JPH01184908A - Manufacture of magnetic fluid of excellent dispersibility - Google Patents

Abstract

PURPOSE:To make it possible to easily form a magnetic fluid having excellent dispersibility without specially adding other substance by a method wherein a poor dispersion magnetic fluid obtained by mixing interfacial activator- attracted ferrite superfine grains with the basic oil, having a specific high boiling point, and a dispersant is heat-treated at a specific temperature. CONSTITUTION:The ferrite superfine grains, on which an interfacial activator is attracted, are mixed with the basic oil, having the high boiling point of about 200 deg.C or above, and a dispersant. As the basic oil having the high boiling point of about 200 deg.C or above, pentaerythritol polyester, phosphate and the like may be used besides high quality alkyl replacement naphthalene and dicarboxylic acid high quality alkylester. When a magnetic fluid is obtained in the state of poor dispersibility, the substance of poor dispersibility is heated up to the temperature of about 170 deg.C or above and lower than the decomposition point or boiling point of high boiling point basic oil or less, the temperature of 170-200 deg.C is used in general, by dipping the above-mentioned material in oil bath for about 1.5-5 hours. Then, high boiling point basic oil and a dispersant are added, a stable suspended substance is obtained by conducting the dispersing treatment such as a supersonic treatment for 0.5-3hours or thereabout.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a magnetic fluid with good dispersibility. More specifically, the present invention relates to a method for producing a magnetic fluid with good dispersibility from a magnetic fluid with poor dispersion.

[Conventional technology]

Ferrites obtained by coprecipitation with strong alkali (magnetite, ferrite, Ni-ferrite, Mn-
Sodium oleate, sodium dioctyl sulfone succinate (trade name: Aero
By adding various surfactants that are water-soluble and have ionic hydrophilic groups, such as sol OT), and heating them at 90°C for 30 minutes, the surfactant is added to the ultrafine ferrite particles. After drying the surfactant-adsorbed ferrite ultrafine particles under reduced pressure, the boiling points of higher alkyl-substituted naphthalenes represented by eicosylnaphthalene, dicarboxylic acid dihigher alkyl esters represented by dioctyl sebacate, dioctyl adipate, etc. Dispersion has conventionally been carried out by applying means such as ultrasonic irradiation in high boiling point base oils of about 200° C. or higher.

This is because the dispersion stability of ultrafine particles deteriorates when the magnetic fluid is concentrated, so a base oil with a low vapor pressure and high boiling point is used.
This is intended to prevent the base oil from condensing due to evaporation.

However, when such a dispersion method is used, these base oils do not penetrate into the aggregated powder (ultrafine aggregated particles), so dispersion is often not performed at all. Therefore, dispersants are sometimes used together with the base oil, but there are problems such as the effective dispersants are limited depending on the type of base oil, or it is impossible to obtain a dispersant that exhibits high dispersibility. do.

[Problem to be solved by the invention]

In order to regenerate a magnetic fluid that has become poorly dispersed and obtain a magnetic fluid with good dispersibility, it is necessary to collect the agglomerated powder and use a base oil-dispersant that is known to form a stable temperature characteristic again. A method of adding and dispersing the powder, a method of adding a new dispersant effective for dispersion to form a stent, and a method of adding a solvent compatible with the base oil to deflocculate the flocculated powder to obtain a sludge. etc. are possible.

However, in any of these methods, the initial base oil-dispersant combination that causes poor dispersion 1 cannot form a stable heating temperature, so it is necessary to add other substances such as a new dispersant or peptizing solvent. In need of.

This means that in order to form stable temperature characteristics, there are limitations to the combination of base oil and dispersant, and it is not possible to select an arbitrary dispersant for the base oil. There is.

In particular, in the case of ferrofluid seals, low vapor pressure, high boiling point base oils, which are considered useful base oils, are effective in combination with it in forming ferrofluids with high dispersity. There is a problem in that the amount of dispersant is very small, and therefore, even if an arbitrary dispersant is added to the high-boiling point base oil and a dispersion treatment is performed, poor dispersion often occurs.

An object of the present invention is to provide a method for regenerating a magnetic fluid with good dispersibility from a magnetic fluid with poor dispersion.

[Means to solve the problem]

In order to achieve the above object, in the method for producing a magnetic fluid with good dispersibility according to the present invention, ultrafine ferrite particles adsorbed with a surfactant are mixed with a high-boiling base oil having a boiling point of about 200°C or higher and a dispersant. After heating the resulting poorly dispersed magnetic fluid to about 170° C. or higher, a high boiling point base oil and a dispersant are added again to perform a dispersion treatment.

As the ultrafine ferrite particles adsorbed with a surfactant, conventionally known particles are used as they are after drying, and mixed with a high-boiling base oil having a boiling point of about 200° C. or higher and a dispersant. As the high-boiling base oil having a boiling point of about 200 DEG C. or higher, in addition to the above-mentioned higher alkyl-substituted naphthalenes and dicarboxylic acid di-higher alkyl esters, pentaerythritol polyesters, phosphoric acid esters, and the like can also be used.

Dispersants used in combination with these high-boiling base oils include Tween 80, Span 80, soybean lecithin, erucate, and various commercially available dispersants that can be used as they are. The selection range is also relatively arbitrary since it is not necessary to form stable heating properties when used in combination with oil.

The magnetic fluid obtained by mixing the above components does not require any further treatment if it forms a stable temperature characteristic at this stage, but if the magnetic fluid is obtained with poor dispersion, In such cases, the poorly dispersed substances may be removed at a temperature of about 170°C or higher and below the decomposition point or boiling point of the high-boiling base oil, generally about 170°C to
It is heated to a temperature of 200° C. for about 0.5 to 1.5 hours by a method such as immersion in an oil bath. If the heating temperature is lower than this, most of the particles will settle and no discoloration will be observed, so that the object of the present invention will not be achieved.

By such heat treatment, the ferrite agglomerated powder, for example, the magnetite agglomerated powder, which had formed one defective dispersion, changes color from reddish brown to black. Then again add the high boiling base oil and dispersant (which may be the same or different from those used to form the poorly dispersed magnetic fluid) in the required amounts;
By applying dispersion treatment such as ultrasonic treatment for about 0.5 to 3 hours, a magnetic fluid with stable temperature characteristics can be obtained.

〔Effect of the invention〕

By heating the poorly dispersed magnetic fluid obtained by mixing surfactant-adsorbed ultrafine ferrite particles with a high-boiling base oil and a dispersant, it can easily be easily dispersed without adding any other substances. The dispersing agent can be selected from a relatively wide range of dispersants in this case.

〔Example〕

Next, the present invention will be explained with reference to examples.

Example I FeCQ2・nH2O20g and FeCQ, ・6
After dissolving 050 g of H, each in 100 mQ of water, they were mixed, and a 5N NaOH aqueous solution was added dropwise thereto with stirring at a dropping rate of LO mΩ/min until the pH reached 11. After completing the dropwise addition, heat under reflux at 100°C for 30 minutes, then cool.
Wash with water. The total volume of the washed aqueous suspension was reduced to 500
After adjusting to n+Q, 6 g of sodium oleate is added thereto, heated at 90° C. for 30 minutes, washed with water, and dried.

To 3 g of the obtained surfactant-adsorbed magnetite ultrafine particles, 5 g of higher alkyl naphthalene as a base oil (Lion Products Diffusion Pump Oil-3) and 2 g of a dispersant (Toho Chemical Products Nonal 206) were added, and the mixture was subjected to ultrasonic waves. Process 3
Although this was carried out for several days, a stable heating temperature was not formed and a reddish-brown poorly dispersed material was obtained.

When this poorly dispersed material is immersed in an oil bath at about 180 to 200° C. for 6° and heat-treated, the reddish-brown color changes to black. Thereafter, 8 g of the same higher alkylnaphthalene and 1 g of a dispersant as above were added to each, followed by ultrasonication for about 2 hours, and the resulting suspension was centrifuged to remove the sediment, and a magnetic fluid with good dispersibility was used. I got it. This magnetic fluid has 12
It showed a saturation magnetization of 0G.

Examples 2-10 In Example 1, the base oil and/or dispersant were changed in various ways. In both cases, stable magnetic fluids were obtained, and their saturation magnetizations were measured.

Table 1 7 Soy lecithin l8CfJ8 Dioctyl sebacate
Pegnor hole-8120G9
Soybean lecithin 160GIO span 80 -130G Note 1) Pentaerythritol polyester: NOF Unistar H-4812R Note 2) Pegnol TL-8
: Toho Chemical Products Comparative Example 1 2 g of surfactant-adsorbed magnetite ultrafine particles of Example 1,
A mixture of 10 g of higher alkylnaphthalene and 3 g of dispersant was subjected to ultrasonic treatment for one week, but a reddish-brown substance with poor dispersion remained. When this was centrifuged, most of the magnetic ultrafine particles precipitated.

Comparative Examples 2 to 5 In Comparative Example 1, various changes were made to the base oil and/or dispersant, but all showed poor dispersion.

Table 2 Eka■ Ordinary m&[-- 2 Higher alkylnaphthalene pegnol TL-83 Tween 80 4 Dioctyl sebacate 〃5
Soybean Lecithin Comparative Examples 6 to 10 In Comparative Example 1, various changes were made to the base oil and/or dispersant, and ultrasonic treatment was combined with a homogenizer to facilitate dispersion. The fine particles settled out.

Table 3 Base oil -
-3H Kuben 1-16 Pentaerythritol Polyester Pegnol TL-87 Soy Lecithin 8 Tween 8
09 Tricresyl phosphate

Claims (1)

[Claims] 1. After heating the poorly dispersed magnetic fluid obtained by mixing ultrafine ferrite particles on which a surfactant has been adsorbed with a high-boiling base oil with a boiling point of about 200°C or higher and a dispersant to a temperature of about 170°C or higher, the high-boiling group is added again. A method for producing a magnetic fluid with good dispersibility, which comprises performing a dispersion treatment by adding oil and a dispersant.