JP2000124021A - Magnetic fluid component and formula - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve chemical stability by covering with surface modifying agent a region which is not covered with surface active agent on the surface of a magnetic particle. SOLUTION: A magnetic fluid consists of magnetic particles at 0.1-40 volume percent, surface active agent at 0.1 to about 33 volume percent, an organic carrier medium at 10- about 99 volume percent and surface modifying agent or addition agent at 0.01 to about 25 volume percent. To cover an exposed surface region of the magnetic particle uncovered with surface active agent, surface-modifying agent or addition agent is added at low molecular weight. The addition agent includes acid-based addition agent and amine-based addition agent, and surface active agent includes silane-based surface active agent and titanium-coupling agent. Acetic acid and benzoic acid are used in the acid-based addition, allantoic acid and tripropylamine are used in the amine-based addition agent. After organic carrier medium are molded at high molecular weight, the magnetic particles are scattered when the carrier medium is vaporized at raised temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to chemically stable ferrofluid compositions and methods of making such compositions.

[0002]

2. Description of the Related Art Generally, a magnetic fluid used for technical applications, called "ferrofluid", has a particle size of 30%.
Is a dispersion liquid of magnetic ultrafine particles dispersed in a dispersion medium in a range of 1 to 150 Å.

[0003] Magnetic particles are typically covered with a surfactant or dispersant. Most industrial applications using magnetic fluids have mixed iron oxide as magnetic particles.
For ferrofluid applications, the most suitable iron oxides are ferrites such as magnetite (Fe ₃ O ₄ ) or gamma iron oxide (Fe ₂ O ₃ ). Ferrites and ferric oxide provide many physical and chemical properties to magnetic fluids, the most important of which are saturation magnetization, viscosity, magnetic stability, and chemical stability of the entire system. It is. The amount of magnetic particles in the magnetic fluid composition can be up to 40% by volume.

[0004] Surfactants have two main functions.
The first is to ensure a permanent distance between the magnetic particles in order to overcome the van der Waals force and the attractive force of the magnetic action. The purpose is to provide the surface layer of the covered particles with a chemical composition that is compatible with the chemical. Most of the magnetic fluids used today have one to three surfactants arranged in one, two, or three layers around the magnetic particles. Surfactants for ferrofluids are long chain molecules having a chain length of at least 16 atoms, such as a carbon or carbon-oxygen chain, and a functional group at one end. The functional group is
It can be cationic, anionic or non-ionic.
The functional groups are adsorbed to the surface layer of the oxide (magnetic particles) by chemical bonding, physical force, or a combination of both, and the chains or tails of the surfactant are permanently attached between the particles. And provides compatibility with the optimal distance and the dispersion medium. For all practical purposes, the amount of surfactant in the magnetic fluid can be up to 30% by volume.

[0005] The dispersion medium is generally a polar or non-polar organic molecule, and has a molecular weight of up to 5000 such as hydrocarbon (polyalphaolefin, aromatic chain type molecule), esters (polyolesters), silicone, Or, they are various chemical compositions such as fluorinated molecules and other specially structured molecules.

There are physical and chemical properties of magnetic fluids related to the type of dispersion medium, such as viscosity, evaporation rate, resistance, and compatibility with the surrounding environment.

There are a number of patents relating to the production of magnetic fluids, the most relevant to the present invention are:

US Pat. No. 3,531,413 states that magnetic particles are separated from the initial solvent by first dispersing the magnetic particles in a non-polar solvent and then aggregating the magnetic particles with a polar solvent. And it describes a manufacturing method that is redispersed in a different solvent.

US Pat. No. 3,917,538 describes a process which comprises grinding coarse magnetic particles in an aqueous dispersion medium using a dispersant. The magnetic fluid obtained by the pulverization step and using the water as a dispersion medium is aggregated, and the magnetic particles are separated from the aqueous solution. The particles are then washed and dried and redispersed in an organic dispersion medium using a second surfactant.

[0010] US Patent No. 3,700,595 discloses at least one surfactant which is soluble in oil and insoluble in water.
It describes the use of carboxylic acids having two carbon chains or high molecular weight polyisobutene carboxylic acid surfactants.

US Pat. No. 4,280,918 describes a process for making a magnetic dispersion for use in magnetic coatings. Magnetic particles are a uniform substance,
Preferably, it is covered with colloidal silica. The coating prevents aggregation of the magnetic particles. The pH of the suspension is adjusted to between 3 and 6 with an acid to create a positive electrostatic charge on the surface of the magnetic particles and mix with the colloidal silica having a negative electrostatic charge. The two oppositely charged particles stick together and the silica particles irreversibly bind to the magnetic particles.

US Pat. No. 4,315,827 has one polar functional group that reacts with the surface of magnetic particles and a tail containing a phenyl, benzyl, or phenoxy group that can be dissolved in a dispersion medium. A method for producing a stable magnetic fluid composition by dispersing magnetic particles in polyphenyl ether using a surfactant is described.

US Pat. No. 4,356,098 provides magnetic ultrafine particles in a liquid silicone oil as a dispersion medium, a functional group forming a chemical bond with the surface of the magnetic particles, and a stable magnetic fluid composition. A method for making a stable silicone oil ferrofluid composition comprising the necessary amount of silicone oil surfactant for dispersing, including a tail portion soluble in the dispersing medium silicone oil. The tail part of the surfactant becomes soluble in silicone oil,
It has many atoms of an oxygen chain, or siloxane.

US Pat. No. 4,430,239 discloses a colloid comprising magnetic ultrafine particles in a dispersion medium and a dispersant in an amount required for dispersion comprising a phosphate ester of a long-chain alcohol compatible with a polar dispersion medium. Describes a stable ferrofluid composition comprising a liquid dispersion.

US Pat. No. 4,576,725 describes a method for producing a magnetic fluid by dispersing metal magnetic particles having an average particle size of several hundred angstroms in a dispersion medium. The particles are obtained by condensing metal vapor in a dispersion medium. The metal magnetic particles in the magnetic fluid are rapidly oxidized. The process of oxidation of the metal particles will dramatically change the initial properties of the magnetic fluid.

US Pat. No. 4,599,184 describes an attempt to improve the oxidation and magnetic stability of magnetic metal particles resulting from the condensation of metal vapor by covering the particles with a surfactant. ing. In order to obtain a stable ferrofluid, the particles must be covered with a surfactant, as in the other steps for obtaining a stable ferrofluid.

US Pat. Nos. 4,604,229 and 4,
No. 687,596 describes a method for producing a stable conductive magnetic fluid using a high molecular weight cationic surfactant and a polar dispersion medium.

US Pat. No. 4,608,186 describes a magnetic fluid comprising cobalt metal microparticles and a surfactant selected from the group consisting of polyglycerin fatty acid esters, sorbitan fatty acid esters and mixtures thereof. The dispersion medium is a hydrocarbon. The composition includes tocopherol as an antioxidant additive.

US Pat. No. 4,624,797 is selected from the group consisting of cobalt metal microparticles, an oil-soluble anionic sulfosuccinate and a nonionic polyglycerin fatty acid ester or polyethylene glycol alkyl ether group. A ferrofluid comprising a surfactant and a low volatility solvent is described.

Metal magnetic particles having a particle size of less than 200 angstroms and uniformly covered with a surfactant,
Extremely unstable and oxidizes rapidly. Today, there is no commercial application of such magnetic fluids using magnetic metal particles. The main disadvantage of this process is the oxidation of the magnetic particles.

US Pat. No. 4,938,886 comprises magnetic particles, a dispersant of the formula A—X—B adsorbed on the magnetic particles, and a dispersion medium that is a thermodynamically good solvent for A. A superparamagnetic fluid is described. Where A is O
H-terminated, derived from a nonionic surfactant precursor selected from the group consisting of ethoxylated or propoxylated alcohols and other ethoxylated compounds, B is a dispersant Carboxylic acids adsorbed on the surface of the magnetic particles, and X is a bond between A and B.

US Pat. No. 5,013,471 describes a magnetic fluid in which particles are covered with a silane chloride-based surfactant having a chain of 10 to 25 carbon atoms. A fluorine atom replaces a carbon atom of a hydrocarbon chain of a silane chloride-based surfactant, and a fluorine-based oil is used as a dispersant. No other surfactant was used in this step. According to this reference, silane chloride surfactants are large enough to disperse the particles and must provide sufficient distance between the particles to ensure the colloidal stability of the magnetic fluid.

One of the objects of the present invention is the presence of surfactants which, for example, have 1 to 10 carbon atoms and whose tail covers a free (exposed) surface which is not covered by high molecular weight surfactants Like a tail that can enter between
A very low molecular weight silane-based surface modifier is used. According to the present invention, the silane cannot disperse magnetic particles by itself.

US Pat. No. 5,064,550 describes a superparamagnetic fluid which is a stable colloid of a non-polar hydrocarbon-based dispersion medium, the magnetic particles of which contain at least 19 carbon atoms and which contain at least 19 carbon atoms. An organic acid containing only carbon and hydrogen atoms in the chain to which the group is attached; and
Organic acids and amino acids are coated with at least one acid selected from the group consisting of amino acids acrylated with fatty acids that are branched, unsaturated, or both, increasing the viscosity of the superparamagnetic fluid To do so, an ashless polymer is provided.

US Pat. No. 5,085,789 basically describes a ferrofluid composition comprising ferromagnetic fine particles, an alkyl naphthalene as a dispersion medium, and a surfactant having a hydrophobic group moiety having an alkyl naphthalene structure. ing.

US Pat. No. 5,124,060 basically discloses a magnetic material comprising an organic solvent, ferromagnetic particles covered with a lipophilic group having an affinity for the organic solvent, and a fluorine-based surfactant. It talks about fluids.

US Pat. No. 5,143,637 describes a ferrofluid comprising ferromagnetic particles dispersed in an organic solvent, a low molecular weight dispersant, and an additive having between 25 and 1500 carbon atoms. I have. Low molecular weight dispersants are used to disperse the particles in an organic dispersion medium. As an overview of this reference, there is a discussion about using coupling agents such as silanes as dispersants. However, the coupling agent must have a sufficiently large molecular weight to act as a dispersant. It should be noted that US Patent No. 5,143,637 does not have a specific disclosure claim regarding the use of silanes, even as an additive or even as a dispersant. The thermal stability of the magnetic fluid is increased by adding a polymeric additive such as, for example, a polystyrene, polypropylene, polybutene or polybutadiene polymer having a molecular weight of up to 20,000.

US Pat. No. 5,147,573 discloses a dispersant consisting essentially of superparamagnetic particles, a conductive organometallic compound, a nonionic, anionic or cationic surfactant, and a hydrocarbon organic solvent. A method for producing a colloidal dispersion of conductive magnetic particles comprising

US Pat. No. 4,554,088 uses a silane polymer as a coupling agent. The coupling agent is a special type of surfactant having functional groups at both ends of the long chain molecule. One end of the molecule is adsorbed on the oxide layer on the surface of the magnetic particles, and the other end of the molecule is a drug,
It is bound to a specific compound depending on the intended use, such as an antibody or an enzyme.

US Pat. No. 5,240,628 describes N-
A water-insoluble or almost insoluble organic solvent solution of the polyalkylene polyamine-substituted alkenyl succinimide is added to an aqueous suspension of ferrite fine particles, the resulting mixture is emulsified by stirring, and N-
The polyalkylene polyamine-substituted alkenyl succinimide is adsorbed on the ferrite fine particles, and water and the organic solvent are evaporated. A process for making a magnetic fluid comprising dispersing in a low vapor pressure base oil of 1 mmHg or less is described.

[0031]

Among the patents discussed so far, no attempt has been made to cover the surface of magnetic particles that have not yet been covered by a large surfactant.

To be used in current industrial applications, magnetic fluids must exhibit stability in two areas. First, magnetic particles must be magnetically stable under very high magnetic field gradients because they tend to aggregate under high magnetic field gradients and separate from the remaining colloidal parts. No. Second, it must have chemical stability with respect to the oxidation of the surfactant and the organic oily dispersion medium. All organic oils, sooner or later, will undergo an oxidation process over time,
It increases with temperature and also with the oxygen concentration in the surrounding environment where the oil comes into contact. This oxidation process results in an increase in the viscosity of the oil to the point where the oil gels or solidifies. Also,
There is also a different mechanism whereby molecules break down and evaporate faster from the system. This is the most important condition to ensure a chemically stable colloid exposed to oxygen or high temperatures.

[0033]

SUMMARY OF THE INVENTION The present invention provides a method for measuring a volume of 0.1.
-40 parts of magnetic particles, 0.1 to about 30 parts of at least one surfactant, 10 to about 99 parts of organic dispersion medium, and 0.01 to improve chemical oxidation of their composition.
About 25 parts by weight of at least one surface modifier or additive.

The present invention also provides an improved composition comprising a number of magnetic particles, at least one surfactant, an organic dispersion medium, and a surface modifier or additive to improve the chemical oxidation of their composition. The present invention relates to a method for producing a magnetic fluid having chemical stability. The process comprises preparing a solvent-based magnetic fluid containing at least one cation, anion or nonionic surfactant adsorbed on the surface of the magnetic particles in the fluid to disperse the particles in a compatible solvent; A low-molecular surface consisting of one of an acid-based additive, an amine-based additive, a silane-based modifier, and a titanium coupling agent to cover exposed portions of the outer layer of magnetic particles that were not previously covered by the agent Adding a modifier or additive, adding a high molecular weight organic dispersion medium, and evaporating the dispersion solvent,
Increasing the temperature of the mixture to disperse the magnetic particles in the dispersion medium.

BEST MODE FOR CARRYING OUT THE INVENTION

The surfactant with a long tail is placed on the magnetic particles, as seen in FIG. However, surfactants with long tails cannot completely cover the entire oxidizable surface of the magnetic particles.

Repeated experiments have shown that organic oils undergo faster oxidation under contact with solid surfaces, especially with oxides. The life of the oil is obviously reduced by mixing the oil with the magnetic particles. Simply calculating, 1 cc of a magnetic fluid with a saturation magnetization of 200 G is 100
It contains about 10 ¹⁶ Angstroms of magnetic particles.
This number of particles is 1 cc of magnetic fluid or 0.7
Provides about 30 m ² of oxidizable surface per cc of oil (0.55 g). This surface area will be greater if the surface of the oxidizable area is not uniform and has topographically "peaks and valleys". Theoretically, due to steric hindrance and geometry, surfactants should be no more than 80-90%
Only oxidizable surfaces could be coated. There is 3-6 m ² of uncovered oxidizable area where very little oil (0.55 g) comes in contact. This simple calculation shows that the effect of the oxidation of most of the oil and surfactant is due to the vast oxide surface due to the uncovered magnetic particle surface.

The present invention uses a surface modifier to cover portions that are not covered by the surfactant used in making the magnetic fluid. The present invention relates to a very low molecular weight, non-dispersant surface that allows entry between the tails of existing surfactants to cover the free surface of particles not covered by the existing surfactants. Requires a modifier.

The surface modifier is very small and small in size so that it can pass between the tails of the surfactant already attached to the magnetic particle surface and enter the uncovered oxidizable surface of the particle. It must be small, its surface must be adsorbed and covered, and its surface must be protected against oxidation.

The surface modifier used in the present invention consists of one to three similar functional groups at one end of the molecule and a very short tail of one to ten atoms. The surface modifier is represented by the following chemical formula. R ¹ _n SiR ² _4-n wherein R ¹ represents a hydrolyzable group selected from the group consisting of alkoxy of 1 to 3 carbon atoms, and R ² represents 1 to 10 carbon atoms. And n is usually 1, 2, or 3. In particular, isobutyltrimethoxysilane was found to be a particularly effective surface treatment agent used in the present invention, and is represented by the above chemical formula, where R ¹ is a methoxy group, R ² is an isobutyl group, and n is 3. The mechanism of attachment to the freely oxidizable surface by silane is that the alkoxy part of the surface modifier
It is considered that silicon reacts with protons from inorganic hydroxyl groups while producing alcohol as a by-product, and silicon binds to oxygen from the aforementioned hydroxyl groups present in the surface layer of the magnetic particles.

During the reaction with the surface, the surface modifier becomes smaller because about one third of the molecules are removed as a by-product of this reaction.

To improve the chemical stability of the ferrofluid, add a suitable amount of antioxidant, choose a good combination of surfactants and oils, substantially uniform, close to 100 Angstroms There are several other methods, such as having a particle size. Despite all these choices being carefully considered, further improvements to ferrofluid chemical oxidation add isobutyltrimethoxysilane or other small molecules with similar ability to cover magnetic particles. Will be achieved by

[0042]

EXAMPLES (Example 1) 13.0 g of ferrous sulfate heptahydrate and 24.0 g of ferric chloride hexahydrate are dissolved in water, and the total solution volume is adjusted to 70 cc with water. Was done. 30 cc of 28% aqueous ammonia was added to the salt iron solution, and Fe ₃ O ₄
Particles settled.

An oleic acid solution consisting of 2.1 g of oleic acid and 27 cc of 3% aqueous ammonia warmed to 70 ° C. was also prepared. The oleic acid solution is then F
was added to a suspension of e ₃ O ₄ particles, the particles were allowed to stand for about 1 hour covered with oleic acid ion. 30 cc of heptane was poured into the suspension of particles covered with oleic acid, and the whole suspension was stirred and left. The particles covered with oleic acid were peptized in heptane, and a magnetic fluid containing heptane as a dispersion medium was placed in a 200 cc beaker.

The magnetite particles covered with oleic acid were agglomerated with 50 cc of acetone, and the supernatant was removed. The particles were washed four times with 50 cc of acetone. 75cc of water and 15cc of 28% ammonia water
Added to the beaker and the particles were suspended by gentle agitation, for example at 60 rpm.

The suspension was heated to 70 ° C., 11 cc of isobutyltrimethoxysilane was added, and the temperature of the suspension was maintained at about 75 ± 5 ° C. for 30 minutes.

After cooling the suspension, the supernatant was removed and the particles were washed five times with 50 cc of acetone.

The washed particles are then dispersed in heptane, 20 cc of 100 ° C., 2 cSt poly-α-olefin oil is added to the heptane-based magnetic fluid, the heptane is removed by heating, and the oil-based magnetic fluid is saturated. The magnetization was adjusted to 200 G by adding oil.

A 200G 2cSt oil-based magnetic fluid,
Sample # 1-1 was obtained. Another ferrofluid based on a 2cSt oil at 200G, Sample # 1-2, was obtained in a similar manner to Sample # 1-1, except that isobutyltrimethoxysilane was not applied to the particles during the process. .

The magnetic fluid samples # 1-1 and # 1-2 were 12.9 mm in inner diameter, 15.0 mm in outer diameter, and 10 mm in height, respectively.
mm glass dishes. The thickness of the magnetic fluid in the glass dish was 3 mm. The glass plate is a perforated aluminum plate (1
(10 mm × 110 mm × 10 mm). The aluminum plate is then heated at a controlled temperature to a mass of aluminum (220 mm × 220 mm × 20 mm) in an oven.
mm). The test was performed at 80 ° C. and the results are shown in Table 1.

[0050]

[Table 1]

Example 2 A heptane-based magnetic fluid covered with oleic acid and treated with isobutyltrimethoxysilane was prepared in the same manner as described in Example 1.

7 cc of polyisobutenyl succinimide and 13 cc of 6 cSt polyalphaolefin oil at 100 ° C. are added to a heptane-based magnetic fluid, where heptane is
Removed by heating, the saturation magnetization of the oil-based magnetic fluid is
It was adjusted to 200 G by adding oil.

A 200G 6cSt oil-based magnetic fluid,
Sample # 2-1 was obtained.

Another magnetic fluid based on a 6 cSt oil at 200 G, Sample # 2-2, was prepared in a similar manner to Sample # 2-1, except that isobutyltrimethoxysilane was not applied to the particles during the process. Made.

The gel time test was performed in the same manner as described in Example 1, but the test temperature was increased to 150 ° C. Table 2 shows the test results.

[0056]

[Table 2]

Example 3 52 g of ferrous sulfate heptahydrate was diluted to about 200 cc with water and stirred until dissolved. To this solution was added 85 cc of 42 Baume iron chloride and stirred until the mixture was homogeneous. About 70cc
Of water and about 125 cc of about 26% ammonium hydroxide was added to the mixed solution and stirred until uniform. The mixture became 60-70 ° C. About 4
A solution of about 50 cc of di-12-hydroxystearic acid in 50 cc of heptane was heated to about 70 ° C. and added to the stirring, warm magnetite mixture. The mixture was then stirred for about 5 minutes. About 350 cc of acetone was added thereto and stirred for about 5 minutes. The mixture was then left to separate for about 1 hour.

The fluid rising to the top was then siphoned off and heated to remove some of the solvent heptane, reducing its volume to about 150 cc.
The fluid was then cooled to room temperature. The fluid is
Collected using about 350 cc of acetone by stirring and placing on a large Alnico V magnet. The supernatant was decanted and the remaining fluid was then finally flocculated and washed twice with 50 cc of acetone. About 1
It was dried twice with 50 cc of acetone to sufficiently remove the acetone. The remaining magnetite was dispersed in about 450 cc of heptane, and the remaining water and acetone were evaporated. The fluid was then filtered through Whatman # 4 filter paper and the dispersing medium trimellitate was added. The solvent was evaporated and the saturation magnetization was adjusted to about 250 G by adding a sufficient amount of trimellitate.

About 0.5 g of sample was weighed into a small glass dish (about 1 cm in diameter x 0.5 cm in height). The dish is placed in a hole drilled in a thick aluminum plate,
Was obtained.

Example 4 52 g of ferrous sulfate heptahydrate was diluted to about 200 cc with water and stirred until dissolved. To this solution was added 85 cc of 42 Baume iron chloride and stirred until the mixture was homogeneous. About 70cc
Of water and about 125 cc of about 26% ammonium hydroxide was added to the mixed solution and stirred until uniform. The mixture became 60-70 ° C. About 4
A solution of about 50 cc of isostearic acid (terminal) di-12-hydroxystearic acid in 50 cc of heptane was heated to about 70 ° C. and added to the stirring warm magnetite mixture. The mixture was then stirred for about 5 minutes. About 350 cc of acetone was added thereto and stirred for about 5 minutes. The mixture was then left to separate for about 1 hour.

The fluid which had risen above was then siphoned off and heated to remove some of the solvent heptane, reducing its volume to about 150 cc.
The fluid was then cooled to room temperature. The fluid is
Collected using about 350 cc of acetone by stirring and placing on a large Alnico V magnet. The supernatant was gently poured out and the remaining magnetite was about 150
resuspended in cc of heptane. This process was repeated four times. The fluid is then finally agglomerated, 50
Washed twice with 2 cc of acetone. Then it is 7
The mixture was washed three times with about 300 cc of a mixture of acetone and water at 0:30. The magnetite was placed in about 600 cc of cold water and stirred vigorously. The pH was adjusted to 9-11 with 26% ammonium hydroxide, followed by the addition of about 6 g of acetic acid. The mixture was stirred for about 30 minutes. The chemical formula of acetic acid is as follows.

[0062]

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The magnetite was collected on an Alnico V magnet and the liquid was sufficiently removed. Then, about 300c
The resultant was washed twice with acetone of c, twice with 70:30 of a mixture of acetone and water, about 300 cc, and finally dried twice with about 300 acetone to remove the liquid sufficiently. The remaining magnetite was dispersed in about 450 cc of heptane, and the remaining water and acetone were evaporated. The fluid is
Then, the mixture was filtered through Whatman # 4 filter paper, and trimellitic acid ester as a dispersion medium was added. The solvent was evaporated and the saturation magnetization was adjusted to about 250 G by adding an additional amount of trimellitate.

About 0.5 g of sample was weighed into a small glass dish (about 1 cm in diameter × 0.5 cm in height). The dish is placed in a hole drilled in a thick aluminum plate,
Was obtained.

Example 5 This example followed the same procedure as Example 4 except that about 15.5 g of allantoin was added instead of acetic acid. The chemical formula of allantoin is as follows:

[0066]

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Example 6 This example followed the same procedure as Example 4 except that about 13.5 g of tripropylamine was added instead of acetic acid. The chemical formula of tripropylamine is as follows.

[0068]

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Example 7 52 g of ferrous sulfate heptahydrate was diluted to about 200 cc with water and stirred until dissolved. To this solution was added 85 cc of 42 Baume iron chloride and stirred until the mixture was homogeneous. About 70cc
Of water and about 125 cc of about 26% ammonium hydroxide was added to the mixed solution and stirred until uniform. The mixture became 60-70 ° C. About 4
A solution of about 50 cc of di-12-hydroxystearic acid in 50 cc of heptane was heated to about 70 ° C. and added to the stirring, warm magnetite mixture. The mixture was then stirred for about 5 minutes. About 350 cc of acetone was added thereto and stirred for about 5 minutes. The mixture was then left to separate for about 1 hour.

The fluid which had risen up was then siphoned off and heated to remove some of the solvent heptane, reducing its volume to about 150 cc.
The fluid was then cooled to room temperature. The fluid is
Collected using about 350 cc of acetone by stirring and placing on a large Alnico V magnet. The supernatant was decanted and the remaining fluid was then finally flocculated and washed twice with 50 cc of acetone. Then it was washed three times with about 300 cc of a 70:30 mixture of acetone and water. And this is about 150
It was dried twice with cc of acetone to sufficiently remove the liquid. The remaining magnetite was dispersed in about 450 cc of heptane, and the remaining water and acetone were evaporated. The fluid is then filtered through Whatman # 4 filter paper,
% Trimellitic acid ester, which is a dispersion medium containing alkyldiphenylamine antioxidant, was added. The solvent is evaporated and the saturation magnetization is reduced to about 2 by adding a sufficient amount of a mixture of trimellitate and antioxidant.
It was adjusted to 50G.

About 0.5 g of sample was measured on a small glass dish (about 1 cm in diameter × 0.5 cm in height). The dish is placed in a hole drilled in a thick aluminum plate,
Was obtained.

Example 8 52 g of ferrous sulfate heptahydrate was diluted to about 200 cc with water and stirred until dissolved. To this solution was added 85 cc of 42 Baume iron chloride and stirred until the mixture was homogeneous. About 70cc
Of water and about 125 cc of about 26% ammonium hydroxide was added to the mixed solution and stirred until uniform. The mixture became 60-70 ° C. About 4
A solution of about 50 cc of di-12-hydroxystearic acid in 50 cc of heptane was heated to about 70 ° C. and added to the stirring, warm magnetite mixture. The mixture was then stirred for about 5 minutes. About 350 cc of acetone was added thereto and stirred for about 5 minutes. The mixture was then left to separate for about 1 hour.

The fluid which had risen up was then siphoned off and heated to remove some of the solvent heptane, reducing its volume to about 150 cc.
The mixture was then cooled to room temperature. The fluid was collected using about 350 cc of acetone by stirring and placing on a large Alnico V magnet. The supernatant was poured out gently and the remaining magnetite was approximately 15
Resuspended again in 0 cc of heptane. This aggregation step is
Repeated four times. The fluid was then finally coalesced and washed with two 50 cc portions of acetone. Then it is a mixture of 70:30 acetone and water, about 300 c
Washed 3 times with c. And the magnetite is about 60
Placed in 0 cc of cold water and stirred vigorously. The pH was adjusted to 9-11 with 26% ammonium hydroxide, followed by addition of about 6 g of acetic acid and stirring for about 30 minutes.

The magnetite was collected on an Alnico V magnet, and the liquid content was sufficiently removed. Then, about 300c
c. twice with acetone, 70:30 mixture of acetone and water, three times with about 300 cc and finally about 300 cc
And dried twice with acetone to sufficiently remove the liquid. The remaining magnetite was dispersed in about 450 cc of heptane, and the remaining water and acetone were evaporated. The fluid was then filtered through Whatman # 4 filter paper. 6
% Trimellitic acid ester, which is a dispersion medium containing alkyldiphenylamine antioxidant, was added. The solvent is evaporated and the saturation magnetization is reduced to about 2 by adding a sufficient amount of a mixture of trimellitate and antioxidant.
It was adjusted to 50G.

About 0.5 g of sample was measured in a small glass dish (about 1 cm in diameter × 0.5 cm in height). The dish is placed in a hole drilled in a thick aluminum plate,
Was obtained.

Example 9 This example followed the same procedure as Example 8 except that about 13.5 g of tripropylamine was added instead of acetic acid.

Example 10 This example was followed except that about 15.0 g of benzoic acid was added instead of acetic acid.
The same steps as in Example 8 were followed. The chemical formula of benzoic acid is as follows.

[0078]

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Example 11 200 g of ferrous sulfate heptahydrate was dissolved in water, and water was added to adjust the total amount of the solution to 840 cc. 370 cc of 42 Baume iron chloride was dissolved in the ferrous sulfate solution. Ammonia water is made by mixing 530 cc of 26% ammonia water with 300 cc of water, and this ammonia water is carefully added to the iron mixed solution to provide about 3
Mix for minutes. The iron mixed solution was pre-warmed to 60 ° C. before adding aqueous ammonia to it. A suspension of 2000 cc of magnetite magnetic particles precipitated.

The above amount of magnetic particles accounts for 26% of 46 cc.
It was mixed with aqueous ammonia. 37 g of oleic acid solution was dissolved in 500 cc of heptane, added to the magnetic particles and stirred for 3 minutes. The whole magnetic particle suspension is 10
Let stand for hours.

The particles covered with oleic acid are peptized in heptane, and the magnetic particles using heptane as a dispersion medium become 100%.
C. and adjusted to 250G.

60 cc of acetone was added to the 40 cc base fluid, the covered magnetic particles aggregated, and the supernatant was removed. The particles were washed three times with 60 cc of acetone.

The washed particles were peptized into 40 cc of heptane, heated to 100 ° C., and 40 cc of Emery 3
004 oil was added. The heptane was evaporated and the particles were suspended in the oil.

Example 12 200 g of ferrous sulfate heptahydrate was dissolved in water, and water was added to adjust the total amount of the solution to 840 cc. 370 cc of 42 Baume iron chloride was dissolved in the ferrous sulfate solution. Ammonia water is made by mixing 530 cc of 26% ammonia water with 300 cc of water, and this ammonia water is carefully added to the iron mixed solution to provide about 3
Mix for minutes. The iron mixed solution was pre-warmed to 60 ° C. before adding aqueous ammonia to it. A suspension of 2000 cc of magnetite magnetic particles precipitated.

The above amount of magnetic particles accounts for 26% of 46 cc.
It was mixed with aqueous ammonia. 37 g of oleic acid solution was dissolved in 500 cc of heptane, added to the magnetic particles and stirred for 3 minutes. The whole magnetic particle suspension is 10
Let stand for hours.

The particles covered with oleic acid are peptized in heptane, and the magnetic particles using heptane as a dispersion medium become 100 particles.
C. and adjusted to 250G.

Then, before mixing the Emery 3004 oil, a solution of 13.5 g of titanium triisostearoyl isopropoxide in 50 cc of heptane was added to the heptane dispersion fluid. The chemical formula of titanium triisostearoyl isopropoxide is as follows.

[0088]

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60 cc of acetone was added to 40 cc of the base fluid, the covered magnetic particles aggregated, and the supernatant was removed. The particles were washed three times with 60 cc of acetone.

The washed particles are peptized into 40 cc of heptane, heated to 100 ° C., and 40 cc of Emery 3
004 oil was added. The heptane was evaporated and the particles were suspended in the oil.

(Embodiment 13) This embodiment is an embodiment of the present invention.
Before mixing the 3004 oil with the heptane-dispersed fluid, instead of titanium triisostearoyl isopropoxide, a solution of 3.8 g of methacryloxypropyltrimethoxysilane in 50 cc of heptane disperses the heptane. Example 12 was followed except that it was added to the medium fluid. The chemical formula of methacryloxypropyltrimethoxysilane is as follows.

[0092]

Embedded image

(Test Data) The thermal stability test was performed for an inner diameter of 13
mm, an outer diameter of 15 mm, and a height of 10 mm. The thickness of the magnetic fluid in the glass dish was about 2 mm. The glass dish was placed on an aluminum plate (250 mm × 250 mm × 10 mm). The aluminum plate was then placed in a temperature controlled oven. The test is performed at 180 ° C.
The results are shown below.

The gel time data is shown in Tables 3, 4 and 5.

[0095]

[Table 3]

[0096]

[Table 4]

[0097]

[Table 5]

As an overview, the present invention relates to a method comprising:
0 parts magnetic particles, 0.1 to about 30 parts of at least one surfactant, 10 to about 99 parts of an organic dispersion medium, and
In order to improve the chemical oxidation stability of the above composition, 0.01
From about 25 parts of at least one surface modifier or additive. What is specified here is the mutual ratio of the volumes of the magnetic particles, the surfactant, the organic dispersion medium, and the surface treatment agent, and other third components may be added in addition to these.

The surfactant is selected from surfactants consisting of a cationic surfactant, an anionic surfactant, and a nonionic surfactant, has a molecular weight of at least 150, and the dispersion medium has a surfactant. Organic molecules that are compatible with the agent.

The present invention also provides an improved composition comprising a number of magnetic particles, at least one surfactant, an organic dispersion medium, and a surface treatment as an additive to improve the chemical oxidation of the described composition. And a method for producing a chemically stable magnetic fluid, the method comprising the following steps.

A solvent-based ferrofluid containing at least one cationic, anionic or nonionic surfactant is prepared. Here, the surfactant is bound to the surface of the magnetic particles in the liquid to disperse the particles in a compatible solvent.

The surfactant adds a low molecular weight surface modifier or additive to cover the exposed surface of the previously uncovered magnetic particles. Additives include acid based additives, amine based additives, silane based modifiers, and titanium coupling agents. The acid-based additive includes acetic acid or benzoic acid. The amine-based additive includes allantoin or tripropylamine. The silane-based surface treatment agent includes methacryloxypropyltrimethoxysilane, and the titanium coupling agent includes titanium triisostearoylisopropoxide. The surface treating agent is represented by the following chemical formula. R ¹ _n SiR ²
_4-n wherein R ¹ represents a hydrolyzable group selected from the group consisting of alkoxy having 1 to 3 carbon atoms, and R ² represents an alkyl group having 1 to 10 carbon atoms. Means and n is usually 1, 2, or 3
It is. Then, a high molecular weight organic dispersion medium is added, the dispersion solvent is evaporated, and the dispersion solvent is evaporated by raising the temperature of the mixture in order to disperse the magnetic particles in the dispersion medium.

[0103]

According to the magnetic fluid composition and the method of manufacturing the same of the present invention, portions of the magnetic particles that are not covered by the surfactant are covered by the surface modifier, so that the magnetic particles can be obtained under different environmental conditions. Thus, better chemical stability of the magnetic fluid can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a magnetic particle on which a surfactant having a long tail is adsorbed.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shiro Tsuda 906-17 Nishiashirai, Asahi City, Chiba Prefecture (72) Inventor Casey Willie Heckman United States 03858 Newton Quaker Street, New Hampshire 9 (72) Inventor Yasuhiro Hirota Hyogo 1209-4 Rokuichi, Inami-cho, Kako-gun F term (reference) 5E041 AB12 BD07 HB14 NN06

Claims (14)

[Claims] 1. A magnetic particle having a volume of 0.1 to 40 parts,
1 to about 30 parts of at least one surfactant,
A chemically stable magnetic fluid comprising about 99 parts of an organic dispersion medium and 0.01 to about 25 parts of at least one surface modifier or additive to improve the chemical oxidative stability of the composition. composition. 2. The magnetic fluid composition of claim 1, wherein the additive comprises one of an acid-based additive and an amine-based additive, and the surface modifier is a silane-based surface treatment agent and a titanium coupling agent. A magnetic fluid composition comprising one of the following. 3. The magnetic fluid composition of claim 2, wherein said acid-based additive is used, and said acid-based additive is acetic acid. 4. The ferrofluid composition of claim 2 wherein said acid-based additive is used and said acid-based additive is benzoic acid. 5. The magnetic fluid composition according to claim 2, wherein the amine-based additive is used, and the amine-based additive is allantoin. 6. The magnetic fluid composition according to claim 2, wherein said amine-based additive is used, and said amine-based additive is tripropylamine. 7. The magnetic fluid composition according to claim 2, wherein the silane-based surface treatment agent is used, and the silane-based surface treatment agent is methacryloxypropyltrimethoxysilane. 8. The magnetic fluid composition according to claim 2, wherein the titanium coupling agent is used, and the titanium coupling agent is titanium triisostearoyl isopropoxide. 9. The magnetic fluid composition according to claim 2, wherein the surface modifier is represented by the following chemical formula and has a concentration of up to 30% by volume. R ¹ _n SiR ² _4-n wherein R ¹ represents a hydrolyzable group selected from the group consisting of alkoxy of 1 to 3 carbon atoms, and R ² represents 1 to 10 carbon atoms. And n is usually 1, 2, or 3. 10. The ferrofluid composition of claim 1, wherein said magnetic particles are ferrite particles having a particle size of about 30 to about 150 angstroms. 11. The magnetic fluid composition according to claim 1, wherein the surfactant is selected from the group consisting of a cationic surfactant, an anionic surfactant, and a nonionic surfactant. The magnetic fluid composition to be used. 12. The ferrofluid composition of claim 1, wherein the surfactant has a molecular weight of at least 150. 13. The magnetic fluid composition of claim 1, wherein the dispersion medium is a surfactant compatible organic molecule and has a concentration between 10 and 95% by volume of the composition. Magnetic fluid composition. 14. A magnetic material with improved chemical stability comprising a number of magnetic particles, at least one surfactant, an organic dispersion medium, a surface treatment or an additive to improve the chemical oxidation of the composition. In the process of making a fluid, the process comprises the following steps: at least one cation, anion, used to bind the magnetic particles surface of the fluid to disperse the magnetic particles in a compatible solvent. Producing a solvent-based ferrofluid containing an ionic or non-ionic surfactant, a low molecular weight surface modifier or additive to cover the exposed portions of the surface layer of the magnetic particles that were not previously covered by the surfactant Wherein the surface modifier or additive comprises one of an acid-based additive, an amine-based additive, a silane-based additive, and a titanium coupling agent. It was added and the organic solvent of high molecular weight, the dispersion solvent was evaporated, to disperse the magnetic particles in a dispersion medium, raising the temperature of the mixture.