JPH0654733B2 - Magnetic fluid manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnetic fluid.

Prior art and its problems As a magnetic fluid, fine particles of an oxide magnetic material (magnetite, Fe ₃ O ₄ ) have already been treated with a surface active agent and dispersed in a colloidal form in oils, water, etc. Things are known and are actually put to practical use in various fields.

However, with magnesium and the like, only saturation magnetizations of 200 to 300 G, and at most 550 to 600 G, have been obtained as magnetic fluids, and therefore when used in practice, small saturation magnetization is a major drawback.

Therefore, development of a magnetic fluid having a large saturation magnetization is desired.

There are two methods for increasing the saturation magnetization: increasing the saturation magnetization of the dispersed fine particles themselves or increasing the content of the fine particles in the medium.

Increasing the concentration of the latter fine particles has a problem in that the magnetic fluid becomes a paste, and therefore, when magnetite is used, it is impossible to obtain more than 600G.

The former magnetic fluid using fine particles having high saturation magnetization is disclosed in US Pat. Nos. 3,228,81 and 3,228,822.
Some are listed in the issue. That is, cobalt carbonyl Co ₂ (Co) ₈ or iron carbonyl Fe (CO) ₅ is thermally decomposed in a polymer such as acrylonitride styrene,
This is a method of dispersing in a hydrocarbon medium.

However, this method uses fine particles with high saturation magnetization, so it is expected to have higher saturation magnetization than magnetite magnetic fluid, but if the concentration of metal fine particles is increased, it becomes paste-like and the concentration cannot be increased. , 300-400
Only G is obtained, and it has no significance compared to magnetite magnetic fluid.

In addition to this, by applying the method of electroless plating, Fe, N
A method of obtaining ferromagnetic fine particles such as i and Co and dispersing them in a suitable medium, exploding Co, Fe and the like in an inert gas to obtain fine particles of these metals, which are placed in a suitable medium. Although dispersion methods and the like have been carried out, neither of the methods has yielded the expected magnetic fluid with high saturation magnetization.

II. Object of the invention The object of the present invention is to obtain a method for producing a magnetic fluid having a significantly higher saturation magnetization than the conventional magnetic fluid.

Such an object is achieved by the present invention described below.

That is, the present invention provides a cobalt carbonyl compound and the above-described interface when a magnetic fluid containing metal fine particles of cobalt, one or more surfactants of fatty acid ester of polyglycerin or sorbitan, and a hydrocarbon-based medium is obtained. A method for producing a magnetic fluid, which comprises heating a solution containing an activator and the hydrocarbon medium.

III Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

In the magnetic fluid using the cobalt metal fine particles of the present invention,
First, since it is indispensable to disperse the ferromagnetic fine particles in the liquid, it is necessary to make the particle size to overcome its magnetic cohesive force.

In the present invention, the cobalt metal fine particles have a particle size of 70 to 120Å
Use the one.

On the other hand, in order to prevent aggregation due to van der Waals' attractive force, oxide magnetic particles are chemically coated with a polar molecule surfactant to prevent aggregation due to repulsion between the particles.

However, no coating agent of this kind has been found in the case of metallic magnetic fluid.

In the present invention, the metal fine particles are stably dispersed in the hydrocarbon medium by using a fatty acid ester-based nonionic surfactant.

That is, the surfactant used is composed of one or more fatty acid esters of polyglycerin or sorbitan.

The fatty acid ester of polyglycerin is represented by the following formula [I].

In the above formula [I], R is a saturated or unsaturated fatty acid-based acyl group or hydrogen. Further, n is a positive integer. In addition, when R is an acyl group, a plurality of R may be different in some cases, but they are usually the same.

In the fatty acid ester of polyglycerin, the degree of polymerization of polyglycerin is 2 to 10, that is, n = 0 to 8, and more preferably n = 4 to 8.

Further, these are preferably partial esters of fatty acids. In this case, the esterification rate is about 25 to 85%.

The fatty acid ester of sorbitan may be a mono-, sesqui (mixture of mono and di) or diester of a fatty acid such as 1,5-sorbitan or 1,4-sorbitan.

However, among these, mono- or sesquiesters of fatty acids of 1,5-sorbitan or 1,4-sorbitan represented by the following formulas [II] and [III] are preferable.

In the above formula [II] or [III], R is a saturated or unsaturated fatty acid-based acyl group.

These fatty acid esters have 10 to 18 carbon atoms,
Particularly preferred are 18 fatty acids, that is, esters of stearic acid, isostearic acid or oleic acid.

Commercially available esters may be used as the above ester.

In order to obtain a high saturation magnetization, it is necessary to make the metal fine particles have a high concentration, but on the other hand, when the high concentration is used, the magnetic fluid is likely to be pasted. In the present invention, this is effectively prevented by using the above-mentioned surfactant.

Specific examples of the surfactant used below will be given.

1) Polyglycerin fatty acid ester I) Decaglyceryl pentaoleate II) Decaglyceryl pentastearate III) Decaglyceryl pentaisostearate IV) Decaglyceryl heptasterearate V) Decaglyceryl heptaisostearate VI) Decaglyceryl heptaolate VII) Decaglyceryl decaisostearate VIII) Decaglyceryl decastearate IX) Decaglyceryl decaurate X) Diglyceryl monooleate XI) Diglyceryl dioleate XII) Tetraglyceryl tristearate XIII) Tetraglyceryl tetrastearate XIV) Tetraglyceryl penta Olate XV) Hexaglyceryl tristearate XVI) Hexaglyceryl pentastearate XVII) Hexaglyceryl pentastearate 2) Sorbitan unsaturated fatty acid ester I ) 1,5-sorbitan monooleate II) 1,4-sorbitan monooleate III) 1,4-sorbitan monostearate IV) 1,4-sorbitan monoisostearate V) 1,4-sorbitan sesquioleate VI) 1 , 4-Sorbitan sesquiisostearate In this case, two or more kinds of these surfactants may be used.

These surfactants to be added are 2 to the metal fine particles.
It is about 5 to 60% by weight.

If it is less than 25% by weight, it is not effective, and if it exceeds 60% by weight, agglomeration and sedimentation of metal fine particles occur in the cooling step after the reaction.

The hydrocarbon used as the medium preferably has 7 to 22 carbon atoms, and paraffin or olefins such as kerosene, aromatics such as toluene and xylene can be used, and particularly for saturated fatty acid ester. Xylene and kerosene are preferable, and for unsaturated fatty acid ester, kerosene is preferable.

The hydrocarbon medium is 50 to 25 with respect to the metal fine particles.
Contains 0% by weight.

To produce such a magnetic fluid, metal carbonyl may be added to a hydrocarbon medium in which a surfactant is dissolved, and the mixed solution may be heated to thermally decompose the metal carbonyl.

Co ₂ (CO) ₈ may be used as the metal carbonyl.

The thermal decomposition temperature is 120 to 180 ° C, and the thermal decomposition time is 2
Approximately 4 hours. The temperature and time may be appropriately changed depending on the concentration of cobalt and the solvent used.

Although the magnetic fluid of the present invention can be obtained by such thermal decomposition, cold resistance and the like can be improved by adding a compatible low-boiling point solvent such as hexane to the obtained magnetic fluid.

Such a magnetic fluid needs to be stored in a predetermined container. Then, it is preferable to replace the inside of the container with an inert gas such as argon or nitrogen.

IV Specific Actions and Effects of the Invention The magnetic fluid obtained by the present invention is C having high saturation magnetization.
o Since the metal fine particles are dispersed in the hydrocarbon-based medium by using the metal fine particles and the nonionic surfactant consisting of one or more kinds of fatty acid ester of polyglycerin or sorbitan, the dispersibility is excellent. It has a much higher saturation magnetization than the magnetic fluid of.

Further, by changing the concentration of the metal fine particles, it is possible to obtain a magnetic fluid having a desired saturation magnetization.

Further, the linearity between the concentration of the metal fine particles and the saturation magnetization is also good over a considerable concentration range of the metal fine particles.

Such an effect can be achieved only by the combination of the fine metal particles, the surfactant and the hydrocarbon medium in the present invention.

V Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown to explain the present invention in more detail.

<Example 1> 12 g of decaglyceryl heptaolate was added to kerosene medium 30.
The solution dissolved in g was placed in a three-necked flask equipped with a condenser, a thermometer, and a stirrer. To this, 120 g of octacarbonyldicobalt Co ₂ (CO) ₈ was added.

This mixed solution was gradually heated with a mantle heater while stirring, and cobalt carbonyl was thermally decomposed while refluxing. At this time, C formed by disassembling from the upper part of the cooler
O is generated.

This generation of CO is caused by a PdCl ₂ solution (acetone: water =
1: 1) to confirm. That is, the orange PdCl ₂ solution turns black by the introduction of CO.

After the generation of CO was completed, stirring was continued for about 30 minutes and then cooled. This produced a black solution.

This black solution was centrifuged at 6000 rpm for 1 hour. However, at this time, there was almost no separation / sedimentation.

By changing the amount of the kerosene medium, it is possible to change the concentration of the magnetic fluid. The relationship between the specific gravity of the obtained solution and the saturation magnetization is shown in Table 1 and FIG. 1 (here, the specific gravity was used as a parameter instead of the concentration).

From these results, it is understood that according to the present invention, extremely high saturation magnetization can be obtained.

According to the Japan Electronic Industry Development Association “Research Report on New Electronic Materials X Magnetic Material Research Report 1”, pages 90 to 94, the polymer coating of the above-mentioned US Pat. No. 322882 only gives about 300 to 400 G. It is said that it cannot be done. Therefore, even in comparison with this, it is clear that the present invention can give higher saturation magnetization.

Further, as is apparent from FIG. 1, the one of the present invention is
The linearity between the saturation magnetization and the specific gravity is also good, which is extremely useful in practice.

Example 2 Instead of decaglyceryl heptaolate in Example 1, 1,
5-Sorbitan monooleate was used. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The relationship between the specific gravity and the saturation magnetization of the obtained solution is shown in Table 2 and FIG.

From these results, the effect of the present invention is clear. Also,
As shown in FIG. 2, the present invention has good linearity between saturation magnetization and specific gravity.

<Example 3> In Example 1, toluene was used instead of the kerosene medium.

However, Co ₂ (CO) ₈ was 30 g, decaglyceryl heptaolate was 30 g, and toluene was 20 g. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation sedimentation.

The specific gravity of the solution was 1.1589, and the saturation magnetization was 490G.

<Example 4> In Example 3, xylene was used instead of the toluene medium. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation sedimentation.

The specific gravity of the solution was 1.3250, and the saturation magnetization was 880G.

<Example 5> In Example 1, decaglyceryl decaolate was used instead of decaglyceryl heptaolate. However, Co
₂ (CO) ₈ was 30 g, decaglyceryl dekarate was 3 g, and kerosene was 20 g. The obtained black solution was centrifuged at 6000 rpm for 1 hour.
Almost no separation and settling occurred.

The specific gravity of the solution was 1.234, and the saturation magnetization was 720G.

Example 6 Instead of decaglyceryl dekarate in Example 5, 1,
4-Sorbitan monooleate was used. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.2003, and the saturation magnetization was 615G.

<Example 7> In Example 5, two kinds of surfactants, decaglyceryl heptaolate and decaglyceryl dekaolate, were used instead of decaglyceryl dekaolate. The obtained black solution was centrifuged at 6000 rpm for 1 hour.
Almost no separation and settling occurred.

The specific gravity of the solution was 1.1854, and the saturation magnetization was 620G.

<Example 8> In Example 4, hexaglyceryl tristearate was used as a surfactant instead of decaglyceryl heptaolate. The black solution obtained was centrifuged at 6000 rpm for 1
Centrifugation was carried out for an hour, but there was almost no separation sedimentation.

The specific gravity of the solution was 1.2009, and the saturation magnetization was 620G.

<Example 9> In Example 8, tetraglyceryl tristearate was used as a surfactant instead of hexaglyceryl tristearate. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.2911, and the saturation magnetization was 688G.

<Example 10> Instead of tetraglyceryl tristearate in Example 9, tetraglyceryl pentastearate was used as a surfactant. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.1273, and the saturation magnetization was 620G.

<Example 11> In Example 5, diglyceryl monooleate was used as a surfactant instead of decaglyceryl dekaolate. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.2478, and the saturation magnetization was 789G.

<Example 12> In Example 11, diglyceryl diolate was used as a surfactant instead of diglyceryl monooleate. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.1583, and the saturation magnetization was 1140G.

<Example 13> In place of diglyceryl monooleate in Example 11, decaglyceryl pentaisostearate was used as a surfactant. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The specific gravity of the solution was 1.1639, and the saturation magnetization was 560G.

<Example 14> 1,4 in place of diglyceryl monooleate in Example 11
-Sorbitan monoisostearate was used as a surfactant. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no separation and sedimentation.

The solution had a specific gravity of 1.2876 and a saturation magnetization of 980G.

<Example 15> In place of diglyceryl monooleate in Example 11, 1,
4-sorbitan sesquioleate was used as a surfactant. The black solution obtained was centrifuged at 6000 rpm for 1
Centrifugation was carried out for an hour, but there was almost no separation sedimentation.

The specific gravity of the solution was 1.2248, and the saturation magnetization was 1150G.

<Example 16> Instead of decaglyceryl heptaolate in Example 4,
1,4-sorbitan monostearate was used as the surfactant. The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no sedimentation.

The specific gravity of the solution was 1.2000, and the saturation magnetization was 757G.

<Example 17> In Example 5, decaglyceryl isostearate was used as a surfactant instead of decaglyceryl dekarate.
The obtained black solution was centrifuged at 6000 rpm for 1 hour, but there was almost no sedimentation.

The specific gravity of the solution was 1.0773, and the saturation magnetization was 870G.

From the above results, the effect of the present invention is clear. That is, it was possible to obtain a stable magnetic fluid having a saturation magnetization of 1000 G or more and a maximum of about 2200 G and having a high saturation magnetization, which has been eagerly developed. In addition, since the concentration of the metal fine particles and the saturation magnetization have a proportional relationship over a considerable concentration range of the metal fine particles, by appropriately changing the concentration of the metal fine particles, a magnetic fluid having a saturation magnetization according to the needs at that time is created. It became possible to do it.

[Brief description of drawings]

1 and 2 show the specific gravity and saturation magnetization of cobalt magnetic fluid when kerosene was used as the hydrocarbon medium and decaglyceryl heptaolate and 1,5-sorbitan monooleate were used as the surfactants, respectively. (4πMs
Is a graph showing the relationship with / G).

Claims (11)

[Claims] 1. A cobalt carbonyl compound and the above-mentioned interface for obtaining a magnetic fluid containing fine metal particles of cobalt, one or more surfactants of fatty acid esters of polyglycerin or sorbitan, and a hydrocarbon-based medium. A method for producing a magnetic fluid, which comprises heating a solution containing an activator and the hydrocarbon medium. 2. The average particle size of the metal fine particles is 70 to 120Å
The method for producing a magnetic fluid according to claim 1, wherein 3. The method for producing a magnetic fluid according to claim 1 or 2, wherein the degree of polymerization of polyglycerin is 2 to 10. 4. The method for producing a magnetic fluid according to claim 1, wherein the fatty acid ester of polyglycerin is a partial ester of fatty acid of polyglycerin. 5. The method for producing a magnetic fluid according to any one of claims 1 to 4, wherein the sorbitan is 1,4-sorbitan or 1,5-sorbitan. 6. The method for producing a magnetic fluid according to claim 1, wherein the sorbitan fatty acid ester is a mono- or sesquiester of sorbitan fatty acid. 7. The method for producing a magnetic fluid according to claim 1, wherein the fatty acid ester is a saturated or unsaturated fatty acid ester having 10 to 18 carbon atoms. 8. The method for producing a magnetic fluid according to claim 7, wherein the fatty acid is stearic acid, isostearic acid or oleic acid. 9. The surface-active agent is contained in an amount of 25 to 25 with respect to the metal fine particles.
The method for producing a magnetic fluid according to any one of claims 1 to 8, which contains 6.0% by weight. 10. The method for producing a magnetic fluid according to any one of claims 1 to 9, wherein the hydrocarbon medium has 7 to 22 carbon atoms. 11. A hydrocarbon-based medium for metal fine particles,
The method for producing a magnetic fluid according to any one of claims 1 to 10, which contains 50 to 250% by weight.