JPH079843B2 - Magnetic fluid composition and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid composition having excellent heat resistance and water resistance and having a low viscosity, which can be suitably used for a shaft seal of a vacuum device, a computer hard disk drive, etc., and a method for producing the same. Is.

[0002]

2. Description of the Related Art As is apparent from the prior art, a magnetic fluid composition is essentially composed of ferromagnetic fine particles, a carrier (dispersion medium), and a dispersant, and the magnetic particle adsorbs (bonds) the dispersant. By doing so, the magnetic particles are uniformly dispersed in the carrier.

By the way, when such a magnetic fluid is subjected to high temperature and high humidity conditions, the dispersant is desorbed from the magnetic particles, and further, water molecules that have penetrated into the carrier are adsorbed on the surface of the magnetic particles and dispersed. The dispersant is irreversibly desorbed from the magnetic particles by replacing the dispersant with the agent. When such a state occurs, the cohesion of the magnetic particles progresses, the magnetic fluid gels, and the initial properties such as an increase in viscosity are lost. In particular, this is a serious problem in the magnetic fluid for sealing, which requires low torque characteristics.

Therefore, conventionally, there are conventional examples in which various improvements have been made to the magnetic fluid in order to improve the heat resistance and water resistance of the magnetic fluid. As such a conventional example, there is a magnetic fluid composition using polybutene succinic acid as a dispersant (US Pat. No. 370059).

[0005]

However, in this conventional example, since the dispersant used for improving the heat resistance and water resistance of the magnetic fluid composition is an oligomer or polymer having a large molecular weight, the magnetic particles are If the dispersant is used in an amount necessary to disperse the magnetic powder, it is unavoidable that the viscosity of the magnetic fluid becomes high. As a result, it has been unsuitable to use a dispersant, which is an oligomer or a polymer having a large molecular weight, in a magnetic fluid for sealing which requires low torque.

That is, in the conventional magnetic fluid, there has been a problem that the viscosity becomes high when trying to improve the heat resistance and the water resistance, and conversely, the heat resistance and the water resistance are lowered when the viscosity is made low.

Therefore, an object of the present invention is to provide a magnetic fluid composition which is excellent in heat resistance and water resistance and has a low viscosity, and a method for producing the same in order to solve such problems.

[0008]

Means for Solving the Problems The present invention, which can solve the above problems by achieving this object, provides a dispersion medium composed of a low-volatile organic solvent, a lipophilic group and a polar group having an affinity with the organic solvent. Having a low molecular weight dispersant, ferromagnetic fine particles whose surface is coated with the dispersant and dispersed in the organic solvent, and have a lipophilic group and a polar group of a polymer chain, in the dispersion medium. The present invention relates to a ferrofluid composition characterized by consisting essentially of an additive added.

The polymer chain of this additive has 25 to 20 carbon atoms.
It preferably consists of 1500 hydrocarbons. And
As a hydrocarbon chain of such an additive, polyethylene,
Mention may be made of at least one of polypropylene, polybutene, polybutadiene, poly (1-decene), polystyrene and cobolimers with respective monomers.
Furthermore, as a polar group of the additive, a carboxyl group and / or
Alternatively, a sulfone group may be mentioned.

The molecular weight of the additive is 500 to 2000.
It is preferably 0. Further, the content of the additive is 0.
It is preferably 5 to 30% by weight. Then, the present invention also comprises adding a low-boiling point nonpolar organic solvent and a dispersant having a lipophilic group having an affinity for the ferromagnetic fine particles to the ferromagnetic fine particles. A step of binding to the surface and then removing the low boiling point non-polar organic solvent to obtain ferromagnetic fine particles whose surface is coated with the dispersant, and washing the ferromagnetic fine particles with a low boiling point polar organic solvent. And a step of adding a low-volatile organic solvent and an additive having a lipophilic group and a polar group of a polymer chain to the washed ferromagnetic fine particles and mixing them. A method for producing a fluid composition, or for ferromagnetic fine particles,
A low-boiling point non-polar organic solvent and a dispersant having a lipophilic group having an affinity for the low-boiling point organic solvent and coating the surface of the ferromagnetic fine particles, whereby the surface is coated with the dispersant. A step of obtaining an intermediate medium in which fine particles are uniformly dispersed in the low boiling point nonpolar organic solvent; a step of washing the intermediate medium with a low boiling point polar organic solvent; and a dispersion in the intermediate medium before or after the washing. A step of separating the ferromagnetic fine particles having poor properties,
After the separation, a step of adding a low-volatile organic solvent to the intermediate medium to form a mixture, a step of heating the mixture to evaporate and separate the low-boiling organic solvent to obtain a magnetic fluid, and a polymer chain in the magnetic fluid And a step of adding an additive having a lipophilic group and a polar group, the method of producing a magnetic fluid composition.

It is also possible to add the additive in the step of adding the low-volatile organic solvent to form a mixture.

[0012]

As a result of intensive studies by the present inventors, when a surfactant having a lipophilic group and a polar group consisting of a polymer chain is added to a magnetic fluid as an additive to be added to a carrier, not as a dispersant, It was found that it is possible to obtain a magnetic fluid composition that can improve the heat resistance and water resistance of the magnetic fluid composition and can maintain a low viscosity without increasing the viscosity.

In order to prevent the viscosity of the magnetic fluid composition from increasing, a low molecular weight dispersant is used. In such a magnetic fluid composition, the dispersant is magnetic particles in an environment of high temperature and high humidity. To remove from. In this case, the dispersant is adsorbed by the water that has penetrated into the carrier, or the dispersants are adsorbed to each other to form micelles, which makes it difficult for the dispersant to be adsorbed again on the association portion of the ferromagnetic fine particles. When such desorption of the dispersant occurs, aggregation of the magnetic particles occurs as described above.

In such a state, when the additive according to the present invention is added to the magnetic fluid, the additive preferentially adsorbs to the dispersant desorbed portion of the magnetic particles, thereby aggregating the magnetic particles. Prevent. The additive according to the present invention is
Since it has a lipophilic group composed of a polymer chain, it has a relatively low affinity for water, and as a result, it can be preferentially adsorbed to magnetic particles without generating micelles with water.
Therefore, the heat resistance and water resistance of the magnetic fluid are improved.

When a polymeric surfactant is used as a dispersant, its content is usually required to be 30% by weight or more from the viewpoint of ensuring sufficient dispersibility of the magnetic particles. However, if such a high molecular weight dispersant is added, heat resistance and water resistance are improved, but an increase in viscosity cannot be avoided.

However, when a low-molecular-weight surfactant is used as the dispersant and a surfactant having a high molecular lipophilic group is used as the additive as in the present invention, the addition amount can be suppressed to a low level. It will be possible. Therefore, the viscosity of the magnetic fluid can be prevented from increasing and the low viscosity can be maintained.
Moreover, since the additive is preferentially adsorbed to the dispersant desorbed portion of the magnetic fluid as described above by adding such an additive, the dispersant can have a low molecular weight. However, it is possible to prevent the viscosity of the magnetic fluid from increasing.

Further, since the additive itself has a strong hydrophobicity, even if it is added to the carrier, the water absorbency of the carrier itself does not become high. In other words, since the hydrophilicity is low and the micelle forming ability in the carrier is low, it is difficult to take in water even when it is not adsorbed on the ferrofluid fine particles. As a result, also from this point, the water resistance of the magnetic fluid composition is not impaired.

The lipophilic group of the additive according to the present invention comprises a polymer chain, and examples of the polymer chain include aliphatic hydrocarbon series and aromatic hydrocarbon series. Examples of the aliphatic hydrocarbon type include at least one of polyethylene, polypropylene, polybutene, polybutadiene, poly (1-decene), and copolymers (co-oligomers) of respective monomers. Here, polybutene includes polybutene in a narrow sense which is a polymer of a mixture of isobutene (= isobutylene) and normal butene (1-butene, 2-butene), polyisobutene which is a homopolymer of isobutene, and isotactic polymer of butene-1. There is Polybutene 1.

Examples of aromatic hydrocarbons include polystyrene, poly (p-divinylbenzene), and their respective monomers and aliphatic hydrocarbon-based monomers such as ethylene and cobolmers (oligomers).

The number of carbon atoms in the polymer chain of the additive is 25
It is preferably ˜1500. Where the carbon number is 2
When it is less than 5, the hydrophobicity of the additive is not sufficient, so that it cannot be preferentially adsorbed to the dispersant desorbed portion of the magnetic particles, and the heat resistance and water resistance of the composition are not sufficiently improved. On the other hand, when the carbon number exceeds 1500, there is a possibility that the increase in viscosity cannot be avoided even if it is added as an additive. Therefore, it is desirable that the number of carbon atoms in the hydrocarbon chain is 25 to 1500.

The content of the additive is preferably 0.5 to 30% by weight based on the magnetic fluid composition. If it is less than 0.5% by weight, the heat resistance and water resistance of the magnetic fluid composition may not be sufficiently improved. On the other hand, if it exceeds 30% by weight, the viscosity of the magnetic fluid may increase and the low torque property may not be exhibited.

The molecular weight of the additive is 500 to 200.
It is preferably 00. If the molecular weight is less than 500, the heat resistance and water resistance of the magnetic fluid may be deteriorated because the hydrophobicity of the additive is not sufficient. Also, 20000
If it exceeds, the viscosity may increase.

As the hydrophilic group of the additive, conventionally existing cation type such as carboxylate, sulfate ester salt, phosphate salt, sulfonate salt, phosphonate salt, amine salt and the like,
It is possible to widely use anionic polar groups.
A plurality of polar groups may be bonded to the polymer chain.

Preferred specific examples of such additives include polybutene succinate, polyisobutylene succinate, polybutene sulfonate, poly α-olefin sulfonate [RCH═CH (CH ₂ ) _n SO ₃ NaR; C
_n H _{2n + 1} ]. A magnetic fluid composition having a low viscosity (50 to 150 cp, 40 ° C.) can be obtained by using such an additive.

As the low volatility organic solvent (carrier) used as a dispersion medium for the ferromagnetic fine particles of the present invention, a mineral oil having a vapor pressure of 1 × 10 ⁻¹⁰ to 1 × 10 ⁻³ Torr (20 ° C.) is used. Various hydrocarbons such as the above, synthetic oils and ethers or esters, or low volatile organic solvents such as silicone oil are appropriately used depending on the application of the magnetic fluid. For example, for use as a sealing agent for magnetic disks, polyalpha (α) olefin oil, alkylnaphthalene oil, hexadecyl diphenyl ether, a mixture of hexadecyl diphenyl ether and octadecyl diphenyl ether, eicosylnaphthalene, tri-2-
Ethylhexyl trimellitate and the like are preferable.

As the ferrofluid particles of the present invention, a magnetite colloid 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 the wet pulverization method is used, when an organic solvent such as hexane is used as the grinding liquid in addition to water, an amount of the dispersion medium described below which forms a monomolecular layer on the surface of the ferromagnetic powder and its particles. It may be crushed for several hours or more in a ball mill after adding.

It is also possible to use a ferromagnetic oxide such as manganese ferrite, cobalt ferrite other than magnetite, a composite ferrite of these with zinc or nickel, barium ferrite, or a ferromagnetic metal such as iron, cobalt, or a rare earth. .

Further, as the ferromagnetic fine particles, in addition to the one obtained by the wet method or the wet pulverization method, those obtained by the dry method can be used. The content of the ferromagnetic fine particles of the present invention is 1 to 20 in a volume ratio which has been generally used conventionally.
The range of% may be, of course, an extremely high concentration of about 70%, if necessary. That is, according to the present invention, the ferromagnetic fine particle concentration is adjusted to a high concentration of 70% by using an intermediate medium in which ferromagnetic fine particles are dispersed in an organic solvent having a low boiling point as described later. be able to. As a result, a magnetic fluid having an extremely high amount of magnetization can be obtained.

The dispersant for the ferromagnetic fine particles used in the present invention is preferably one having a low molecular weight (550 or less) which has a good affinity with the low-volatile organic solvent serving as the carrier. For example, oleic acid or its salt, petroleum sulfonic acid or its salt, synthetic sulfonic acid or its salt, eicosylnaphthalene sulfonic acid or its salt, polybutene succinic acid or its salt, elaidic acid or its salt, erucic acid or its salt, etc. Such as an anionic surfactant which is a hydrocarbon compound having a polar group such as a carboxyl group, a hydroxyl group and a sulfone group, or a nonionic surfactant such as polyoxyethylene nonylphenyl ether, Is used by appropriately selecting from amphoteric surfactants having a cation portion and an anion portion in the molecular structural formula such as alkyldiaminoethylglycine.

A so-called coupling agent can also be used as the dispersant of the present invention. Examples of this coupling agent include, for example, the general formula YpR _4-n SiX _n (P is an integer of 1 or more, n
Is an integer of 1 to 3) or R _4-n SiX _n (n is an integer of 1 to 3)
There are silane coupling agents that can be represented by: Here, Y in the formula is a vinyl group, an epoxy group, an amino group, a mercapto group and other organic functional groups, and R is a hydrocarbon group such as an alkyl group. X is a hydrolyzable group, such as a methoxy group (CH ₃ O—) or an ethoxy group (C ₂
Is H ₅ O-) alkoxy group such as a (R0-).

The alkosyl group of this silane coupling agent is hydrolyzed by water in the air in the aqueous solution or water adsorbed on the surface of the inorganic substance to give a silanol group (--Si--O).
H) is generated. On the other hand, the ferromagnetic fine particles are
It has an OH group (M-0H), and it is considered that a dehydration condensation reaction occurs between them to chemically bond them by a metasiloxane bond (Si-O-M).

The silane coupling agent represented by the general formula YpR _4-n SiX _n is, for example, vinyltriethoxysilane, and the silane coupling agent represented by the general formula R _4-n SiX _n is, for example, octadecyltrimethoxysilane. .

Examples of the coupling agent other than the silane coupling agent of the previous term include, for example, aluminum-based coupling agents made of acetoalkoxyaluminum diisopropylate, which are particularly suitable for nonaqueous systems, titanate-based coupling agents, and chromium-based coupling agents. A coupling agent or the like can be used. These substances also have in their molecular structure an -OH group-bonding alkoxy group and a moiety having affinity for organic substances (for example, an alkoxyacetoacetate group), and the -of the surface of the ferromagnetic fine particles which is a hydrophilic solid. It has the function of forming a strong lipophilic film by chemically bonding with OH groups.

The optimum amount of the coupling agent added is such that the surface of the ferromagnetic fine particles is completely covered with a monomolecular film.
It is determined in consideration of the specific surface of the ferromagnetic fine particles, the water content, the hydrolyzability of silane, the difference in the film formation state, and the like.

In producing the ferrofluid composition of the present invention, if particles having poor dispersibility in the ferrofluid particles are efficiently removed to obtain a highly stable ferrofluid, or in a carrier. In order to obtain a magnetic fluid having a high magnetizing force by increasing the concentration of ferromagnetic fine particles dispersed in the magnetic fluid, the method for producing the magnetic fluid previously proposed by the present applicant (Japanese Patent Laid-Open No. 174495/1983). According to it is efficient.

That is, the ferromagnetic fine particles and the dispersant are
First, it is added to a low-boiling point nonpolar organic solvent such as hexane, benzene, cyclohexane, carbon tetrachloride, chloroform having a boiling point of 85 ° C or lower. As a result, an intermediate medium is obtained in which the ferromagnetic fine particles whose surface is coated with a dispersant are dispersed in a nonpolar low boiling point organic solvent.

At this time, if the ferromagnetic fine particles obtained by the wet method are used, a required amount of a dispersant is added to a suspension of the ferromagnetic fine particles to form a coating phase, which is once washed and dried. After obtaining the hydrophobic ferromagnetic fine particles, a low boiling point nonpolar organic solvent may be added.

Which process is used depends on the type of product,
It is selected according to the purpose of use, required performance, etc. Next, in order to remove the dispersant other than the dispersant having a single molecule adsorbed on the surface of the ferromagnetic fine particles (dispersant having a two-phase adsorption, dispersant dissolved in a low boiling point nonpolar organic solvent). , Wash the intermediate medium in the first half. When the dispersant is two-phase adsorbed on the ferromagnetic fine particles, the particles become hydrophilic and agglomeration of the particles occurs, the affinity with the moisture that has penetrated into the carrier becomes high, and the dispersant is desorbed from the ferromagnetic fine particles. Etc. In addition, when a dispersant that is not adsorbed on magnetic particles is present in a low boiling point non-polar organic solvent, the dispersant is mixed in the low volatility organic solvent (described later) that should serve as a carrier, and the affinity of the carrier for water is increased. It increases to lower the water resistance of the magnetic fluid composition. Therefore, with the intention of solving these problems, the intermediate medium in the first half is washed.

This cleaning liquid has a low boiling point (boiling point is 85
Polar organic solvents (eg, alcohols (methanol, ethanol, etc.), ketones (acetone,
Ethyl methyl ketone, etc.) can be used. When the intermediate medium is washed with a low-boiling polar organic solvent, the dispersant adsorbed on the magnetic particles in two phases and the dispersant dissolved in the low-boiling polar organic solvent are transferred to the low-boiling polar organic solvent. Can be removed.

In this case, depending on the ratio of the amounts of the low-boiling point nonpolar organic solvent and the low-boiling point polar organic solvent, some may be separated into two phases after mixing and one may be dissolved uniformly. For those which are separated into two phases, the following steps can be carried out by separating and removing the phase containing a large amount of the low boiling point polar organic solvent. On the other hand, if it dissolves uniformly, the washed magnetic fluid microparticles will coagulate and precipitate, so it can be collected by filtration, dried, and redispersed in a low-boiling nonpolar organic solvent before the following steps. it can.

Next, the ferromagnetic fine particles having poor dispersibility in the intermediate medium after washing are removed by centrifugation with a centrifugal force of 5000 to 8000G. Since the intermediate medium composed of a low-boiling point nonpolar organic solvent has an extremely low viscosity, centrifugal separation can be performed efficiently.

It is also possible to carry out this centrifugation before washing the intermediate medium. After that, the low-volatile organic solvent as a carrier is added and mixed, and the mixture is heated in the air or in a reduced pressure to heat the low-boiling organic solvent (the low-boiling nonpolar organic solvent and the low-boiling organic solvent mixed in the washing step). (Boiling point polar organic solvent) is evaporated. It is also possible to heat the intermediate medium once to evaporate the low boiling point organic solvent, then add the low volatility organic solvent to the ferromagnetic fine particles, and further evaporate the low boiling point organic solvent, if necessary. Thus, an extremely stable ferrofluid solution is obtained.

Further, in this case, by adding the above-mentioned intermediate medium to the obtained magnetic fluid and heating it repeatedly, the ferromagnetic fine particles were dispersed in a very high concentration and stably. It is also possible to obtain a magnetic fluid.

The additive in the method for producing the magnetic fluid composition of the present invention may be added anywhere during the step of producing the magnetic fluid and after the step of obtaining the intermediate medium, and the additive is added to the finally obtained magnetic fluid. You may add. Further, the additive may be added directly, or a solution previously dissolved in a solvent may be mixed with the magnetic fluid and then the solvent may be removed by evaporation. As the solvent in this case, for example, the following can be used.

Mineral oil such as kerosene, benzene, toluene,
Xylene, alcohol, cellosolve, ethyl acetate, cellosolve acetate, MEK (methyl ethyl ketone), MIBK (methyl isobutyl ketone), 1,1,
1-trichloroethane, chloroform, carbon tetrachloride, D
MF (dimethylformaldehyde), ethyl acetate, etc.

When the additive is added in the intermediate medium step, it may be added by dissolving it in a solvent for the intermediate medium such as hexane. Alternatively, in addition to the solvent,
Additives mixed with the above-mentioned carrier of the magnetic fluid, that is, various hydrocarbons, synthetic oils and organic solvents such as ethers or esters may be added.

In the method for producing a magnetic fluid composition according to the present invention, it is possible not to use the intermediate medium. In this case, a low-boiling point nonpolar organic solvent and a dispersant having a lipophilic group having an affinity for this are added to the ferromagnetic fine particles to bond the dispersant to the surface of the ferromagnetic fine particles. After that, the low-boiling nonpolar organic solvent is removed to obtain ferromagnetic fine particles whose surface is coated with the dispersant, and the ferromagnetic fine particles are washed with a low-boiling polar organic solvent and dried, The magnetic fluid composition according to the present invention can be manufactured by adding a low volatile organic solvent serving as a carrier and the above additives to the magnetic fluid particles.

[0049]

[Example 1]

Example of manufacture of ferrofluid in which additives are added at the end of the process: First, ferrous sulfate and ferric sulfate are added at 0.3 mo, respectively.
To 1 liter of an aqueous solution containing 1 liter each, 6N NaOHaq is added until the pH becomes 11 or more. Then, mix the mixture with 60
Aging at 30 ° C. for 30 minutes gave an aqueous suspension of magnetite colloid. Then, it is washed with water at room temperature to remove the electrolyte in this slurry. The above is the process of producing magnetite colloid by the wet method.

To the magnetite colloidal solution thus obtained, 3N HClaq was added to adjust its pH to 3, then 40 g of synthetic sodium sulfonate as a surfactant was added thereto, and the mixture was stirred at 60 ° C. for 30 minutes. By doing so, the surfactant was adsorbed on the surface of the magnetite fine particles. After that, the mixture is allowed to stand, the magnetite fine particles in the liquid are aggregated and settled, and the supernatant liquid is discarded. Further, add new water, stir, and leave still, and discard the supernatant. This washing with water is repeated several times to remove the electrolyte in the aqueous solution, and then filtration,
It was dehydrated and dried to obtain powdery magnetite fine particles whose surface was coated with a surfactant.

Next, hexane was added to this magnetite powder as a low-boiling point nonpolar organic solvent and shaken sufficiently to obtain an intermediate medium in which magnetite particles were dispersed in hexane.

Methanol as a low-boiling polar organic compound is added to the obtained colloidal solution to cause particles to once aggregate and precipitate, and the supernatant is discarded. As a result, the extra dispersant other than the dispersant in which the single molecule is adsorbed by the fine particles is removed.

Thereafter, the precipitated fine particles are redispersed in hexane to obtain an intermediate medium. This intermediate medium is centrifuged in a centrifugal separator under a centrifugal force of 8000 G for 30 minutes to remove relatively large particles of magnetite dispersed particles having poor dispersibility by sedimentation. Then, the supernatant liquid in which the magnetite fine particles remaining without settling were dispersed was transferred to a rotary evaporator and kept at 90 ° C. to evaporate and remove the low boiling point organic solvent component, that is, hexane to obtain lipophilic magnetite fine particles.

After collecting 5 g of the magnetite fine particles and redispersing in hexane, 4 g of poly-α-olefin (average degree of polymerization: trimer) as a carrier is added and mixed. Transfer this mixture to a rotary evaporator,
The low boiling point organic solvent component, namely hexane, was removed by evaporation at 90 ° C. As a result, the magnetite fine particles are dispersed in the carrier. This is further centrifuged and 800
It was treated for 30 minutes under 0 G of centrifugal force. By this operation, the non-dispersed solid matter was removed, and an extremely stable magnetic fluid was obtained.

Then, polybutene (narrowly defined) succinic acid (average molecular weight 1100) 0.5 was added to the magnetic fluid as an additive.
g to bring the liquid temperature to 60 ° C. and stir well. Thus, the magnetic fluid composition according to the present invention could be obtained. Measurement of Initial Viscosity Next, the initial viscosity of the magnetic fluid composition thus obtained was measured and found to be 70 cp (40
℃). This viscosity is based on the magnetic fluid composition obtained by using polybutene succinic acid as a dispersant (containing 45% by weight of polybutene succinic acid, the type and content of other ferromagnetic fine particles, and the type of carrier). It is understood that the viscosity is sufficiently low as compared with the viscosity [800 cp (40 ° C.)] of the same). Water resistance test Next, in a 50 ml beaker, 10 ml of the magnetic fluid composition according to this example was placed, and the temperature was 80 ° C. and the relative humidity was 70%.
Left for 100 hours. When the viscosity after standing was measured and the viscosity increase value was determined, it was a very small value of 1.5 cp (40 ° C.). On the other hand, the magnetic fluid composition to which the polybutene succinic acid was not added (all other components and contents were the same) had a viscosity increase value of 25 cp (40 ° C.) under the same conditions. . If the water resistance is poor, the ferromagnetic fine particles agglomerate and gel to increase the viscosity increase value.

The results here show that no agglomeration of magnetite fine particles has occurred in the magnetic fluid composition according to the present invention. Therefore, it can be seen that the obtained magnetic fluid composition has good water resistance. Heat resistance test 0.8 ml each of the obtained magnetic fluid composition was placed in a plurality (10 to 20) petri dishes having an inner diameter of φ20, and 170
It was left in a dry heat oven at ℃. One petri dish was taken out every hour. The petri dish taken out was allowed to stand at room temperature (about 20 ° C.) for a while (about 2 hours), and then tilted to confirm the fluidity of the magnetic fluid composition. The heating time until the fluidity disappeared was set to 170 for the sample magnetic fluid composition.
The solidification time at ° C was used as a scale for heat resistance evaluation. If the magnetic fluid composition has poor heat resistance, the ferromagnetic fine particles agglomerate to cause gelation and shorten the solidification time. For comparison, the same test was performed on the magnetic fluid composition to which the polybutenesuccinic acid was not added (all other components and contents were the same) to determine the solidification time.

As a result of this test, the solidification time of the obtained magnetic fluid composition was 25 hours. On the other hand, the solidification time of the magnetic fluid composition for comparison was 9 hours. As is clear from the comparison of the solidification times of the two, it can be seen that the heat resistance of the magnetic fluid composition according to the present invention is greatly improved. [Example 2] Example in which an additive is added in the middle of the step: Through the same steps as in Example 1, lipophilic magnetite fine particles obtained by removing an excessive activator using a low boiling point polar organic solvent were obtained. . After collecting 5 g of these magnetite fine particles and redispersing them in hexane to make an intermediate medium again, poly-α-olefin (average degree of polymerization: trimer) 4 serving as a carrier
g was added. At the same time, 0.5 g of polybutene (narrowly defined) succinic acid (average molecular weight 1100) is added and mixed. This mixed solution was transferred to a rotary evaporator and kept at 90 ° C. to remove the low boiling point organic solvent, that is, hexane by evaporation. as a result,
The magnetite fine particles are dispersed in the carrier. This was further subjected to a centrifuge and treated under a centrifugal force of 8000 G for 30 minutes. By this treatment, the non-dispersed solid matter is removed, and it is possible to obtain a magnetic fluid composition in which magnetite fine particles are stably dispersed.

Then, the initial viscosity was measured by the same method as in Example 1, and a water resistance test and a heat resistance test were also performed by the same method as in Example 1. As a result, an initial viscosity value of 70 cp (40 ° C.) was obtained, and a viscosity increase value related to the water resistance test was 1.5 cp (40 ° C.).
C.) and a solidification time of 25 hours for the heat resistance test. These values show that a magnetic fluid composition having excellent heat resistance and water resistance and a low viscosity can be obtained by this example as well. It is shown that even if the additive is added during the manufacturing process, the same effect as that at the end of the process can be obtained. Example 3 Relationship between Content of Additive and Initial Viscosity / Water Resistance: Magnetic property obtained by changing only the addition concentration of the additive (polybutene succinic acid) added last in the process of Example 1. The initial viscosity of the fluid composition was measured, and at the same time, the water resistance test was performed, and the relationship between the water resistance and the content of polybutene succinic acid was tested. FIG. 1 shows a characteristic diagram obtained by this test.

In FIG. 1, the rate of viscosity change P _i (%) means P _i = [(P ₁ -P ₀ ) / when initial viscosity = P ₀ and viscosity after water resistance test = P _1. P ₀ × 100].

The lower the initial viscosity, the better the low torque property, and the smaller the rate of change in viscosity, the better the water resistance. As is clear from FIG. 1, the added concentration is 0.5 to 3
At 0% by weight, a magnetic fluid composition having a low initial viscosity and a small viscosity change rate can be obtained. [Example 4] Relationship between content of additive and heat resistance: A composition similar to that of Example 1 was prepared except that the content of polybutene succinic acid was variously changed, and the heat resistance described in Example 1 was prepared. A test was conducted on the relationship between the content of boribten (narrowly defined) succinic acid and the solidification time by the same method as the test. FIG. 2 shows a characteristic diagram obtained by this test.

As is clear from FIG. 2, the solidification time is greatly improved by adding polybutene succinic acid (additive) to the magnetic fluid composition containing no polybutene succinic acid. Example 5 A magnetic fluid composition was prepared in the same manner as in Example 2 except that octadecyl diphenyl ether was used instead of poly-α-olefin as the carrier.

The initial viscosity of this magnetic fluid composition was measured, and the water resistance test and heat resistance test described in Example 1 were performed. As a result, the initial viscosity value was 65 cp (40
C.), 1.0 cp (40.degree. C.) as a viscosity increase value, and 40 hours as a solidification time. It is clarified that all of the magnetic fluid compositions prepared above have good heat resistance and water resistance and low torque. [Example 6] An intermediate medium in which magnetite particles were dispersed in hexane was obtained in the same manner as in Example 1. Next, this intermediate medium is transferred to a rotary evaporator and kept at 90 ° C. to evaporate and remove the low-boiling point nonpolar organic solvent component, that is, hexane, and then methanol is added to the low-boiling point polar organic solvent to wash and remove excess surfactant. did. After that, the washed magnetite fine particles were collected by filtration and dried under reduced pressure at 80 ° C. for 3 hours.

10 g of the magnetite fine particles were sampled,
To this, 5 g of octadecyl diphenyl ether as a carrier and 0.5 g of sodium polybutene (narrowly defined) sulfonate (average molecular weight 500) as an additive were added, followed by pulverization treatment with a ball mill for 3 hours. This was put into a centrifuge and treated under a centrifugal force of 8000 G for 50 minutes. This operation removes the non-dispersed solids,
A very stable ferrofluid containing a polybutene derivative containing O ₃ Na groups was obtained.

With respect to the magnetic fluid composition obtained in this example, the initial viscosity was measured, and the water resistance test and heat resistance test described in Example 1 were performed. As a result, the initial viscosity value was 62 cp (40 ° C.), the viscosity increase value was 3.0 cp (40 ° C.), and the solidification time was 21 hours. These all demonstrate that the magnetic fluid composition prepared has good heat resistance and water resistance, and is excellent in low torque. Example 7 Except that the carrier was poly-α-olefin and the additive was polyisobutylene succinic acid (average molecular weight 2000).
A magnetic fluid composition was prepared in the same manner as in Example 6.

With respect to the magnetic fluid composition obtained in this example, the initial viscosity was measured, and the water resistance test and heat resistance test described in Example 1 were performed. As a result, the initial viscosity value was 100 cp (40 ° C.), the viscosity increase value was 1.0 cp (40 ° C.), and the solidification time was 30 hours. These all demonstrate that the magnetic fluid composition prepared has good heat resistance and water resistance, and is excellent in low torque.

The magnetic fluid composition according to the present invention may appropriately contain various characteristic agents in order to impart desired characteristics such as conductivity.

[0067]

As described above, the magnetic fluid composition according to the present invention has a dispersion medium composed of a low volatility organic solvent and a low molecular weight compound having a lipophilic group and a polar group which are compatible with the organic solvent. A dispersant, ferromagnetic fine particles whose surface is coated with the dispersant and dispersed in the organic solvent, and an additive having a lipophilic group and a polar group of a polymer chain and added to the dispersion medium. , And consists essentially of. Therefore, it is possible to provide a magnetic fluid composition having excellent heat resistance and water resistance and having a low viscosity.

According to the method for producing a magnetic fluid composition according to the present invention, the dispersant other than the dispersant that adsorbs monomolecules is washed away, and the ferromagnetic fine particles whose surface is coated with the dispersant are removed. , Directly or through an intermediate medium in which the ferrofluid fine particles are dispersed in a low boiling point organic solvent, the step of adding the additive is added to the step of mixing the low volatile organic solvent. The additive can be contained as an additive in a carrier instead of as a dispersant, and as a result, a magnetic fluid composition having excellent heat resistance and water resistance and also having a low viscosity requires a special manufacturing facility investment. The effect of being able to manufacture at low cost with existing equipment is achieved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the concentration of polybutene succinic acid (additive) added to a magnetic fluid and the rate of change in viscosity / initial viscosity.

FIG. 2 is a characteristic diagram showing the relationship between the concentration of polybutene succinic acid (additive) added to the magnetic fluid and the solidification time.

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Claims (9)

[Claims] 1. A dispersion medium composed of a low-volatile organic solvent, a low molecular weight dispersant having a lipophilic group and a polar group having an affinity with the organic solvent, and the organic solvent whose surface is coated with the dispersant. A ferrofluid composition characterized by essentially consisting of ferromagnetic fine particles dispersed therein and an additive having a lipophilic group and a polar group of a polymer chain and added to the dispersion medium. . 2. The polymer chain of the additive has 25 carbon atoms.
The ferrofluid composition of claim 1, wherein the ferrofluid composition comprises -1500 hydrocarbons. 3. The hydrocarbon chain of the additive is at least one of polyethylene, polypropylene, polybutene, polybutadiene, poly (1-decene), polystyrene, and a copolymer of each monomer. The magnetic fluid composition described. 4. The magnetic fluid composition according to claim 1, wherein the polar group of the additive is a carboxyl group and / or a sulfone group. 5. The molecular weight of the additive is 500 to 200.
The ferrofluid composition according to any one of claims 1 to 4, wherein the ferrofluid composition is 00. 6. The magnetic fluid composition according to claim 1, wherein the content of the additive is 0.5 to 30% by weight. 7. A non-polar organic solvent having a low boiling point and a dispersant having a lipophilic group having an affinity for the same are added to the ferromagnetic fine particles, and the dispersant is applied to the surface of the ferromagnetic fine particles. Binding, and then removing the low boiling point non-polar organic solvent to obtain ferromagnetic fine particles whose surface is coated with the dispersant,
A step of washing the ferromagnetic fine particles with a low-boiling polar organic solvent, and a low-volatile organic solvent and an additive having a polymer chain lipophilic group and a polar group in the washed ferromagnetic fine particles And a step of mixing, the method for producing a magnetic fluid composition. 8. By adding a low-boiling point nonpolar organic solvent and a dispersant having a lipophilic group having an affinity for the low-boiling point organic solvent to the ferromagnetic fine particles to coat the surface of the ferromagnetic fine particles. A step of obtaining an intermediate medium in which ferromagnetic fine particles whose surface is coated with the dispersant are uniformly dispersed in the low boiling point nonpolar organic solvent; and a step of washing the intermediate medium with the low boiling point polar organic solvent. A step of separating the ferromagnetic fine particles having poor dispersibility in the intermediate medium before or after the washing, a step of adding a low-volatile organic solvent to the intermediate medium after the separation to form a mixture, and the mixture. And a step of heating and evaporating and separating the low boiling point organic solvent to obtain a magnetic fluid, and a step of adding an additive having a lipophilic group and a polar group of a polymer chain to the magnetic fluid. A method for producing a magnetic fluid composition. 9. The method for producing a magnetic fluid composition according to claim 8, wherein the additive is added in the step of adding the low-volatile organic solvent to form a mixture.