JPS58174495A - Preparation of magnetic fluid - Google Patents

Abstract

PURPOSE:To obtain a magnetic fluid having very high dispersion stability and high magnetization ability, by mixing and dispersing fine particles of a ferromagnetic material coated with a surfactant on the surfaces thereof in an oil, ether or ester under specific conditions. CONSTITUTION:A surfactant and a low-boiling organic solvent are added to fine particles of a ferromagnetic oxide, e.g. magnetite or ferrite, having a colloidal particle diameter or fine particles of a ferromagnetic material, e.g. iron or Co alloy, to give an intermediate medium containing the fine particles, coated with the surfactant, and dispersed therein. The undispersed fine particles are then separated from the intermediate medium, and an oil, e.g. mineral oil, ester or ether is mixed therewith. The resultant mixture is then heated to evaporate the low-boiling organic solvent and afford the aimed magnetic fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses fine particles of ferromagnetic oxides, such as magnetite and ferrite, or fine particles of ferromagnetic substances, such as iron and cobalt alloys, having the size of colloidal particles. The present invention relates to a method for producing a magnetic fluid that is extremely stably dispersed in a compound or an ether, and in particular to a method for efficiently producing a magnetic fluid with high magnetization ability.

Magnetic fluid is a colloidal solution in which the above-mentioned fine particles are extremely stably dispersed in a liquid phase, so the magnetic fine particles do not aggregate or precipitate due to magnetic force, gravity, centrifugal force, etc. and separate from the liquid phase. The appearance is that the upper liquid itself has strong magnetic properties.

For this reason, in recent years, applications that take advantage of its unique properties have been developed in various fields such as sealants, damping agents, and lubricants for contact parts, and various liquids have been used as the liquid phase of O magnetic fluid. However, for applications as bearing lubricants and sealants, (1) lubricity, (2) heat resistance, (3) low volatility, and (4) chemical stability are required, so mineral oil and synthetic oil are Oils or esters or ethers such as are most suitable. In this case, the surface properties of the dispersoid need to be lipophilic in order to improve wetting of the dispersion medium.

When used as a sealant, the sealing action is performed by the magnetic fluid bound by the magnetic flux of the magnets constituting the sealing mechanism, so the stronger the magnetization of the magnetic fluid, the stronger the seal. When used as a bearing lubricant, the lubricant is a magnetic fluid bound by the magnetic force of the magnets that make up the bearing mechanism, so the stronger the magnetization of the magnetic fluid, the more capable it is of resisting the mechanical agitation force that accompanies large shaft rotations. This can create a phenomenon where the lubricant is worn out due to being splashed and the surrounding area becomes dirty. By the way, the strength of magnetization of a magnetic fluid depends on the concentration of magnetic particles contained in the fluid. Therefore, obtaining a magnetic fluid with a high concentration of magnetic particles is an extremely important issue.

However, in general, the higher the particle concentration, the smaller the distance between particles, which makes them more likely to aggregate, so a highly concentrated magnetic fluid cannot be used unless all particles have optimal dispersibility. I can't do it. If there are many large particles that tend to aggregate in the fluid or particles that do not fully absorb surfactants,
There will be a limit to the improvement of concentration.

Conventional methods for producing magnetic fluids using oils, Nisals, or ethers as a liquid phase (dispersion medium) include a method developed by Mr. Shimoizaka et al. (Unexamined Japanese Patent Publication No. 51-44579
In this conventional manufacturing method, an aqueous suspension of a colloidal ferromagnetic oxide is first obtained by a wet method. The wet method is one in which magnetite colloid is obtained by adding alkali to an acidic solution containing ferrous ions and ferric ions in a ratio of 1:2 to make the pH approximately 9 or higher, and aging at an appropriate temperature. .

In order to make the surface of the colloid particles thus obtained lipophilic, a surfactant containing unsaturated fatty acids or salts thereof as a main component is added. At this time, an excess of surfactant is added to completely coat the surface of the colloid particles, forming a two-molecule adsorbent. As is well known, monomolecular adsorption of the above-mentioned surfactant ions shows lipophilicity, but when a bimolecular layer is formed, on the contrary, it becomes a stable water-dispersed colloid with surface hydrophilicity, and solid-liquid separation is generally difficult as it is. Have difficulty. Therefore, by adjusting the concentration of the solution and rapidly coagulating and sedimenting the dispersoid, solid-liquid separation is easily achieved. Next, the precipitate is washed with a filter to remove the surfactant ions in the second molecular layer to make the particle surface lipophilic, and then dehydrated and dried. Finally, the particles are dispersed in oil to obtain the desired magnetic fluid.

This conventional two-molecular layer adsorption in aqueous solution-dispersion method in an organic phase is
Although difficult to filter hydrocolloid particles can be rapidly agglomerated by pH adjustment and treated in a short time, which is advantageous for industrialization, on the other hand, it has the following drawbacks (1) The oxide particles that become the dispersoid of the obtained magnetic fluid are
The proportion of large particles is large, and the particle size distribution is wide. Therefore, when attempting to disperse these oxide particles in a certain amount of a desired solvent, particles larger than a certain size will precipitate, making it impossible to obtain a magnetic fluid with a high S degree, that is, a high magnetizing ability.

(2) Because surfactants are added in excess to mass-produced products that are necessary to form a monomolecular layer, oily unsaturated fatty acids are created, which are adsorbed onto the particle surfaces and removed by the particles that have been incorporated into the particles. Poor fractionation.

(3) A surfactant is added to an aqueous suspension whose pH is alkaline and above the isopotential point of the colloidal particles. In this state, the surface of the colloidal particles is negatively charged, so for example unsaturated fatty acids Surfactants that have a negative charge in an aqueous solution are difficult to adsorb. Therefore, unstable particles are likely to occur in the oil.

This invention focuses on such conventional drawbacks and provides 1.:
::・1 It was made by increasing the concentration of ferromagnetic particles in particular,
It is an object of the present invention to provide a method for manufacturing a magnetic fluid that efficiently obtains a magnetic fluid with high magnetization ability.

The gist of the present invention to achieve the above object is to provide a method for producing a magnetic fluid in which fine ferromagnetic particles are dispersed in oils, esters, or ethers. A step of adding a surfactant and coating the surface of the fine particles with the surfactant, and then? :,o
A process of obtaining an intermediate medium by dispersing the reversed ferromagnetic fine particles in a low-boiling point organic solvent with a polarity close to that of desired oils, esters, or ethers, and 9 particles with poor dispersibility in this intermediate medium. After separating, desired oils or esters or ethers are added to an intermediate medium to form a mixture, and the mixture is heated to evaporate the low-boiling organic solvent. In the method of manufacturing magnetic fluid.

Hereinafter, a method for producing a magnetic fluid according to the present invention will be explained.

As the ferromagnetic fine particles of this invention, magnetite colloid obtained by the wet method described above can be used. Alternatively, it may be obtained by a so-called wet grinding method in which magnetite powder is ground in a ball mill in water or an organic solvent. Furthermore, ferromagnetic oxides other than magnetite such as manganese 7-elite, nickle aerite, cobalt ferrite, composite ferrite of these and zinc, and barium ferrite can also be used.

The process of this invention involves adding a surfactant to a suspension of ferromagnetic fine particles obtained by the above-mentioned wet method or wet pulverization method, and coating the surface of the fine particles with a surfactant molecular layer.

Surfactants include carboxyl groups (-Co.

H), hydroxy group (-OH), sulfo group (-S03H)
) and has at least one polar group such as
It may be 0 or more. This is because if the number of carbon atoms is less than 10, the fine particles will not be well dispersed. Such surface active agents include sodium salts and potassium salts of unsaturated fatty acids such as oleate ion, linoleate ion, and ψruinate ion, or N-(+,2-dicarboxyethyl)N-stearylsulfosuccinamate. When adding this surfactant, an acid is added to the suspension to adjust the pH to below the isopotential point of the colloidal particles.

When the colloid particles are iron oxide, the tip is preferably 87 or less. As a result, the surface of the colloidal particles becomes positively charged and surfactant ions are easily adsorbed.

The amount of surfactant to be added is such that it can form a monomolecular layer on the surface of the colloidal ferromagnetic fine particles, and should prevent the formation of an oily substance due to excessive addition or the formation of a hydrophilic colloid due to the formation of a bimolecular layer. It's good to do that.

When using the wet grinding method, when using something other than water as the grinding fluid, that is, an organic solvent as described below, add the desired ferromagnetic powder and an amount of surfactant that can form the monomolecular layer described above. It may be ground in a ball mill for several hours or more. In the magnetic fluid based on this organic solvent, the fractionation of the colloidal fine particles produced does not deteriorate because of the oily substance formed by 11' in excess of the surfactant.

The process of this invention involves adding an organic solvent to a suspension of fine particles that have been made hydrophobic (i.e. lipophilic) by adsorbing a monomolecular layer of surfactant ions. An intermediate medium in which ferromagnetic fine particles are dispersed in an organic solvent is obtained. Note that the stratified aqueous phase is removed by separation, but some water remaining in the organic solvent can be removed by heating and evaporation.

At this time, it is necessary to add an organic solvent to the aqueous phase suspension.
! is not necessarily the case.

After the aqueous suspension is once washed and dried to obtain hydrophobic ferromagnetic fine particles, an organic solvent may be added and dispersed.

As this organic solvent, it is desirable to have a small polarity similar to that of the desired oils, esters, or ethers described later, and a low boiling point, such as heptane, cyclohexane, toluene, hexane, pentane value, octane, etc. , paraffinic hydrocarbons such as dodecane, aromatic hydrocarbons, kerosene, etc. are used.

In the process of the present invention, fine particles with poor dispersibility in the intermediate medium are removed by centrifugation at, for example, 5,000 to 8,000 G, and then desired oils, esters, or ethers are added and sufficiently stirred to form a mixture. It is something.

In the state of the intermediate medium, ferromagnetic fine particles are sorted into those with good dispersibility and those with poor dispersibility. The first sorting is performed when dispersing in an organic solvent, and the second sorting is carried out, and further sorting is carried out using centrifugal force.

By repeating the sorting in this way, the concentration of ferromagnetic fine particles in the intermediate medium will decrease rapidly, but since the intermediate medium can be easily volatilized, the desired oils, esters, or ethers can be removed. By adding <D, a large amount of ferromagnetic fine particles can be dispersed in the magnetic fluid.

If desired oils, esters, or ethers are directly added without using such an intermediate medium, it is difficult to distill and concentrate them by heating, since low volatility is required for the intended use. It is.

Furthermore, even if you try to increase the content of ferromagnetic particles by initially adjusting the amount of oil, ester, or ether solution to a small amount, the dispersibility of the ferromagnetic particles will always be poor. The content of ferromagnetic fine particles with good dispersibility is therefore limited and is originally small.

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.

Mineral oil or synthetic oil is used as the oil, but it is important to select the organic solvent and the oil, ester, or ether that are similar in polarity to some extent.

Along with this oil or ester or ether, the second
A surfactant may also be added. As the second surfactant, use is made of a nonionic surfactant that is soluble in the desired oil and whose day LB is within 5 of the solubility limit in the desired oil, such as polyoxyethylene nonylphenol ether with various HLBs. . This second surfactant does not necessarily need to be added, but if some of the ferromagnetic particles do not have sufficient adsorption of the first surfactant, the nonionic surfactant may be present on the surface of the particles. 1. Other nonionic surfactants include ethers, alkylphenols, esters, sorbitan esters, and polyhydric alcohols. However, mixtures of these can also be used.

The process of the present invention is based on a book in which the mixture obtained as described above is heated in the air or in a vacuum to evaporate the organic solvent with a low boiling point. During this evaporation process, +! was dispersed in the organic solvent phase! ! The magnetic fine particles migrate into the oil, esters, or ethers, and finally a magnetic fluid having the desired oil, ester, or ether as a liquid phase is obtained.

Since the polarities of oils, esters, or ethers and the organic solvent are relatively close, the transfer of magnetic particles due to evaporation occurs naturally and smoothly. Stable dispersion can be maintained even when the concentration of dispersed particles is high.

The magnetic fluid using the oil, ester, or ether thus obtained as a medium is further added to
After centrifugation at
By repeating the steps of mixing again and evaporating the low-boiling organic solvent from this mixture, highly dispersible fine particles can be further added, and a magnetic fluid with an extremely high concentration of fine particles can be obtained.

According to this invention, after the ferromagnetic fine particles are made lipophilic, they are first made into an intermediate medium using a low boiling point organic solvent, and then desired oils, esters, or ethers having similar polarity are added thereto. By distilling the resulting mixture, low-boiling seafood is removed and concentrated, making it possible to efficiently and economically produce highly concentrated magnetic fluids using oils, esters, or ethers as a medium. . Therefore, it becomes possible to provide high-performance bearing lubricants and sealants at low cost.

The present invention will be explained in detail below.

Example (1) Preparation of a magnetic fluid using polybutene (8-stone LV-25E) as a solvent and magnetite as a dispersoid First, add 6N NaOH to an aqueous solution 11 of 1 mol/e each of ferrous sulfate and ferric sulfate.
After adding an aqueous solution until the pH became 11 or higher, the mixture was aged at 60° C. for 30 minutes to obtain a magnetite colloid. Then, add 3N to the magnetite suspension while keeping it at 60℃.
Add HCl solution to pH between 4 and 5! After adjusting the temperature, 20 g of sodium oleate is added and stirred for 30 minutes. After standing still and agglomerating the magnetite particles,
The electrolyte is removed by discarding the supernatant, adding water, and discarding the water. Repeat this process several times to remove the electrolyte.

At this time, when the pH rises and the mixture becomes dispersed, a smaller amount of HCl is added. Then, transfer this liquid to a separatory funnel, add hexane, stir thoroughly, and let stand to separate water and hexane. 8 hexane in which magnetite is dispersed
Centrifugation was performed for 20 minutes under a centrifugal force of 000G. Take the upper supernatant liquid, add 30 cc of polybutene and the nonionic surfactant polyoxyethylenenonylphenol ether (HL).
Add IOC of B 7+5) and mix. The mixture was maintained at 90° C. and the organic solvent was evaporated using a rotary evaporator. After evaporation, magnetite is dispersed in polybutene. This is separated under centrifugation at 8000G for 60 minutes. This operation removed the undispersed solids, but the colloidal solution above was a very stable magnetic fluid.

Example (2) Dioctylazibe) (Ca Ha (COOC88
17) Preparation of magnetic fluid using 2] as a solvent and magnetite as a dispersoid The method for preparing magnetite and the method for dispersing it in hexane are the same as in Example (1).

The hexane solution separated in the separating funnel was centrifuged for 20 minutes under a centrifugal force of 8000G. The upper supernatant liquid is removed and the hexane is evaporated using a constant temperature dryer to dry the magnetite particles.

After drying, take 5 g of magnetite particles, add 25 cc of dioctylazibe and the nonionic surfactant polyoxyethylenenonylphenol ether (HLB).

Add 5 cc of 12.8) and mix. After mixing, the mixture was reheated in vacuum to completely remove the water in the oil and the water adsorbed on the magnetite.

After cooling, separate under centrifugation at 8000G for 60 minutes.

Although non-dispersed solids were removed by this operation, the Colloid 1 solution above was an extremely stable magnetic fluid.

Procedural amendment October 14, 1982 [( Commissioner of the Patent Office Kazuo Wakasugi 1, 1+, indication of the matter 1981 Patent Application No. 566
No. 54 No. 2, Title of invention: Method for manufacturing magnetic fluid 3, Relationship with the young case to be supplemented Applicant's address ##: 2-3-2-6 Marunouchi, Chiyoda-ku, Tokyo Number of inventions increased by amendment 7, Subject of amendment: Specification, Nei Kiyoshi (detailed explanation of the invention) 8, Contents of hli iE Attachment 3, 84 Contents of amendment (1) “O” in line 10, page 10 of the specification is corrected to "to".

(2) In the same book, 12th negative line 5, ``It is something to be gained.

Furthermore, "stratification" will be corrected as follows.

Alternatively, a low boiling point organic solvent may be added to the ferromagnetic fine particles to form a suspension, and then a surfactant may be added to obtain an intermediate medium, or a surfactant and a low boiling point organic solvent may be added to form a suspension. You may also obtain an intermediate medium by adding a mixture of
Then add j to the desired oil or ether or ester.
and correct it.

(4) Correct 1 for the desired oil in the second line of the same page of the same circular to ``j for the desired oil, ether, or ester. can."
You can get r. In the above description, the method for manufacturing a magnetic fluid using ferromagnetic particles obtained by a wet method may be used, but ferromagnetic particles obtained by a dry method may also be used. ” he corrected.

Claims (1)

[Claims] (1) A method for producing a magnetic fluid in which fine ferromagnetic particles are dispersed in a desired oil, ester, or ether, wherein the fine ferromagnetic particles are combined with a surfactant and a low-boiling organic solvent. A step of obtaining an intermediate medium in which ferromagnetic fine particles whose surfaces are coated with a surfactant are dispersed under medium pressure in a low boiling point organic solvent, and after separating fine particles with poor dispersibility in the intermediate medium, the desired A step of adding oils or esters or ethers to an intermediate medium to form a mixture, heating the mixture,
A method for producing a magnetic fluid, comprising the step of evaporating a low boiling point organic solvent. (2) In a method for producing a magnetic fluid in which fine ferromagnetic particles are dispersed in desired oils, esters, or ethers, a surfactant and a low-boiling organic solvent are added to the fine ferromagnetic particles, and the surface A process of obtaining an intermediate medium in which ferromagnetic fine particles coated with an activator are dispersed in a low-boiling organic solvent under medium pressure. After separating fine particles with poor dispersibility in the nuclear intermediate medium, the intermediate medium is heated and a low-boiling organic solvent is dispersed. evaporating the solvent;
A method for producing a magnetic fluid, comprising the step of adding desired oils, esters, or ethers to the ferromagnetic fine particles that have undergone this step. (3) A patent claim in which a surfactant is added to ferromagnetic fine particles to coat the surface of the ferromagnetic fine particles with the surfactant, and a low boiling point organic solvent is added to the coated ferromagnetic fine particles to obtain an intermediate medium. A method for producing a magnetic fluid according to scope 1 or 2. (4) The magnetic fluid according to claim 1 or 2, in which a low boiling point organic solvent is added to ferromagnetic fine particles to form a suspension, and a surfactant is added to the suspension to obtain an intermediate medium. (5) A method for producing a magnetic fluid according to claim 1 or 2, wherein an intermediate medium is obtained by adding a mixture of a surfactant and a low-boiling organic solvent to ferromagnetic fine particles. +61 surfactant tiCOOH group, OH group, 5Ch
Claim IPJ1 is at least one of acids having one or more polar groups such as H groups and 10 or more carbon atoms, or lactones, salts, or esters thereof.
6. A method for producing a magnetic fluid according to any one of items 5 to 6. (7) When coating ferromagnetic fine particles in an aqueous suspension, the surfactant is added in an amount sufficient to form a monomolecular layer on the surface of the ferromagnetic fine particles. 6. A method for producing a magnetic fluid according to any one of Item 6. (8) The pH of an aqueous suspension of ferromagnetic fine particles is adjusted to below the equipotential point of the ferromagnetic fine particles, and a surfactant is added to the aqueous suspension. A method for producing a magnetic fluid according to any one of the above. (9) The method for producing a magnetic fluid according to any one of claims 1 to 8, wherein a nonionic surfactant is added to the desired oils, esters, or ethers. Particularly, after producing a magnetic body using desired oils, esters, or ethers as a solvent, fine particles with poor dispersibility are removed, and then the magnetic fluid is added to an intermediate medium to form a mixture. A method for producing a magnetic fluid according to item 1.