation magnetizing force compared to those obtained by conventional methods. There is.

For example, regarding dispersion stability, centrifugal purification for 30 minutes is possible with 2100g (13°△ 000rpm) classification.
Even if placed in a magnetic field of 600 Gauss for 24 hours, the magnetic field concentration is 1
% or more. Furthermore, a product that does not separate even when heated at 150° C. for 100 hours or more can be obtained.

Furthermore, regarding the viscosity properties, the magnetic particle content is 45 to 46.
Weight% (ash content equivalent) 10-30 (pg' (20℃)
) can be obtained, and the dispersion stability at this viscosity is extremely high.

A particularly important point is that in the present invention, a magnetic fluid with a low viscosity and a high content of magnetic particles can be obtained, and moreover, it is possible to obtain a magnetic fluid with a high content of magnetic particles during the manufacturing process, so that the magnetic particles themselves do not need to come into contact with air. Excellent magnetic properties. the result,
According to the method of the present invention, a magnetic fluid having an amazing saturation magnetization force of 400 Gauss can be obtained.

Furthermore, according to the present invention, not only magnetite but also ferrite magnetic fluids containing various metals can be easily produced.

The present invention will be explained below with reference to Examples. In the examples, parts or percentages are by weight unless otherwise specified.

Example 1 In a normal reactor with a stirrer! '4aOH (granular) 550
．． Dissolve OF in 2300 m/s of water. Separately, FeSO4・
7H20534,4f and FeC/3 (active ingredient 39
%) 1301), 8P is dissolved in water 1840- to prepare an iron salt solution.

The iron salt solution is added dropwise to the NaOH solution and stirred for 15 to 20 minutes while maintaining the reaction temperature below 40°C. The reaction product is heated to 55-60°C and aged for about 10 minutes.

The pH of the reaction system becomes approximately 12.

While continuing to stir, add salt solution (5%) to erucic acid.
0.6f! and a naphthenic acid Na salt aqueous solution (naphthenic acid acid value 20:10%) 608.42, and this was poured into the above reaction product at a temperature of 55 to 60°C and aged for 30 minutes. The pH of the mixture will be approximately 12.

While keeping the mixture at 55-60°C and continuing to stir, heat the mixture to 60-1
Over 20 minutes, add H2SO,i aqueous solution (30%) and adjust to pH 5.5±0.2. After the pH became sufficiently stable, 1. liquid paraffin (Idemitsu Oil Co., Ltd. IP-2028) 218.01 and alkylbenzene (Nissan Kagaku Co., Ltd. Kinalgene N-500) 54.
Add 46Ii (55-60°C). When stirring is continued, the carboxylic acid-adsorbed magnetite moves to the oil phase and settles to the lower layer. When stirring is stopped, the magnetic fluid is separated into the lower layer and the by-product salt aqueous solution is separated into the upper layer. The magnetic fluid layer is taken out, washed with water and separated repeatedly, and then distilled under reduced pressure to remove residual moisture. Centrifuge the obtained magnetic fluid 21.00Of,
After removing the sediment (13,000 rpm x 15 minutes), the concentration was adjusted to 45% (in terms of ash content) with a mixed oil of the above-mentioned fluidized 7-inch rough-in and alkylbenzene to obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (20℃) 20~3 Q cps specific gravity (2
0℃) 1.25-1.35 Ash content (%)
45-46 Magnetizing power (60000e) 390-420 (G) Example 2 Same as Example 1 except that neothiozole (manufactured by C12-16 hydrocarbon Chuo Kasei Co., Ltd.) was used instead of liquid paraffin and alkyl-benzene. to obtain the magnetic fluid. The physical properties of the product are shown below.

Viscosity (20℃) 10~20 CP11 specific gravity (2
0℃) 1.25-1.35 Ash content (%)
45~46 Magnetizing force (60000e) 390~4.20CG)
Example 3 Using the same reactor as Example 1, Na0H (granular) 680V
Dissolve in 3200m/ml of water. Separately F e S O,i
・7HO688,4S' and FeCl a (
Dissolve 1501.2F (39% active ingredient) in 30001 nl of water to prepare an iron salt solution.

The iron salt solution is added dropwise to the NaOH solution and stirred while maintaining the reaction temperature below 40°C. The reaction product is heated to about 30% at room temperature.
Let rise for a minute. The pH of the reaction system is maintained at about 12 or higher.

Erucic acid with salt aqueous solution (5%) 1512. OF and naphthenic acid Na salt aqueous solution (naphthenic acid acid value 22o; 10%) 74
3.2ti, and added to the above reaction product at room temperature and aged for 30 minutes. The pH of the mixture will be approximately 12.

Keep the mixture at room temperature and continue stirring for 120 minutes.
Add H2SO4 aqueous solution (30%) to pH 5.5 ± 0.
．． Adjust to 2. After the pH becomes sufficiently stable, synthetic oil (
Lion Corporation - Add 302.5y of diffusion pump oil 5) and raise the temperature to about 80-85°C. Carboxylic acid adsorbed magnetite migrates to the oil phase. After stopping stirring, the magnetic fluid separated into the lower layer is taken out, washed with water, and residual water is distilled off under reduced pressure. The obtained magnetic fluid was centrifuged. 21,0OOI! , 1
3,000 rpm x 15 minutes) to remove sediment.゛The physical properties of the product are as follows. This one is 15
It remained stable even after continued heating at 0°C for 100 hours. - Viscosity (20℃) 800-1300cps Specific gravity (20℃) 1.35-1.50 Ash content (%)
42-48 Magnetizing power (60000e) 380-440 (G) Example 4 NaOH (granular (95%),) 55° 4g water about 2
Dissolves in 100-. Separately, Fe5o4-7H20 (industrial 95%) 534.4f! An iron salt solution is prepared by dissolving 1300.89 ml of FeC/3 (active ingredient 39%) in about 1500 m/m of water.

The iron salt solution was added dropwise to the NaOH solution and stirred for 13 minutes while maintaining the reaction temperature below 40°C.

The reaction product is warmed to 40-45°C and aged for about 10 minutes. The pH of the reaction system will be approximately 11-12.

Erucic acid with salt aqueous solution (5%) 141.8SI and naphthenic acid Na salt aqueous solution (naphthenic acid acid value 200.:11)%
) 7279 and added to the above reaction product at room temperature and aged for 10 minutes. The pH of the mixture will be 11-12.

While keeping the mixture at 40-45°C and continuing stirring, an aqueous H2SO4 solution (30%) was added over 60 minutes, and the pH was adjusted to 5.5.
Adjust to ±0.2 to obtain aggregates. After the pti becomes sufficiently stable, add hexane 2732 to it (40-45
℃). Carboxylic acid adsorbed magnetite in the dispersion migrates to the oil phase. Water is removed by settling, washed twice with water, and after water separation, residual water is distilled off under reduced pressure. The obtained magnetic fluid was centrifuged at 21,0 OOP, 13000 rPm.
After removing the sediment (X 15 minutes), the concentration was adjusted to 45% (calculated as ash) with the above hexane to obtain a magnetic fluid.

The physical properties of the product are as follows.

Viscosity (40℃) 43.1 cps Specific gravity, -(2
0℃) 1.353 Ash content (%)
45% Magnetizing force (60000e) 410 (G) Example 5 N a OH' (granular) 552Ii in 2100ml of water
dissolve in Separately, Fe3O4・7H20 (95% for industrial use)
) 599.5 f! and FeC13 (active ingredient 39
%) 1138.2F in water 1470- to prepare an iron salt solution.

The iron salt solution was added to the NaOH solution at a reaction temperature of 37° C. for aging. The pH of the reaction system becomes approximately 11.1.

Erucic acid with salt aqueous solution (5%) 124of! and Naphthenic acid salt aqueous solution (S7thenic acid acid value 200:10%) 63
6y and add it into the above reaction product. The pH of the mixture becomes lO~11. Add H2SO4 aqueous solution (30%) over 60 minutes while continuing to stir, and adjust the pH to 5.
Adjust to 5±0.2. After the pH becomes sufficiently stable, n-hexadecane 2711i is added thereto at 80° C. over 50 minutes. Carboxylic acid adsorbed magnetite migrates to the oil phase. Water is removed by settling, washed twice with water, and after water separation, residual water is distilled off under reduced pressure. The obtained magnetic fluid was centrifuged at 21,000 g and 13,000 rpm x 1.
After removing the sediment (for 5 minutes), the concentration was adjusted to 45% (calculated as ash) with n-hexadecane to obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (40℃) 13 CPS specific gravity (20℃)
1.308 Ash content (%) 45 Magnetizing power (60000e) 433 (G) Example 6 N a OH (granular) 6929 was added to water 3000. n! dissolve in Separately, an iron salt solution is prepared by dissolving 668y of F e SO4.7 H2O and 1626.9 of F e Cj'3 (39% active ingredient) in 2100 - of water.

Add the iron salt solution to the NaOH solution at a reaction temperature of 25 to 40°C.
The mixture was added dropwise and stirred for 17 minutes. The reaction product is heated to 60°C and aged for about 30 minutes. The pH of the reaction system becomes approximately 12.

Aqueous salt solution (5%) of lucic acid 12211 and aqueous solution of Naphthenic acid salt (naphthenic acid acid value 200: 10%) 6
50S' and added it into the above reaction product at a temperature of 6
Pour at 0 to 50°C and age for 30 minutes.

The pH of the mixture will be approximately 12.

While maintaining the mixture at 60-50 DEG C. and continuing stirring, about 750 mL of an aqueous H2S04 solution (10%) is added over 60 minutes to adjust the pH to 5.7. After the pH becomes sufficiently stable, add 440 g of machine oil. Magnetite adsorbs carbibonic acid and expels water to form an oil phase! This transition will take place. Remove the water using a settling ring, wash twice with water, and then centrifuge (1
After water separation at 10,000 rpm), residual water was distilled off under reduced pressure at 165°C. The obtained ferrofluid is centrifuged.1
3000 rpm x 15 minutes), after removing the sediment,
Adjust the concentration to 45% (ash content) with 120 machine oil,
- Obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (20℃) 690 Cps Specific gravity (20℃
>1.330 Ash content (%)'' 45 Magnetizing power (60000e) 400 (G) Example 7 NaOH (granular) 692F is dissolved in water 3200. 53111CFeSO4-7H20685S' and FeCja (effective water content 39%) 16'6F-wo water 23
00 d jc Prepare a dissolved iron salt solution.

Add the iron salt solution to the NaOH solution at a reaction temperature of 27 to 40°C.
The mixture was added dropwise and stirred for 30 minutes while maintaining the temperature.

The reaction product was heated to 60°C and aged for about 30 minutes. The pH of the reaction system becomes approximately 12.

Erucic acid with salt aqueous solution (5%) 55.6. f and naphthenic acid Na salt aqueous solution (naphthenic acid acid value 200:10%) 928
f! and add this into the above reaction product at a temperature of 60~
Pour at 54°C and mature for 25 minutes. The pH of the mixture is 12
become.

Add H2SO4 aqueous solution (10%) over 60 minutes while continuing to stir the mixture to adjust the pH to 5.9. 30 motor oil 4402 is added to this after the pH is sufficiently stable. The carboxylic acid-adsorbed magnetite migrates to the oil phase.・'Water is removed using a knit ring, and after washing twice with water, water is separated by centrifugal dehydration (110,000 rP), and residual water is distilled off under reduced pressure at 135°C. The obtained magnetic fluid was centrifuged (21,0 OOy, 13000 rPm x 15 minutes),
The sediment is removed to obtain a magnetic fluid.

The physical properties of the product are as follows.

Viscosity (20℃) 1640 cps Specific gravity (2,
0°C) 1.388 Ash content (%) 45 Magnetizing power (60000e) 407 (G) Example 8 NaOH (granular) 6105' is dissolved in 2500 m/ of water.

Separately Fe2(SO4)31500Ii9MnSO4・4
~5H20289,2S” (0.55 mol) and Zn
SO4・7H2086,4F (0.2 mol) in water-1
800m/ to prepare a salt solution.

The salt solution is added dropwise to the NaOH solution and stirred for 15 to 20 minutes while maintaining the reaction temperature below 40°C. The reaction product is heated to 80°C and aged for about 10 minutes. p of the reaction system
H will be approximately 12.

Salt aqueous solution (5%) 921F and Naphthenate in erucic acid
Salt aqueous solution (naphthenic acid value 220:10%) 724fI
This was added to the above reaction product at a temperature of 80° C. and aged for 30 minutes. The pH of the mixture becomes 12.

While keeping the mixture at 55-65°C and continuing stirring, an aqueous H2SO4 solution (30%) was added over 2-3 hours to adjust the pH.
Adjust to 5.5±0.2. After the pH becomes sufficiently stable, add Lion Diffusion Pump Oil A2782 (8
0℃). The carboxylic acid adsorbed ferrite moves to the oil phase.

After removing the water with a settling ring, washing twice with water, and separating the water,
Residual moisture is distilled off under reduced pressure at 140°C. The obtained magnetic fluid is magnetically purified for 24 hours to obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (20℃) 553 cps Specific gravity (20℃
) 1.418 (Baumey meter) ash content (%)
42.5 (700'C, 30 minutes) Magnetizing force (
70400e) 597(G) Example 9 Dissolve NaOH (granular) 610F in water 256(irnl).Separately, FeSO4.7H20384f, ZnSO4
-7820139F and pecz3 (active ingredient 39
%) 1301F is dissolved in water 1840- to prepare an iron salt solution.

The iron salt solution is added dropwise to the NaOH solution and stirred for 15 to 20 minutes while maintaining the reaction temperature below 40°C. The reaction product is warmed to 50-55°C and aged for about 10 minutes. The pH of the reaction system becomes approximately 12.

Erucic acid with salt aqueous solution (5%) 1210F and naphthenic acid N
Mix 623 grams of a salt aqueous solution (naphthenic acid acid value 200:10%) and add this to the above reaction product at a temperature of 55 to 60%.
Pour in at ℃ and mature for 30 minutes. The pH of the mixture becomes 12.

The mixture was kept at 50-55°C and continuously stirred for 60 minutes to process an aqueous H2SO4 solution (30%), pH 5.5.
Adjust to ±0.2. After the pH is sufficiently stable, 65
Warm the mixture to ~70°C and add 274 g of Neothiozole (80-85°C). The carboxylic acid adsorbed ferrite migrates to the oil phase. Water is removed by settling, washed twice, and after water separation, residual water is distilled off and magnetically purified (24 hours)
to remove sediment. Next, the viscosity is adjusted to 10-20 CPS (20-C) with the above neothiozole to obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (20℃) 10~20 cps Specific gravity (2
0℃) 1.25-1.35 Ash content (%)
44-49 (700℃, 3 Gin) Magnetizing power (60
000e) 400~450(G)(1000e)
60-80 (G) Example 10 244'l of NaOH (granular) are dissolved in 10000 m/ of water. Another 4CM n SO+ 4-5 H201
A salt solution is prepared by dissolving 156,8t, Fe7sO4)36000y and ZnSO4'7H20346f in water, 7200y.

The salt solution is added dropwise to the NaOH solution and stirred for 20 to 30 minutes while maintaining the reaction temperature below 40°C. The reaction product is heated to 80°C and aged for about 10 minutes. The pH of the reaction system is approximately 12.

Erucic acid with salt aqueous solution (5%) 4486F and naphthenic acid N
A salt aqueous solution (naphthenic acid acid value 200:10%) 2314
f was mixed and added to the above reaction product at a temperature of 80°C or higher and aged for 30 minutes. The pH of the mixture will be approximately 12.

While keeping the mixture at 55-65°C and continuing stirring, an aqueous H2SO4 solution (30%) was added over 3 hours, and the pH was adjusted to -pH5,
Adjust to 5±0.2. After PTT becomes sufficiently stable, 969 grams of thiozole is added (at 70-80°C), and the carboxylic acid adsorbed ferrite is transferred to the oil phase. Water is removed by settling, washed twice with water, and after water separation, residual water is distilled off under reduced pressure. The obtained magnetic fluid is adjusted to 24 to obtain a magnetic fluid. The physical properties of the product are as follows.

Viscosity (20℃) 10~2 Q cps specific gravity (
20℃) 1.25-1.35 ash content (%)
42-48

Claims (1)

[Claims] 1. While maintaining the pH of the alkaline aqueous solution at 10 or higher,
An aqueous solution of a metal salt capable of forming a ferromagnetic substance is added to form a ferromagnetic fine particle dispersion, and an aliphatic unsaturated carbon having 18 or more carbon atoms is added in an amount to form a substantially monomolecular layer on the surface of the ferromagnetic fine particles. Mixing an acid and an aqueous salt solution of a mixed fatty acid of an alicyclic carboxylic acid having 7 or more carbon atoms, and then adjusting the pitch to 6 or less using an acid to obtain a carboxylic acid-adsorbing hydrophobic ferromagnetic fine particle dispersion, 1. A method for producing a magnetic fluid, which comprises adding a hydrophobic organic solvent thereto to transfer carboxylic acid-adsorbed hydrophobic ferromagnetic fine particles to a hydrophobic organic solvent layer.