JPS63124402A - Fluorine-based magnetic fluid composition and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a fluorine based magnetic fluid composition material which has high dispersion stability by dispersing ferromagnetic particles in a perfluorinated solvent with a specific surface active agent. CONSTITUTION:Ferromagnetic particles are stably dispersed in a perfluorinated solvent with a perfluoropolyether derivative shown by the formula or at least one sort of the salts. R is, however, a polar group selected from groups -COOH, -CH2OH, -OH, -SO3OH, PO3H, HN2, etc. The particle size of the ferromagnetic material is 20-500 Angstrom and the content is within 1-30 % in volume ratio. An intermediate medium wherein the ferromagnetic material wherein the ferromagnetic particles are added with the above mentioned surface- active agent and the perfluorinated solvent of low boiling point and the surface is coated with the surface-active agent is dispersed in the solvent is manufactured. After the particles which are not well dispersed in the intermediate medium are separated, a stable magnetic particle colloid solution is made by adding a dispersant after evaporating the low boiling point solvent by adding a solvent and by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic fluid composition in which fine ferromagnetic particles are stably dispersed in a fluorine-based solvent, and a method for producing the same.

[Conventional technology]

Magnetic fluids include magnetite, ferrite, and iron.

It is an extremely stable colloidal solution in which fine particles of ferromagnetic material such as cobalt are dispersed in a liquid, and the liquid itself has the property of apparently exhibiting strong magnetism. Therefore, although it is a liquid, its behavior can be restrained freely by magnets, etc., so it has a wide range of applications, including as a damping agent and a sealing agent in sealing mechanisms for magnetic disks and the like.

The specifications and performance required vary depending on the field of application, including low torque, cold resistance, chemical resistance, and insulation, as well as compatibility with water and hydrocarbon oils. There are cases where it is required not to have one.

Such demands cannot be met with conventional magnetic fluids using general hydrocarbon solvents as dispersion media. Therefore, a method using a perfluorinated solvent as a dispersion medium has been proposed (US Pat. No. 3,784,471). This uses a perfluoro-based solvent as a dispersion medium and uses a fluorocarbon-based surfactant to stably disperse ferromagnetic fine particles in the dispersion medium. That is, the dispersion medium is a perfluoropolyether represented by the general formula (A in the formula is a fluorine atom or a hydrogen atom), whereas the dispersion stabilizer for ferromagnetic fine particles is, for example, a fluorocarbon represented by the formula A type of surfactant is used.

[Problem that the invention seeks to solve]

However, the conventional fluorocarbon surfactant represented by the above general formula is replaced by perfluoropolyether oil F3 ■ CF3 [(OCF CFZ)ll (OCF
2)-]OCF3, (n:m=40:
When used for 1), there was a problem in that the two structures were different, so the affinity decreased and the dispersion of the ferromagnetic fine particles became unstable.

This invention was made by focusing on such conventional problems, and uses perfluoropolyether oil represented by the structural formula %:1) as a dispersion medium,
A fluorinated magnetic fluid with high dispersion stability is used as a surfactant for dispersing the ferromagnetic fine particles by using a perfluoropolyether derivative with the same perfluoropolyether structure. The object of the present invention is to provide a composition and a method for producing the same.

[Means for solving problems]

The composition of the present invention is a fluorinated magnetic fluid composition in which fine ferromagnetic particles are stably dispersed in a perfluorinated solvent via a surfactant, wherein the surfactant has the general formula %. ) (R in the formula is COOH, CHz OH.

OH, S Os OH, P Os H.

A fluorine-based magnetic fluid composition characterized in that it is at least one of the perfluoropolyether derivatives or salts thereof represented by the following formula (a polar group selected from the group of -NH2, etc.).

Further, the manufacturing method of the present invention includes adding a surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluoro-based low boiling point solvent to ferromagnetic fine particles, and producing a ferromagnetic material whose surface is coated with the surfactant. a step of obtaining an intermediate medium in which fine particles are dispersed in a low-boiling point solvent; a step of separating fine particles with poor dispersibility in the intermediate medium and then adding a perfluoro solvent to the intermediate medium to form a mixture; The method for producing a fluorine-based magnetic fluid composition includes the step of heating and evaporating the low boiling point solvent.

Furthermore, another manufacturing method of the present invention includes adding a surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluoro-based low boiling point solvent to ferromagnetic fine particles,
A step of obtaining an intermediate medium in which ferromagnetic fine particles whose surface is coated with the surfactant is dispersed in a low boiling point solvent, and after separating fine particles with poor dispersibility in the intermediate medium, heating the intermediate medium and dispersing the low boiling point solvent. This is a method for producing a fluorine-based magnetic fluid composition, which includes a step of evaporating a boiling point solvent and a step of adding a perfluoro-based solvent to the ferromagnetic fine particles that have undergone the step.

Specifically, the manufacturing method of the present invention includes adding a surfactant made of a perfluoropolyether derivative or a salt thereof to ferromagnetic fine particles, and coating the surface of the ferromagnetic fine particles with the surfactant. , is a method for producing a fluorine-based magnetic fluid composition, in which an intermediate medium is obtained by adding a perfluorinated low-boiling point solvent to the coated ferromagnetic fine particles.

In addition, a perfluorinated low-boiling point solvent is added to ferromagnetic fine particles to form a suspension, and a surfactant consisting of a perfluoropolyether derivative or a salt thereof is added to the suspension to obtain an intermediate medium. A method for producing a fluid composition.

In addition, there is a method for producing a fluorinated magnetic fluid composition in which an intermediate medium is obtained by adding a mixture of a surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluorinated low-boiling solvent to ferromagnetic fine particles. .

Another method is to produce a fluorinated magnetic fluid composition in which a surfactant made of a perfluoropolyether derivative or a salt thereof is added in an amount sufficient to form a monomolecular layer on the surface of the ferromagnetic fine particles.

In addition, a fluorine-based magnetic fluid composition is produced by producing a magnetic fluid using a desired perfluorinated solvent as a dispersion medium, removing fine particles with poor dispersibility, and then adding the magnetic fluid to an intermediate medium to form a mixture. It's a method.

[Effect]

The perfluoropolyether oil used as a dispersant for the magnetic fluid of this invention has excellent lubricating properties, is sufficiently inert and nonvolatile, and has excellent vacuum properties, so it can be used as a lubricant and sealing material for aerospace applications. It is suitably used. Therefore, by using this as a dispersion medium and a perfluoropolyether derivative or a salt thereof having the same structure of the perfluoropolyether moiety as a surfactant for dispersing the ferromagnetic fine particles in the dispersion medium, it is possible to A fluorine-based magnetic fluid that has low vapor pressure, good lubrication properties, and extremely excellent dispersion stability can be obtained, making it ideal for aerospace sealants and the like.

Hereinafter, the fluorine-based magnetic fluid composition of the present invention and its manufacturing method will be explained in detail.

The perfluorinated solvent used as a dispersion medium for the magnetic fluid of this invention is a perfluoropolyether oil having an extremely low vapor pressure and excellent lubricating properties, and its structural formula is F 3 CF 3 [(OCF CFz)-( OCF2)TI]
-〇-CF3, (n:m=40:1)
It is indicated by.

As the ferromagnetic fine particles of this invention, magnetite colloid obtained by a wet method can be used.

The wet method here means that ferrous ions and ferric ions are
A magnetite colloid is obtained by adding an alkali to an acidic solution containing a ratio of 1:2 to 1:2 to adjust the pH to about 9 or more, and aging at an appropriate temperature. Alternatively, it may be obtained by a so-called wet pulverization method in which magnetite powder is pulverized in water or a solvent using a ball mill.

When using the wet grinding method, when using an organic solvent such as hexane outside the water as the grinding fluid, add ferromagnetic powder and an amount of surfactant that can form a monomolecular layer on the particle surface. It may be ground in a ball mill for several hours or more.

Also, manganese ferrite other than magnetite.

Ferromagnetic oxides such as cobalt ferrite or composite ferrites of these with zinc and nickel, barium ferrite, or ferromagnetic metals such as iron and cobalt-6 rare earths can also be used.

Furthermore, as the ferromagnetic fine particles, in addition to those obtained by the above-mentioned wet method or wet pulverization method, those obtained by a dry method can also be used.

The particle size of the ferromagnetic fine particles of this invention is between 20 and 500. For example, magnetite has an inverted spinel structure with a unit cell having a lattice constant of about 8 people, and since a crystal consists of several or more unit cells, a particle size of at least 20 Å is required. On the other hand, regarding the upper limit of the particle size, from the viewpoint of the stability of the magnetic fluid as a suspension of magnetic particles, λ=
The parameter λΦ value expressed as MS"y2/d'kT is important. (where MS: saturation magnetization, V2 particle volume, d: particle diameter, and N: Bolsomann's constant.

T: absolute temperature). Generally, the limit value at which agglomeration can be prevented by resisting interparticle attraction and magnetic dipole attraction of magnetic particles by the repulsive force of a surfactant layer adsorbed and formed on the particle surface is set to λ-10''. Therefore, we now estimate the safety λ−
10'' and saturation magnetization MS = 400G, the upper limit of the particle diameter d determined by the above formula is 500.However, the desirable particle size is around 100.In this case, in the above formula, When M s = 400 G, it becomes λ-1, and there is no fear that the dispersed magnetic fine particles will settle even if they are left standing for a long time.

The content of the ferromagnetic fine particles of the present invention is of course in the conventionally generally used range of 1 to 20% by volume;
If necessary, the concentration may be as high as about 30%. That is, according to the present invention, the concentration of ferromagnetic particles can be adjusted to a high concentration of up to 30% by using an intermediate medium in which ferromagnetic particles are dispersed in a low boiling point solvent, as described later. can. This makes it possible to obtain a magnetic fluid with extremely high magnetization.

The additive for stably dispersing the ferromagnetic fine particles in the solvent of perfluoropolyether oil in this invention is a perfluoropolyether derivative represented by the general formula (%), where R is , -CO○H, CH20H, OH.

It is a derivative having a polar group selected from the group of S 2 O, 1OH, P 3 O3H, N 2 Hz, etc., or a salt thereof, and at least one of them is selected and used.

The method for producing the fluorine-based magnetic fluid composition of the present invention includes:
First, ferromagnetic fine particles and a surfactant are added to a low boiling point perfluorinated solvent to obtain an intermediate medium in which ferromagnetic fine particles whose surfaces are coated with a surfactant are dispersed in the low boiling point lighting medium. It is. Next, fine particles with poor dispersibility in the intermediate medium are removed by centrifugation at, for example, 5,000 to 8,000 G. Then, perfluoropolyether oil as a dispersion medium is added and mixed, and the mixture is then heated to evaporate the low-boiling perfluorinated solvent, or alternatively, the intermediate medium is heated to remove the low-boiling perfluorinated solvent. By adding a dispersion medium to the magnetic fluid particles after evaporating the solvent, a highly concentrated and extremely stable magnetic particle colloidal solution is obtained.

In the state of the intermediate medium, the ferromagnetic fine particles are sorted into those with good dispersibility and those with poor dispersibility. If this sorting is repeated, the concentration of ferromagnetic fine particles in the intermediate medium will decrease considerably, but since the intermediate medium can be easily evaporated and concentrated, another new intermediate medium is added to the concentrated medium, and this Further, by repeating the concentration and mixing with perfluoropolyether oil as a dispersion medium, it becomes possible to disperse a large amount of ferromagnetic fine particles in the magnetic fluid.

If a dispersion medium is directly added without using such an intermediate medium, since the dispersion medium has low volatility, it is difficult to distill and concentrate by heating, and it is difficult to obtain a concentration at a constant yield.

In addition, even if you initially try to increase the content of ferromagnetic particles by adjusting the amount of dispersion medium to a small amount, ferromagnetic particles whose dispersibility is not very good will always be taken into the solution once. The content of ferromagnetic fine particles with good dispersibility is limited. Moreover, these ferromagnetic particles with insufficient dispersibility not only separate and settle themselves during centrifugation, but also settle together with the ferromagnetic particles with good dispersibility that were floating adjacent to them. As a result, a large amount of precipitate is generated and the number of ferromagnetic particles in the solution is significantly reduced, making it difficult to obtain the concentration of ferromagnetic particles required for performance.

However, in order to obtain the fluorine thread-based magnetic fluid composition of the present invention, it is not necessarily necessary to use the above-mentioned intermediate medium. It may be mixed with.

Examples of the fluorine-based magnetic fluid composition of the present invention will be described below along with the manufacturing process thereof.

[Example 1] First, a 6N NaOH aqueous solution was added to 300 - of 1 mol/l aqueous solutions of ferrous sulfate and ferric sulfate to adjust the pH to 1.
1 or more, and then aged at 60°C for 30 minutes to obtain magnetite colloid. Thereafter, 3N HCl was added to this magnetite slurry while maintaining the temperature at 60°C to adjust the pH to 5. Perfluoropolyether carboxylic acid (manufactured by Montefluos, GARDEN monoacta) represented by the following structural formula was used as a surfactant to stably disperse colloidal particles in this magnetite slurry.
Add 40g and stir for 30 minutes.

Fj CFa [(OCF CFz)fi (OCFz)
m] OCFt C0OH When this is allowed to stand still and the magnetite particles aggregate and settle,
Discard the supernatant, pour in water, and repeat the process of rinsing with water several times to remove the electrolyte. After washing with water, filter and dehydrate. Perfluorocarbon with a boiling point of 97°C (manufactured by Jujutsu 3M Co., Ltd., FC-7) was added to the obtained magnetite particles.
7) as a low boiling point solvent and shake thoroughly to disperse the magnetite particles. As a result, an intermediate medium is obtained in which fine ferromagnetic particles whose surfaces are coated with a surfactant are dispersed in a low boiling point solvent. Next, this intermediate medium liquid was heated to 8000G
Centrifuge for 1 hour at a centrifugal force of . After large magnetite particles are separated by sedimentation, the supernatant is taken out and filtered, and the filtrate is collected in a rotary evaporator and kept at 90°C to evaporate low-boiling perfluorocarbon and water. After evaporation, take 5 g of magnetite particles remaining in the evaporator flask, add the above low boiling point perfluorocarbon again to redisperse the magnetite particles, and then add perfluoropolyether synthetic oil (M
Manufactured by ONTEFLUO3, FOMBLIN: YO6/6
) and mix well.

This mixture was collected in a rotary evaporator and
When the low boiling point perfluorocarbon is evaporated while maintaining the temperature at C, the magnetite particles are dispersed in the perfluoropolyether synthetic oil. By centrifuging this at 8000 G centrifugal force for 30 minutes, undispersed solids were removed, but the colloidal solution above was an extremely stable magnetic fluid.

[Example 2] First, a 6N NaOH aqueous solution was added to 300-1 mol/Il aqueous solution of ferrous sulfate and ferric sulfate to adjust the pH to 11.
After the above-mentioned conditions, the mixture was aged at 60°C for 30 minutes to obtain an aqueous solution of colloid on a magnetite. Leave this to stand, and when the magnetite particles aggregate and settle, discard the supernatant and pour in water.
Further, the electrolyte is removed by repeating the water washing operation several times. After washing with water, it was filtered, dehydrated, and then vacuum-dried at 80°C for 5 hours. The obtained magnetite particles were mixed with a low boiling point perfluorocarbon solvent (manufactured by Jujutsu 3M, FC-77, boiling point 97°C) and perfluoropolyether carboxylic acid (M, 0NTEF) as a surfactant.
Manufactured by LUO3, GARDEN monoactd) 1
6 g was added and mixed by pulverization in a ball mill for 2 hours. This mixture was collected in a rotary evaporator and kept at 90°C to evaporate the low boiling point perfluorocarbon. 2g of magnetite particles remaining in the evaporator flask after evaporation
After adding the above-mentioned low boiling point perfluorocarbon again to redisperse the magnetite particles, perfluoropolyether synthetic oil (MONTF, manufactured by FLOUS Co., Ltd.,
Add 2.5 g of FOMBLIN:Y○6/6) and mix well. This mixture is collected in a rotary evaporator and kept at 90°C to evaporate and remove the low boiling point perfluorocarbon solvent, and the magnetite particles are dispersed in the perfluoropolyether synthetic oil. By centrifuging this at 8000 G centrifugal force for 30 minutes, non-dispersed solids were removed, but the colloidal solution above was an extremely stable magnetic fluid.

〔Effect of the invention〕

According to this invention, ferromagnetic fine particles are dispersed in a perfluoropolyether solvent via a surfactant made of a perfluoropolyether derivative, resulting in low vapor pressure, good lubricating properties, and extremely This has the effect that a fluorine-based magnetic fluid composition having excellent dispersion stability can be obtained.

In addition, in the production method of the present invention, fine particles with poor dispersibility are selected and removed via an intermediate medium in which ferromagnetic fine particles whose surfaces are coated with a surfactant are dispersed in a low-boiling perfluorinated solvent, and then, Since the low boiling point solvent is removed by evaporation, it is possible to easily and inexpensively provide a highly concentrated and extremely stable fluorine-based magnetic fluid composition.

Claims (16)

[Claims] (1) In a fluorine-based magnetic fluid composition in which ferromagnetic fine particles are stably dispersed in a perfluorinated solvent via a surfactant, the surfactant has a general formula ▲ mathematical formula, chemical formula, table, etc. ▼ (R in the formula is -COOH, -CH_2OH, -OH,
-SO_3OH, -PO_3H, -NH_2, etc.) A fluorinated magnetic fluid composition characterized in that it is at least one of perfluoropolyether derivatives or salts thereof. . (2) The fluorine-based magnetic fluid composition according to claim 1, wherein the ferromagnetic fine particles have a particle size of 20 to 500 Å. (3) The fluorinated magnetic fluid composition according to claim 1 or 2, wherein ferromagnetic fine particles are dispersed in the perfluorinated solvent in a volume ratio of 1 to 30%. (4) Perfluorinated solvents have general formulas ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (n:m=40:1
) The fluorine-based magnetic fluid composition according to any one of claims 1 to 3, which is a perfluoropolyether oil represented by: (5) A surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluoro-based low boiling point solvent are added to ferromagnetic fine particles, and the ferromagnetic fine particles whose surfaces are coated with the surfactant are used as a low boiling point solvent. a step of obtaining an intermediate medium dispersed in the intermediate medium, a step of adding a perfluoro solvent to the intermediate medium to form a mixture after separating fine particles with poor dispersibility in the intermediate medium, and heating the mixture to form a mixture. and evaporating a low boiling point solvent. (6) A surfactant made of a perfluoropolyether derivative or a salt thereof is added to the ferromagnetic fine particles to coat the surface of the ferromagnetic fine particles with the surfactant, and the coated ferromagnetic fine particles are coated with perfluorinated fine particles. 6. The method for producing a fluorine-based magnetic fluid composition according to claim 5, wherein an intermediate medium is obtained by adding a low-boiling point solvent. (7) A patent claim for obtaining an intermediate medium by adding a perfluorinated low-boiling point solvent to ferromagnetic fine particles to form a suspension, and adding a surfactant made of a perfluoropolyether derivative or a salt thereof to the suspension. A method for producing a fluorine-based magnetic fluid composition according to item 5. (8) Fluorine according to claim 5, in which an intermediate medium is obtained by adding a mixture of a surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluorinated low-boiling solvent to ferromagnetic fine particles. A method for producing a based magnetic fluid composition. (9) A magnetic fluid is produced using a desired perfluorinated solvent as a dispersion medium, fine particles with poor dispersibility are removed, and the magnetic fluid is then added to an intermediate medium to form a mixture. A method of manufacturing the fluorinated magnetic fluid composition described above. (10) A surfactant consisting of a perfluoropolyether derivative or a salt thereof is added in an amount sufficient to form a monomolecular layer on the surface of the ferromagnetic fine particles. A method for producing a fluorine-based magnetic fluid composition according to claim 1. (11) A surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluoro-based low boiling point solvent are added to ferromagnetic fine particles, and the ferromagnetic fine particles whose surface is coated with the surfactant are used as a low boiling point solvent. a step of separating poorly dispersible fine particles in the intermediate medium and then heating the intermediate medium to evaporate the low boiling point solvent; and adding a perfluorinated solvent. (12) A surfactant made of a perfluoropolyether derivative or a salt thereof is added to the ferromagnetic fine particles to coat the surface of the ferromagnetic fine particles with the surfactant, and the coated ferromagnetic fine particles are coated with perfluoropolyether. 12. The method for producing a fluorine-based magnetic fluid composition according to claim 11, wherein an intermediate medium is obtained by adding a low-boiling point solvent. (13) A patent claim for obtaining an intermediate medium by adding a perfluorinated low-boiling point solvent to ferromagnetic fine particles to form a suspension, and adding a surfactant made of a perfluoropolyether derivative or a salt thereof to the suspension. A method for producing a fluorine-based magnetic fluid composition according to item 11. (14) Fluorine according to claim 11, in which an intermediate medium is obtained by adding a mixture of a surfactant made of a perfluoropolyether derivative or a salt thereof and a perfluorinated low-boiling solvent to ferromagnetic fine particles. A method for producing a based magnetic fluid composition. (15) Claim 11, in which a magnetic fluid is produced using a desired perfluorinated solvent as a dispersion medium, fine particles with poor dispersibility are removed, and then the magnetic fluid is added to an intermediate medium to form a mixture. A method of manufacturing the fluorinated magnetic fluid composition described above. (16) A surfactant consisting of a perfluoropolyether derivative or a salt thereof is added in an amount sufficient to form a monomolecular layer on the surface of the ferromagnetic fine particles. A method for producing a fluorine-based magnetic fluid composition according to claim 1.