KR19980044686A - Method of manufacturing magnetic fluid - Google Patents

Abstract

The present invention relates to a method for modifying a ferromagnetic particle surface, and more particularly, to a method for producing a magnetic fluid in which a ferromagnetic material is stably dispersed in a high boiling point organic solvent by thermal dehydration of a surfactant on a ferromagnetic particle surface.

In the present invention, the silane coupling agent is first bonded to the ferromagnetic fine particles. The silane coupling agent and the surfactant are then heat-condensed to the ferromagnetic fine particles to form chemical bonds. Next, the high-boiling magnetic fluid is produced by dispersing ferromagnetic fine particles combined with a surfactant in a high-boiling organic solvent.

The magnetic fluid produced in this way is a colloidal solution in which ferromagnetic ultra-fine particles are very stably dispersed in the fluid. Even though a large amount of centrifugal force or magnetic field is applied to the fluid, the particles are not separated from the fluid. As a result, the magnetic fluid is a liquid having magnetic properties in the magnetic field. It acts as.

Description

Method of manufacturing magnetic fluid

The present invention relates to a method of modifying a ferromagnetic particulate surface, and more particularly, to a method of producing a magnetic fluid in which a ferromagnetic substance is stably dispersed in a high boiling organic solvent by thermal dehydration of a surfactant on a ferromagnetic particulate surface.

One method of producing a magnetic fluid is known to use a surfactant, in which the surface of the ferromagnetic particles is coated with a surfactant. The hydrophilic group of the surfactant is then adsorbed toward the surface of the ferromagnetic fine particles, the hydrophobic groups are oriented in the dispersion medium, and the ferromagnetic fine particles are stably dispersed in the dispersion medium. That is, Fe ²⁺ and Fe ³⁺ are reacted with 8NH ₄ OH to obtain Fe ₃ O ₄ as shown in the following Reaction Formula 1, and then oleic acid as a surfactant is adsorbed thereon, and then dispersed in mineral oil, which is a high boiling point organic solvent. It is a method for producing a magnetic fluid.

[Scheme 1]

However, since the magnetic fluid composition prepared by this method has a weak electrostatic interaction between the surface of the surfactant and the ferromagnetic particles, the adsorption effect of external factors such as the influence of heat, the incorporation of a polar solvent, or the application of an external voltage. Since the surfactant is separated and sedimented from the ferromagnetic particles, it is difficult to maintain long-term stability.

In another prior art, a method of producing a magnetic fluid using a silane coupling agent is known. This method chemically bonds the ferromagnetic fine particles with the silane coupling agent by dehydrating the OH group and the silanol group of the silane coupling agent on the surface of the ferromagnetic particles produced by the wet method. And a silane chemically bonded to the -OH group on the surface of the ferromagnetic particle by treating a ferromagnetic fine particle chemically bonded with a silane coupling agent and a single-terminal reactive silicone oil having an epoxy group at one end and a low boiling point dimethylpolysiloxane as a dispersion medium in a ball mill. The amino group of the coupling agent is reacted with an epoxy group at one terminal reactive silicone oil terminal. Next, the low boiling point dimethylpolysiloxane is removed by evaporating the particles having poor dispersibility, and the dried particles are dispersed in the high viscosity dimethylpolysiloxane to prepare a magnetic fluid.

However, there is a problem in that it takes a long time to prepare a magnetic fluid by using a ball mill to chemically bond the surfactant to the magnetic powder treated with the silane coupling agent.

An object of the present invention is to provide a magnetic fluid in which ferromagnetic particles dispersed in a high boiling organic solvent have long-term dispersion stability.

Another object of the present invention is to provide a method for manufacturing a magnetic fluid having low manufacturing cost and shortening manufacturing time.

According to the present invention, a method of producing a magnetic fluid in which the ferromagnetic particles are stably dispersed in a high boiling organic solvent is provided by surfactant dehydration on the surface of the ferromagnetic particles using a silane coupling agent.

The present invention relates to a ferromagnetic material reacted with a ferromagnetic fine particle produced by a wet method, a coupling agent having a reactor that chemically bonds directly to the ferromagnetic particle surface, and a surfactant having a reactor capable of directly chemically bonding the other coupling agent of the coupling agent. A method of producing a magnetic fluid in which fine particles are dispersed in a high boiling organic solvent, wherein the silane coupling agent is bonded to the ferromagnetic fine particles, and other reactors and surfactants of the silane coupling agent combined with the ferromagnetic fine particles are dehydrated while being heated in the presence of a low boiling organic solvent. And a step of condensing and dispersing the ferromagnetic fine particles combined with a surfactant in a high boiling point organic solvent.

The present invention will be described in detail as follows.

The silane coupling agent used in the present invention has a structure of XSi (OR) ₃ , X is a reactor that chemically bonds with organic materials such as various synthetic resins, vinyl group, epoxy group, amino group, methacryl group, mepcafuto group is applied OR may be a methoxy group, ethoxy group, etc. may be applied as a reactor chemically bonded to inorganic materials such as glass metal. Looking at the reactor of the silane coupling agent having the above structure, first, the alkoxysilyl group (Si-OR) of the silane coupling agent is hydrolyzed by water or moisture to become a silanol group (Si-OH). On the other hand, the ferromagnetic fine particles produced by the wet method have a -OH group on the surface. Dehydration and condensation reaction occurs in the OH period of the silanol group of the silane coupling agent formed by hydrolysis and the surface of the ferromagnetic fine particles, thereby forming Si-OM bonds. Thus, the silane coupling agent is chemically firmly fixed to the surface of the ferromagnetic particulate. On the other hand, another reactor (X) of the silane coupling agent bonded to the ferromagnetic particles is a reactor capable of chemically bonding organic materials such as various synthetic resins. As such, one reactor (OR) of the silane coupling agent is combined with a surfactant, which is an organic material, and the other reactor (X), is combined with ferromagnetic particles, which are inorganic materials. That is, the silane coupling agent plays an intermediate role in chemically bonding the ferromagnetic particulates and the surfactant.

In the present invention, a method of heating and dehydrating a surfactant is used to prepare a magnetic fluid. First, the hydroxyl group (-OH) on the surface of the ferromagnetic ultrafine particles prepared by the wet method and the silanol group of the silane capping agent are dehydrogenated to form Si-OM bonds. Thus, when a surfactant having a carboxyl group (-COOH) is heated to about 160 ° C in the presence of xylene, the reactor of the silane capping agent that is oriented outward of the ferromagnetic particles ( The carboxyl group, which is a reactor of X) and a surfactant, is dehydrated to form a chemical bond. Here, as the surfactant having a carboxyl group as a reactor, oleic acid (C ₁₇ H ₃₃ COOH), stearic acid (C ₁₇ H ₃₅ COOH) and the like are used. In this manner, a reaction represented by the following Scheme 2 was formed, and the organic surfactant was stably bonded to the surface of the ferromagnetic particles. Then, decantation is performed after placing the magnet on the heat-condensed reactant to remove non-dispersed solids. The xylene base magnetic fluid thus prepared is added to the high boiling organic solvent and then heated to evaporate xylene, which is a low boiling organic solvent. Thus, the magnetic fluid suitable for the purpose of the present invention is prepared by dispersing ferromagnetic fine particles in which inorganic and organic chemically bonded to a high boiling point organic solvent.

[Scheme 2]

Here, M is a ferromagnetic fine particle, and corresponds to the R'-NH ₂ reactor X in the above Reaction Scheme 2, R 'is a hydrocarbon chain, in particular a linear or branched aliphatic hydrocarbon having 1 to 3 carbon atoms.

As the silane coupling agent of the present invention, N-β (Amino ethyl) γ-Amino propyl methyl dimethoxy silane having an amino group in the reactor (X), N-β (Amino ethyl) γ-Amino propyl trimethoxy silane, N-β (Amino ethyl) One or more selected from among γ-Amino propyl triethoxy silane, γ-Amino propyl trimethoxy silane, and γ-Amino propyl trimethoxy silane can be used together.

The addition amount of the coupling agent of the present invention is optimally the amount that completely covers the surface of the ferromagnetic particulate with a monomolecular film, and can be calculated by the following equation (1).

[Equation 1]

Here, the minimum cross-sectional area of the silane coupling agent is 13 kPa in area per molecule. Therefore, the area per 1 g is determined by "13 Pa x Avogadr number (6.02 x 10 ²³ ) / molecular weight".

As the magnetic particles, ferromagnetic particles are preferable. Specifically, one or more mixtures selected from oxide magnetic particles such as magnetite, Mn-Zn ferrite, cobalt ferrite and barium ferrite, magnetic metal particles such as iron and cobalt, and iron nitride particles are used. Good to do. In particular, in consideration of the reactivity with the silane coupling agent, the oxide magnetic particles having a large number of hydroxyl groups on the surface is preferred, the magnetite particles are preferred considering the ease of manufacture.

The particle diameter of the magnetic particles is preferably 3 nm to 500 nm, preferably 10 nm to 100 nm. When the particle diameter of the magnetic particles exceeds 500 nm, the dispersibility becomes poor, and the particles precipitate. When the particle size falls below 3 nm, the particles do not exhibit magnetic properties.

As a high boiling point organic solvent, boiling point is 150-700 degreeC at normal pressure, Preferably it is 200-600 degreeC, More preferably, it is 300-600 degreeC. For example, mineral oil solvents such as kerosene, light oil increments and lubricating oil increments, synthetic hydrocarbons such as normal paraffins, isoparaffins, alkylbenzenes, alkylnaphthalenes and polyalphaolefins, ethers such as polyalkylene oxides, polyglycols and polyphenylethers. Ester solvents, such as esters, polyol esters, diesters, and monoesters, fluorinated hydrocarbons, and silicones, can be used.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

150 ml of FeSO ₄ · 7H ₂ O and FeCl ₃ · 6H ₂ O of the reagent grade having an initial concentration of Fe ²⁺ of 0.9 mole / L and a Fe ²⁺ / Fe ³⁺ ratio of 5/6 were prepared, respectively. And mixed in a 1 L beaker. While stirring the iron salt solution vigorously with a mechanical stirrer, NH ₄ OH, a neutralizing agent was added, and the pH before and after the reaction was constant at 9 to 9.5 to obtain a magnetite suspension. In order to remove the salt of the obtained magnetite suspension, after the magnetite was precipitated, the supernatant was removed, and again, ion exchanged water was added, and the supernatant was removed. In this way, the electrolyte in the slurry was removed. The above is the process of manufacturing a magnetite colloid by a wet method.

Next, an aqueous solution of 9.47 g of N-β (Amino ethyl) γ-Amino propyl trimethoxy silane, an amount capable of completely covering the surface of the ferromagnetic particles, was added to the magnetite water slurry containing about 23.9 g of magnetite as an aqueous solution. The silane coupling agent was made to adsorb | suck the surface of magnetite microparticles | fine-particles by stirring liquid temperature at 60 degreeC for 30 minutes. This was left to stand and the magnetite particles in the liquid were flocculated and precipitated. Thereafter, the mixture was washed with water and vacuum-dried for 3 hours in a vacuum dryer to obtain powdery magnetite fine particles whose surface was coated with a silane coupling agent.

Into a 1L beaker, dried fine particles treated with a silane coupling agent, 100 ml of ion-exchanged water, and 12.0 g of olefinic acid were added, followed by ultrasonic waves for 10 minutes. The contents of the beaker are then stirred with a mechanical stirrer. The heat condensation reaction was carried out by maintaining the solution temperature at 160 ° C. for 2 hours. The xylene base magnetic fluid having completed the heat condensation reaction was temporarily left in the magnet, and then decantation was performed to obtain a xylene base magnetic fluid from which non-dispersed solids were removed. The prepared xylene base magnetic fluid was added to an oil mixed with spindle oil (Meropa 220, Honam essential oil) and marinized polybutene (HV-100M, Nippon Chemical Chemical Co., Ltd.) at 8.8: 1.2, and the high boiling point was obtained by evaporating xylene. Magnetic fluid was prepared. The prepared magnetic fluid had a saturation magnetization of 100 G and a viscosity of 1,000 to 10,000 cP.

Example 2

Magnetic fluid was prepared in the same manner as in Example 1 using γ-Amino propyl trimethoxy silane as a silane coupling agent.

The magnetic fluid thus prepared also showed the same thermal characteristics as in Example 1.

Example 3

The dried fine particles treated with the silane capping agent obtained in Example 1, 100 ml of xylene, and 12.17 g of stearic acid were placed in a 1 L beaker, and then ultrasonic waves were added for 10 minutes. The contents of the beaker are then stirred with a mechanical stirrer. The heat condensation reaction was carried out by maintaining the solution temperature at 160 ° C. for 2 hours. The xylene base magnetic fluid having completed the heat condensation reaction was temporarily left in the magnet, and then decantation was performed to obtain a xylene base magnetic fluid from which non-dispersed solids were removed. The prepared xylene base magnetic fluid was added to an oil mixed with spindle oil (Meropa 220, Honam essential oil) and marinized polybutene (HV-100M, Nippon Chemical Chemical Co., Ltd.) at 8.8: 1.2, and the high boiling point was obtained by evaporating xylene. Magnetic fluid was prepared.

The magnetic fluid thus prepared also showed the same thermal characteristics as in Example 1.

According to the present invention, a magnetic fluid having a long-term dispersion stability can be produced by using a silane coupling agent to chemically bond a surfactant to the ferromagnetic fine particles and disperse the magnetic powder in a high boiling organic solvent. Therefore, the magnetic fluid is a colloidal solution in which the ferromagnetic ultra-fine particles in the fluid are dispersed very stably. Even though a considerable centrifugal force or magnetic field is applied to the fluid, the particles are not separated from the fluid. As a result, the magnetic fluid is a liquid having magnetic properties in the magnetic field. Behaves.

In addition, in order to chemically bind the surfactant to the powder treated with the silane coupling agent, a magnetic fluid was prepared by using a ball mill for a long time, but magnetic fluid was prepared according to the method. Because of the interfacial polycondensation method, the magnetic fluid can be produced in a short time, and the manufacturing cost is low because of the low man-hours.

Furthermore, there is also an advantage in that non-dispersed solids can be easily removed by using xylene as an intermediate step in the preparation of the magnetic fluid.

Claims (4)

A high boiling point organic solvent is prepared by reacting ferromagnetic particles produced by the wet method with a coupling agent having a reactor capable of chemically bonding the ferromagnetic particles directly to the surface of the ferromagnetic particles, and a surfactant having a reactor capable of directly chemically bonding other reactors of the coupling agent. In the magnetic fluid manufacturing method to be dispersed in, Silane coupling agent is bonded to the ferromagnetic particles; Dehydrating and condensing the other reactor and the surfactant of the silane capping agent combined with the ferromagnetic particles while being heated in the presence of a low boiling organic solvent; And dispersing the ferromagnetic particles in which the surfactant is bound in a high boiling organic solvent. The method of producing a magnetic fluid according to claim 1, wherein as the surfactant, oleic acid having a carboxyl group (C ₁₇ H ₃₃ COOH), stearic acid (C ₁₇ H ₃₅ COOH), or the like is used as the reactor. The method according to claim 1, wherein the general formula of the silane coupling agent is XSi (OR) ₃ (X: a reactor capable of chemically bonding with an organic material, at least one of a vinyl group, an epoxy group, an amino group, a methacryl group, a mercaputo group, OR: A reactor capable of chemically bonding with an inorganic material is a method for producing a magnetic fluid, characterized in that at least one of a methoxy group, an ethoxy group). The silane coupling agent having an amino group as a reactor according to claim 1, wherein N-β (Amino ethyl) γ-Amino propyl methyl dimethoxy silane, N-β (Amino ethyl) γ-Amino propyl trimethoxy silane, N- Magnetic fluid characterized by using one or more selected from β (Amino ethyl) γ-Amino propyl triethoxy silane, γ-Amino propyl trimethoxy silane, γ-Amino propyl triethoxy silane, N-phenyl γ-amino propyl trimethoxy silane Manufacturing method.