JPH01207131A - Production of magnetic fluid - Google Patents

Abstract

PURPOSE:To efficiently produce a magnetic fluid comprising fine ferrite particles dispersed safely in a base oil of low vapor pressure by adding fine ferrite particles and a dispersant to a base oil having low vapor pressure, and distilling off a hydrocarbon solvent having low boiling points by heating. CONSTITUTION:A stable suspension is prepd. by dispersing fine ferrite particles, to which a surface active agent such as higher fatty acid salt(e.g., sodium oleate, etc.), is adsorbed, are dispersed in a hydrocarbon solvent having low vapor pressure, such as n-hexane, etc. A base oil having low vapor pressure such as a mineral oil having <=0.1mm Hg vapor pressure at 25 deg.C, and a dispersant comprising a nonionic surface active agent such as alkenyl succinimide, phosphoric ester contg. mono- or dioxy alkylene group, or polyether type nonionic surface active agent are added to the suspension. Finally the low boiling hydrocarbon solvent is distilled off by heating at >= about 70 deg.C. Thus, a magnetic fluid contg. fine ferrite particles dispersed easily and stably in a base oil of low vapor pressure is produced efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a magnetic fluid. More specifically, the present invention relates to a method for producing a magnetic fluid in which fine ferrite particles are stably dispersed in a low vapor pressure base oil.

[Prior art] and [Problem to be solved by the invention]
Magnetic fluids are generally made by dispersing fine ferrite particles in base oil using a dispersant such as a higher fatty acid salt or sorbitan ester. However, simply dispersing ferrite fine particles in a low vapor pressure base oil fails to provide high dispersibility, making it extremely impractical.

Even if a fairly good dispersibility is obtained when dispersing in such a low vapor pressure base oil, the low vapor pressure base oil exhibits a kinematic viscosity (at 40°C) below ICr when used in general organic solvents and water. However, since it has a high kinematic viscosity of about 8 to 50 Cst (40° C.), it takes a very long time to form a uniform suspension. Moreover, not all ferrite particles that should be dispersed form a stable suspension.
There is also the problem that a considerable proportion of ferrite fine particles are removed during purification such as centrifugation, resulting in very low efficiency.

An object of the present invention is to efficiently produce a magnetic fluid in which ferrite fine particles are stably dispersed in a low vapor pressure base oil.

[Means to solve the problem]

In order to achieve this object, in the present invention, a magnetic fluid is produced by adding a suspension of surfactant-adsorbed ferrite fine particles to a low-boiling hydrocarbon solvent dispersion at 25°C. A low vapor pressure base oil having a vapor pressure of less than 1 mm Hg and a dispersant which is an alkenyl succinimide, a phosphate ester or polyether type nonionic surfactant having a mono- or di-oxyalkylene substituent are added, This is carried out by heating to a temperature of 70° C. or higher and distilling off the low-boiling hydrocarbon solvent.

In the method of the present invention, first, a surfactant is adsorbed.
Fine ferrite particles with a particle size of about 50 to 300 particles, preferably about 70 to 120 particles, are dispersed in a low-boiling hydrocarbon solvent that disperses them relatively easily, and a stable low-boiling hydrocarbon-based suspension is formed therein. Forming is performed by conventional methods.

Surfactants adsorbed on ferrite particles include:
The following materials that are commonly used when dispersing fine particles in a low-boiling hydrocarbon solvent are used, and higher fatty acid salts or sorbitan esters are preferably used.

higher fatty acid salts oleic acid, such as sodium oleate;
Higher fatty acid aerosols such as stearic acid - dialkyl sulfosuccinates such as 〇T polyoxyethylene alkyl esters alcohol sulfate esters such as dodecyl sulfate esters alkylbenzenesulfonic acids phosphates such as oleyl phosphate polyoxyethylene alkylamine glycerin esters amino alcohols As the ester low-boiling hydrocarbon solvent, an aliphatic, alicyclic or aromatic hydrocarbon solvent having a boiling point of about 60 to 200°C, such as n
At least one of -hexane, n-heptane, n-octane, isooctane, n-decane, cyclohexane, toluene, xylene, mesitylene, ethylbenzene, petroleum ether, petroleum benzine, naphtha, ligroin, etc. is used.

The above surfactant-adsorbed ferrite fine particles are dispersed using these low-boiling hydrocarbon solvents and a homogenizer, and if necessary, centrifuged to remove sediment, resulting in a dispersion concentration of about 0.01 to 30% by weight. , preferably about 0.1-2
A suspension of 0 weight 2 is formed. If the concentration is higher than this, the ferrite particles will gel and will not form a stable suspension.

A low vapor pressure base oil and a second dispersant are then added to this stable low boiling hydrocarbon based suspension and
The low-boiling hydrocarbon solvent is distilled off by heating to a temperature of 0.degree. C. or higher.

As a low vapor pressure base oil, 0.1+u+H at 25℃
Liquids having a vapor pressure of 0.01 mmHg or less, preferably 0.01 mmHg or less, such as natural oils such as mineral oil and spindle oil, or synthetic oils such as higher alkylbenzenes, higher alkylnaphthalenes, and polybutenes (with a molecular weight of 300 to 20
00), dicarboxylic acid diesters (dioctyl azelate, dioctyl adipate, dioctyl sebacate, dibutyl phthalate, dibutyl frate, etc.), polyol polyesters (neopentyl glycol, trimethylolpropane).

Polyesters of polyols such as pentaerythritol and dipentaerythritol and carboxylic acids having 6 to 10 carbon atoms, such as trimethylolpropane tri-n-heptyl ester, pentaerythritol tetra-n-hexyl ester, pentaerythritol tetra-2-ethylhexyl ester, etc.) Phosphate triesters (tributyl phosphate, tri2-ethylhexyl phosphate, tricresyl phosphate, etc.) have a dispersion concentration of ferrite particles in the final magnetic fluid of about 1
It is used in a proportion of 0 to 40% by weight.

The following three types of second dispersants are generally used in a weight ratio of about 0.1 to 1 for these low vapor pressure base oils.

(1) Alkenylsuccinimide (2) Mono- or di-oxyalkylene group-containing phosphoric acid ester or mixture thereof HRO(Co112nO)4+1, -P=0n:
2 or 3 (3) Polyether type nonionic surfactant R-〇-(O
CnlI2r1)4~. 40HR: C, ~C12 alkyl group n: 2 or 3 A low boiling point hydrocarbon-based suspension to which a mixture solution of these low vapor pressure base oils and a second dispersant is added,
It is generally heated to about 70 DEG to 140 DEG C., with stirring, and the low-boiling hydrocarbon solvent is distilled off therefrom, if necessary under reduced pressure. The mixture solution is generally added prior to heating, but may also be added during the distillation and concentration process.
However, it must be added before the concentration progresses too much and agglomerated powder is generated.

If the heating temperature is lower than this, for example at a temperature in a water bath, the generation of agglomerated powder will be noticeable and the desired magnetic fluid will hardly be obtained. There is no problem if the temperature is below the thermal decomposition temperature of the oil, but there is no particular reason why a higher temperature is required in the actual concentration process. In this way, the low boiling hydrocarbon solvent is distilled off, leaving a magnetic fluid therein forming a stable suspension in a low vapor pressure base oil.

〔Effect of the invention〕

By the method of the present invention, a magnetic fluid in which ferrite fine particles are easily and stably dispersed in a low vapor pressure base oil can be efficiently produced.

〔Example〕

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

Example I FeCQ, 20 g of nH2O and FeCQ a
- Dissolve and mix 2050 g of 6H in 100 m Q of water, and then add a 6N NaOH aqueous solution dropwise thereto while stirring at a dropping rate of 10 mL/min until the pH becomes 11. After the dropwise addition is completed, the mixture is heated under reflux at 100° C. for 30 minutes, cooled, and washed with water. The total volume of washed aqueous suspension was
After setting the temperature to 0 mQ, 6 g of sodium oleate was added thereto, heated at 90° C. for 30 minutes, washed with water, and dried.

15 g of the obtained sodium oleate-adsorbed magnetite ultrafine particles and n-octane 2GOn+Q were treated using a homogenizer at a rotation speed of 110,000 rpm for 60 minutes.

It was centrifuged (10,000 rpm, 30 minutes) and the supernatant was collected to obtain a stable suspension with a magnetite dispersion concentration of 3.8% by weight.

This n-octane based suspension 200m Q has alkylnaphthalene (Lion product pump oil-8
) and a commercially available phosphoric acid ester mixture (Toho Kagaku GAFACRE610) as a dispersant.
g was added thereto, and n-octane was distilled off using a rotary evaporator while heating on an oil bath at 70 to 90°C to obtain a magnetic fluid stably dispersed in alkylnaphthalene.

No sediment was observed in the obtained magnetic fluid even after centrifugation, the magnetite dispersion concentration was 24% by weight, and the saturation magnetization was 160G.

Example 2 In Example 1, the same amount of xylene was used instead of n-octane to obtain a stable suspension with a magnetite dispersion concentration of 4.4% by weight.

This xylene based suspension 200 vs Q L
This, alkylnaphthalene (pump oil-8) and polybutenyl succinimide as a dispersant (Toho Chemical Products P
Add 10 g of a 2:1 mixed solution with D-98A) and
The mixture was heated to 90° C. under vacuum for 60 minutes, and then the temperature was increased to 130° C. to distill off the xylene, yielding a magnetic fluid stably dispersed in the alkylnaphthalene.

No sediment was observed in the obtained magnetic fluid even after centrifugation, the magnetite dispersion concentration was 33% by weight, and the saturation magnetization was 230G.

Example 3 To the stable xylene-based suspension 300m Q obtained in Example 2, pentaerythritol polyester (NOF Unistar 14812R) and a commercially available phosphoric acid ester mixture as a dispersant (Toho Kagaku GAFAc RM410) were added. 10g of the mixed solution was added, heated to 100-130°C under vacuum to distill off xylene, and then centrifuged to remove about 0.0% of the sediment.
3 g was removed to obtain a ferrofluid stably dispersed in pentaerythritol polyester.

The obtained magnetic fluid had a magnetite dispersion concentration of 34% by weight and a saturation magnetization of 250G.

Example 4 To 20 g of sodium oleate-adsorbed magnetite ultrafine particles used in Example 1, 3 g of isooctane 200IIQ and dispersant Tween 80 were added, treated with a homogenizer, centrifuged to remove sediment, and the magnetite dispersion concentration was 7. A stable suspension of .6% by weight was obtained.

This isooctane-based suspension 200iIQ was mixed with tricresyl phosphate and a commercially available phosphate ester mixture (R
Add 15 g of a 3:2 mixed solution of E610) and
After heating to 140° C. to remove isooctane, about 0.3 g of sediment was removed by centrifugation to obtain a magnetic fluid stably dispersed in tricresyl phosphate.

The obtained magnetic fluid had a magnetite dispersion concentration of 27% by weight and a saturation magnetization of 170G.

Example 5 To 250 mΩ of the stable n-octane-based suspension obtained in Example 1, 10 g of a 4=1 mixed solution of dioctyl sebacate and a nonionic surfactant (Toho Chemical Products Nonal 210) was added to give a 70-120 mΩ After heating to 0.degree. C. under vacuum to distill off n-octane, about 1.1 g of sediment was removed by centrifugation to obtain a magnetic fluid stably dispersed in dioctyl sebacate.

The obtained magnetic fluid had a magnetite dispersion concentration of 20% by weight and a saturation magnetization of 140G.

Example 6 In Example 1, Tween 80 (sorbitan oleyl ester) adsorbed magnetite ultrafine particles (12 g of Tween 80 was used instead of sodium oleate in Example 1,
A stable n-octane base suspension with a magnetite dispersion concentration of 2.8% by weight was obtained by using 15 g of 15 g of the sample obtained by heating at 90°C for 90 minutes, and the sediment was not collected even after the same treatment and centrifugation. An unrecognizable magnetic fluid (magnetite dispersion concentration 24 weight gourd, saturation magnetization 160G) was obtained.

Comparative Example 1 To 250 m of the stable n-octane-based suspension obtained in Example 1, 7 g of alkylnaphthalene was added.
and 4g of sodium oleate, 70-100
After distilling off n-octane by heating to .degree. C. under vacuum, centrifugation treatment caused separation, and all the ultrafine magnetite particles were precipitated.

Comparative Example 2 To the stable isooctane-based suspension 200+nΩ obtained in Example 4, 15 g of a 3:1 mixed solution of alkylnaphthalene and a commercially available phosphate ester mixture (RE610) was added, and the mixture was heated in a water bath (15 to 25°C) under vacuum. Distilling off the isooctane at the bottom resulted in separation and no ferrofluid was formed.

Comparative Example 3 In the same manner as in Example 1, a stable n-hexane-based suspension (magnetite dispersion concentration 3.5 weight phantom) was formed, and this n-hexane-based suspension 2001IQ was mixed with alkylnaphthalene and polybutenyl succinate. 4:1 mixed solution with acid imide (PD-98A) 10
After adding g and distilling off n-hexane under vacuum in a water bath,
When a fluid with a magnetite dispersion concentration of 3.2% by weight was centrifuged, most of the ultrafine magnetite particles (approximately 6.6 g) sedimented, making it impossible to form a magnetic fluid.

Comparative Examples 4-5 Stable n-octane-based suspension obtained in Example 6 250+a Q with 7 g of alkylnaphthalene
and 4 g of Tween 80 (Comparative Example 4) or sodium oleate (Comparative Example 5) were added and heated to 70-100°C under vacuum to distill off n-octane, followed by centrifugation to cause separation and all The ultrafine magnetite particles have settled.

Claims (1)

[Claims] 1. A 0.1 m
A low vapor pressure base oil having a vapor pressure of less than mHg and a dispersant which is an alkenyl succinimide, a phosphate ester or polyether type nonionic surfactant having a mono- or di-oxyalkylene substituent are added; A method for producing a magnetic fluid in which fine ferrite particles are stably dispersed in a low vapor pressure base oil, which comprises heating to a temperature of 70° C. or higher to distill off a low boiling point hydrocarbon solvent.