JPS63140505A - Magnetic fluid composition and manufacture of the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic fluid composition in which fine particles of ferromagnetic material are extremely stably dispersed in a dispersion medium and a method for producing the same, and is particularly applicable to vacuum seals, etc. The present invention relates to a suitable low vapor pressure, low viscosity magnetic fluid composition and a method for producing the same.

[Prior Art] A magnetic fluid is an extremely stable colloidal solution of fine ferromagnetic particles, and the liquid itself has the property of apparently exhibiting strong magnetism.

When this is used as a sealant, the sealing action is performed by the magnetic fluid bound by the magnetic flux of the magnets that constitute the sealing mechanism. Therefore, the stronger the magnetization of the magnetic fluid, the stronger the seal. By the way, the strength of magnetization of magnetic fluid is
Obtaining a magnetic fluid with a high concentration of magnetic particles is an extremely important issue because it depends on the concentration of magnetic particles contained in the fluid. However, in general, the higher the particle concentration is, the smaller the particle spacing becomes, making it easier for particles to agglomerate.

Therefore, a highly concentrated magnetic fluid cannot be obtained unless all particles have optimal dispersibility. Furthermore, if there are many large particles that tend to aggregate in the fluid or particles that do not completely adsorb the surfactant, there will be a limit to the improvement of the concentration.

The present applicant has focused on this point and previously proposed a magnetic fluid composition having a high magnetic particle concentration and a method for producing the same (Japanese Patent Laid-Open No. 105093/1983). This has a carbon number of 25 to 4
This is a magnetic fluid composition in which ferromagnetic particles coated with a surfactant are dispersed in a dispersion medium containing polyalphaolefin oil containing oligomer No. 5 as a main component.

In order to obtain a highly concentrated and stable magnetic particle composition, we first created an intermediate medium in which ferromagnetic particles were dispersed in a low-boiling organic solvent, and then separated fine particles with poor dispersibility in the intermediate medium. Thereafter, the low boiling point organic solvent is heated and evaporated, so that the ferromagnetic particles are dispersed in a concentrated state in polyalphaolefin oil as a dispersion medium.

[Problem that the invention seeks to solve]

The conventional magnetic fluid using polyalphaolefin oil as a dispersion medium has low volatility and lower viscosity than magnetic fluid using mineral oil as a dispersion medium, which has a similar evaporation rate. However, it is still unsuitable for use as a sealant in fields that require even lower volatility, thermal stability, and low hygroscopicity, such as in the field of vacuum technology.

This invention was made by focusing on these conventional problems, and has developed a magnetic fluid that has low viscosity, extremely low vapor pressure and hygroscopicity, and high thermal stability, making it ideal as a vacuum sealant. The present invention aims to provide a composition and a method for producing the same.

[Means for solving problems]

The composition of the present invention is a magnetic fluid composition comprising fine ferromagnetic particles adsorbed with a surfactant dispersed in a dispersion medium consisting of an organic solution, wherein the dispersion medium is alkylnaphthalenes or alkyl polyphenyl ethers. A magnetic fluid composition comprising at least one of the following.

Further, in the first manufacturing method of the present invention, a surfactant and a low-boiling organic solvent are added to the ferromagnetic fine particles, and the ferromagnetic fine particles whose surfaces are coated with the surfactant are dispersed in the low-boiling organic solvent. a step of separating fine particles with poor dispersibility in the intermediate medium, and then adding at least one of alkylnaphthalenes or alkyl polyphenyl ethers to the intermediate medium to form a mixture; and heating the mixture to evaporate the low boiling point organic solvent.

Furthermore, a second manufacturing method of the present invention includes adding a surfactant and a low-boiling organic solvent to the ferromagnetic fine particles, and dispersing the ferromagnetic fine particles whose surfaces are coated with the surfactant in the low-boiling organic 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 organic solvent; adding at least one of naphthalenes or alkyl polyphenyl ethers.

(Function) The alkylnaphthalenes and alkyl polyphenyl ethers used as the dispersion medium of this invention are stable oils with extremely low vapor pressure that are also used as vacuum pump oil for diffusion pumps that create ultra-high vacuums. By using this as a dispersion medium, it is possible to obtain a magnetic fluid that has low vapor pressure, low viscosity, low pour point, and excellent thermal and oxidative stability, making it ideal for high-vacuum sealants.

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

The dispersion medium of ferromagnetic particles of this invention has a vapor pressure of 1
It is desirable that the viscosity is extremely low and viscosity is as low as 10-'torr or less, and alkyl polyphenyl ethers
Dialkyl polyphenyl ethers are preferred. For example, hexadecyl diphenyl ether (vapor pressure: 5X1
0-”torr).

Octadecyl diphenyl ether (IXIO-”tor
r), hexadecyl triphenyl ether (IXIO-
9 torr), hexadecyltetraphenyl ether (
IXIO-''torr), dihexadecyltetraphenyl ether (IXIO-''torr), and the like.

These alkyl polyphenyl ether oils have the characteristics of low vapor pressure and low viscosity by adding an alkyl group to polyphenyl ether, which has been conventionally used as ultra-high vacuum oil. By the way, tetraphenyl ether, which belongs to polyphenyl ether, has a vapor pressure of 3X10-9 torr and a viscosity of 120 cSt.
(a t40°C, same below). On the other hand, octadecyl diphenyl ether and hexadecyl triphenyl ether, which belong to the alkyl polyphenyl ethers, have similar low vapor pressures (above) and viscosity of 25 cSt and 60 C5L, respectively, which are 115 to 1/2
It's nothing more than that.

As other low vapor pressure and low viscosity dispersion media, alkylnaphthalenes used as diffusion pumps for ultra-high vacuums can also be suitably used. However, in order to expect a vapor pressure similar to that of polyphenyl ether,
The number of carbon atoms in the alkyl chain is preferably 20 or more, such as eicosylnaphthalene (vapor pressure: 5XI Q-'t
o r r, viscosity: 38 cSt).

Any of the above alkylnaphthalenes or alkyl polyphenyl ethers may be used alone or in combination.

As the ferromagnetic fine particles of the present invention, magnetite colloids obtained by a well-known wet method can be used. Alternatively, it may be obtained by a so-called wet pulverization method in which magnetite powder is pulverized with a ball mill in water or an organic solvent.

When using the wet grinding method, if an organic solvent such as hexane is used in addition to 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 magnetophyte.

Ferromagnetic oxides such as cobalt ferrite, composite ferrite of these and zinc, and barium ferrite, and fine particles of metals such as iron and cobalt 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 surfactant of the present invention is preferably one selected from alkyl polyphenyl ethers, dialkyl polyphenyl ethers, and alkyl naphthalenes that has a high affinity with the dispersion medium of the present invention.

Therefore, the surfactant of the present invention is a surfactant having a polar group (for example, a sulfonic group, -8O3H) at one end of a compound consisting of an aliphatic hydrocarbon and an aromatic hydrocarbon, and includes petroleum sulfonic acid or a salt thereof, or a synthetic sulfonic acid or a salt thereof.

In particular, when using either petroleum sulfonic acid or synthetic sulfonic acid alone, synthetic sulfonic acid, which has a narrower molecular weight distribution and a smaller number of components than petroleum sulfonic acid, is suitable. However, polar groups are not limited to the above-mentioned sulfone groups, but also include hydroxyl groups and carboxyl groups.

It may be an amino group, a phosphoric acid ester group, etc., and at least one type of acid or base having any of these or a salt thereof can be used.

Furthermore, the surfactant of the present invention is an acid or base having one or more of the above-mentioned polar groups at one end of an aliphatic hydrocarbon polymer having one or more unsaturated bonds; It is also possible to use at least one type of compound having one or more acid anhydrides at one end of an aliphatic hydrocarbon polymer having one or more unsaturated bonds, such as polybutene succinic acid, polybutene succinic acid, Acid anhydride, polybutenesulfonic acid, or ethylene and α-
Examples include cooligomer carboxylic acids with olefins.

The method for producing a magnetic fluid composition of the present invention includes adding the surfactant and a low boiling point solvent to the ferromagnetic fine particles, thereby making the ferromagnetic fine particles whose surfaces are coated with the surfactant have a A step of obtaining an intermediate medium dispersed in a boiling point organic solvent, and after separating fine particles with poor dispersibility in the intermediate medium, adding at least one of alkylnaphthalenes or alkyl polyphenyl ethers to the intermediate medium to form a mixture. and heating the mixture to evaporate the low-boiling organic solvent.

However, in the above manufacturing method, after separating the fine particles with poor dispersibility in the intermediate medium, the intermediate medium is first heated to evaporate and remove the low boiling point organic solvent, and the remaining ferromagnetic fine particles are removed. A magnetic fluid composition may be obtained by adding at least one of alkylnaphthalenes or alkyl polyphenyl ethers as a dispersion medium.

Examples of this invention are listed below.

[Example 1] First, ferrous sulfate and ferric sulfate were each added at 0°3 m
6N Na 0Ha to an aqueous solution IIl containing 0 l each
q was added until the pH reached 11 or higher, and then the solution was diluted with 60
A slurry liquid of magnetite colloid was obtained by aging at ℃ for 30 minutes. Then, the electrolyte in this slurry is removed by washing with water at room temperature. The above is a process for producing magnetite colloid by a wet method.

3N H was added to the magnetite colloid liquid thus obtained.
After adjusting the pH to 3 by adding CII aq, 30% sodium petroleum sulfonate was added as a surfactant.
The surfactant was adsorbed onto the surface of the magnetite particles by adding g and stirring at 60°C for 30 minutes. After that, by standing still, the magnetite particles in the liquid will aggregate and precipitate, and the supernatant liquid will be discarded. Add more water, stir, let stand, and discard the supernatant. This water washing was repeated several times to remove the electrolyte in the aqueous solution, followed by filtration, dehydration, and drying to obtain powdery magnetite fine particles whose surfaces were covered with a surfactant.

Next, by adding hexane as a low boiling point solvent to this magnetite powder and thoroughly shaking it, an intermediate medium in which magnetite particles were dispersed in hexane was obtained. This intermediate medium is centrifuged for 30 minutes under a centrifugal force of 8000 G to sediment and remove relatively large particles with poor dispersibility among the magnetite dispersed particles. Next, the supernatant liquid in which the magnetite fine particles that remained without sedimentation were dispersed was transferred to a rotary evaporator and kept at 90°C to evaporate and remove the low boiling point solvent component, that is, hexane, to obtain lipophilic magnetite fine particles. Ta.

5 g of these magnetite fine particles are collected and redispersed in hexane, and then 4 g of hexadecyl diphenyl ether serving as a carrier is added and mixed. This mixed solution is transferred to a rotary evaporator and maintained at 90°C to evaporate and remove the low boiling point solvent component, ie, hexane. the result,
Magnephyte is dispersed throughout the carrier. This was further centrifuged and processed under a centrifugal force of 8000G for 30 minutes.

This operation removed the undispersed solids, and the colloidal solution above was an extremely stable magnetic fluid.

[Example 2] Magnetite colloid was produced by a wet method in the same manner as in Example 1 above.

After adjusting the pH to 3 by adding 3N HClaq to the magnetite colloid solution, sodium polybutenesulfonate (manufactured by Teikoku Kako Co., Ltd., PO
The surfactant was adsorbed onto the surface of the magnetite particles by adding 40g of 3U) and stirring at 60''C for 30 minutes.Then, by standing still, the magnetite particles in the liquid aggregated and precipitated. , discard the supernatant liquid.

Add more water, stir, let stand, and discard the supernatant. This water washing was repeated several times to remove the electrolyte in the aqueous solution, followed by filtration, dehydration, and drying to obtain powdery magnetite fine particles whose surfaces were covered with a surfactant.

Next, by adding hexane as a low boiling point solvent to this magnetite powder and thoroughly shaking it, an intermediate medium in which magnetite particles were dispersed in hexane was obtained. This intermediate medium is centrifuged for 30 minutes under a centrifugal force of 8000 G to sediment and remove relatively large particles with poor dispersibility among the magnetite dispersed particles. Next, the supernatant liquid in which the magnetite fine particles that remained without sedimentation were dispersed was transferred to a rotary evaporator and kept at 90°C to evaporate and remove the low boiling point solvent component, that is, hexane, to obtain lipophilic magnetite fine particles. Ta.

5 g of these magnetite fine particles are collected and redispersed in hexane, and then 4 g of eicosylnaphthalene as a carrier is added thereto and mixed. This mixed solution is transferred to a rotary evaporator and maintained at 90°C to evaporate and remove the low boiling point solvent component, ie, hexane. As a result, the magnetite is dispersed throughout the carrier. This was further centrifuged and processed under a centrifugal force of 8000G for 30 minutes. This operation removed the undispersed solids, and the colloidal solution above was an extremely stable magnetic fluid.

[Example 3] Magnetite adsorbed with sodium polybutenesulfonate as a surfactant was prepared in exactly the same manner as in Example 2, except that the eicosylnaphthalene used as a carrier in Example 2 was changed to hexadecyl diphenyl ether. A magnetic fluid was prepared by dispersing ferromagnetic particles in hexadecyl diphenyl ether. What was obtained was an extremely stable magnetic fluid.

[Example 4] In the same manner as in Example 1, magnetite colloid was produced by a wet method.

After adding 3N HClaq to the magnetite colloid solution and adjusting its pH to 5, polybutenesuccinic acid (manufactured by Esso: P, B, S, A) 3 was added as a surfactant.
The surfactant was adsorbed onto the surface of the magnetite particles by converting 0g into a sodium salt in advance, adding the resulting aqueous solution, and stirring at 60°C for 30 minutes. After that, by standing still, the magnetite particles in the liquid will aggregate and precipitate, and the supernatant liquid will be discarded. Add more water, stir, let stand, and discard the supernatant.

This water washing was repeated several times to remove the electrolyte in the aqueous solution, followed by filtration, dehydration, and drying to obtain powdery magnetite fine particles whose surfaces were covered with a surfactant.

Next, by adding hexane as a low boiling point solvent to this magnetite powder and thoroughly shaking it, an intermediate medium in which magnetite particles were dispersed in hexane was obtained. This intermediate medium is centrifuged for 30 minutes under a centrifugal force of 8000 G to sediment and remove relatively large particles with poor dispersibility among the magnetite dispersed particles. Next, the supernatant liquid in which the magnetite fine particles that remained without sedimentation were dispersed was transferred to a rotary evaporator, and the low boiling point solvent component, that is, hexane, was evaporated and removed at 90"C to obtain lipophilic magnetite fine particles. Ta.

5 g of these Magnetite 11 particles are collected and redispersed in hexane, and then 4 g of hexadecyl diphenyl ether serving as a carrier is added and mixed. This mixed solution is transferred to a rotary evaporator and kept at 90° C. to evaporate and remove the low boiling point solvent component, ie, hexane. As a result, the magnetite is dispersed throughout the carrier. This was further centrifuged and processed under a centrifugal force of 8000G for 30 minutes.

This operation removed the undispersed solids, and the colloidal solution above was an extremely stable magnetic fluid.

[Example 5] In the same manner as in Example 1, magnetite colloid was produced by a wet method.

3N HCltaq was added to the magnetite colloid solution to adjust its pH to 3, and then 30 g of synthetic sodium sulfonate was added thereto as a surfactant.

The following treatment was carried out in exactly the same manner as in Example 4 above to produce a magnetic fluid in which fine magnetite ferromagnetic particles adsorbing synthetic sodium sulfonate as a surfactant were dispersed in hexadecyl diphenyl ether. What was obtained was an extremely stable magnetic fluid.

The upper colloidal solution was an extremely stable magnetic fluid.

[Example 6] Magnetite adsorbed with synthetic sodium sulfonate as a surfactant was prepared in exactly the same manner as in Example 5, except that hexadecyl diphenyl ether used as a carrier in Example 5 above was changed to eicosylnaphthalene. A magnetic fluid was prepared by dispersing ferromagnetic particles in hexadecyl diphenyl ether. What was obtained was an extremely stable magnetic fluid.

[Example 7] In the same manner as in Example 1, magnetite colloid was produced by a wet method.

Take 5 g of magnetite powder obtained by dehydrating and drying this, add hexane, a low boiling point solvent, and 2.5 g of a surfactant consisting of cooligomer carboxylic acid of ethylene and α-olefin, and use a ball mill for 2 hours. Grind and mix.

Next, this solution was centrifuged at aoooorpm for 1
After treatment for a period of time, the supernatant was removed and 3 g of eicosylnaphthalene as a carrier was added. This was collected in a rotary evaporator and kept at 90°C to remove hexane by evaporation, and then further processed in a centrifugal separator at 8000 rpm for 1 hour. The supernatant liquid was an extremely stable magnetic fluid in which fine magnetite ferromagnetic particles adsorbing the surfactant ethylene, α-olefin, and cooligomeric carboxylic acid were dispersed in eicosylnaphthalene.

In addition, according to each of the above embodiments, ferromagnetic fine particles are once dispersed in a low boiling point solvent to serve as an intermediate medium, and this is centrifuged to remove fine particles with poor dispersibility in advance.

After that, the low boiling point solvent was removed by heating, so
A stable magnetic fluid with low vapor pressure is obtained with high concentration and efficiency.

[Example 8] Table 1 shows the results of comparing the performance of the magnetic fluid obtained by the present invention and the magnetic fluid obtained by the prior art (using polyalphaolefin as a carrier).

As the magnetic fluid obtained in this invention, the magnetic fluid manufactured in Example 5 was used. That is, it is a magnetic fluid in which fine magnetite ferromagnetic particles adsorbing synthetic sodium sulfonate, which is a surfactant, are dispersed in hexadecyl diphenyl ether.

Table 1 (Note): Values after placing 5 cc in a petri dish with a diameter of 5 cm and leaving it in a vacuum device for one day and night.

[Effects of the Invention] According to the present invention, ferromagnetic fine particles are dispersed in a dispersion medium made of at least one of alkyl polyphenyl ethers or alkyl naphthalenes via a surfactant, so that the ferromagnetic particles have a low viscosity. Moreover, it is possible to provide a magnetic fluid composition that has extremely low volatility and hygroscopicity, and high thermal stability, and is optimal as a vacuum sealing agent.

Claims (5)

[Claims] (1) In a magnetic fluid composition in which ferromagnetic fine particles adsorbed with a surfactant are dispersed in a dispersion medium consisting of an organic solution, the dispersion medium is an alkyl having a vapor pressure of 1×10^-^7 Torr or less. A magnetic fluid composition comprising at least one of naphthalenes and alkyl polyphenyl ethers. (2) A surfactant has one or more of a sulfone group, a phosphate ester group, a hydroxyl group, a carboxyl group, or an amino group at one end of a compound consisting of an aliphatic hydrocarbon and an aromatic hydrocarbon. The magnetic fluid composition according to claim 1, which is at least one of an acid or a base or a salt thereof. (3) The surfactant is a polymer of aliphatic hydrocarbons having one or more unsaturated bonds, which has a carboxyl group, a sulfone group, a sulfate ester group, a hydroxyl group, a phosphate ester group, or an amino group at one end. 2. The magnetic fluid composition according to claim 1, wherein the magnetic fluid composition is at least one of an acid or base, or a salt thereof, or a compound having one or more acid anhydrides at one end of the polymer. (4) Adding a surfactant and a low-boiling organic solvent to the ferromagnetic fine particles to obtain an intermediate medium in which the ferromagnetic fine particles whose surfaces are coated with the surfactant are dispersed in the low-boiling organic solvent; , after separating fine particles with poor dispersibility in the intermediate medium, adding at least one of alkylnaphthalenes or alkyl polyphenyl ethers to the intermediate medium to form a mixture; and heating the mixture to form a mixture. evaporating an organic solvent. (5) Adding a surfactant and a low boiling point organic solvent to the ferromagnetic fine particles to obtain an intermediate medium in which the ferromagnetic fine particles whose surfaces are coated with the surfactant are dispersed in the low boiling point organic solvent; , after separating fine particles with poor dispersibility in the intermediate medium, heating the intermediate medium to evaporate the low-boiling point organic solvent; and adding at least one of the above.