JPH0223602A - Water-based magnetic fluid composition and method for its production - Google Patents

Abstract

PURPOSE:To maintain the excellent state of dispersion for a prolonged term by chemically bonding a coupling agent having a hydrophilic group and at least one hydrolyzable group with the surfaces of ferromagnetic substance particulates through the reaction product of the hydrolyzable group. CONSTITUTION:The surfaces of ferromagnetic substance particulates being a dispersoid have a hydroxyl group. A hydrolyzable group on one end side of the molecule of a coupling agent is, on the contrary, hydrolyzed in water and the hydroxyl group is generated. A dehydration condensation reaction is generated between the hydroxyl group formed by the hydrolysis and the hydroxyl group on the surfaces of the ferromagnetic substance particulates. Consequently, the coupling agent is chemically bonded firmly with the surfaces of particulates while hydrophilic groups at a reverse end are directed toward the outside and cover the surfaces of the particulates. Accordingly, the ferromagnetic substance particulates are dispersed into water as a dispersion medium extremely stably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a water-Heath magnetic fluid composition in which ferromagnetic fine particles are stably dispersed in water as a dispersion medium via a dispersant, and a method for producing the same. Regarding, especially using hydrolysis reaction,
By chemically bonding a dispersant to the surface of ferromagnetic particles, we provide a highly stable water-based ferrofluid composition and an efficient method for producing the same.

[Prior art] As a conventional magnetic fluid using water as a dispersion medium,
,! There is one described in the -40069 publication. In this method, a monomolecular adsorption layer of a surfactant (first surfactant) whose main component is an unsaturated fatty acid or its salt is first applied in an aqueous phase to the surface of a fine ferromagnetic oxide powder obtained by a wet method. After the formation, an anionic or nonionic surfactant (second surfactant) is oriented and adsorbed in the second layer to stably disperse the ferromagnetic particles in water. The base magnetic fluid is obtained.

[Problem to be solved by the invention]

However, the conventional magnetic fluid using water as a dispersion medium has various problems as described below.

■ The adsorption of the second surfactant is physical adsorption with a very weak adsorption force, and is easily desorbed (based on van der Waals forces due to interaction between lipophilic groups with the first surfactant). It is difficult to maintain stable dispersion of ferromagnetic particles over a long period of time.

■ Since the solubility of the second surfactant in water changes due to temperature changes, the equilibrium between the excess of the second surfactant present in the bulk and the amount adsorbed in the second layer changes with temperature. Much depends. That is, the second surfactant may be desorbed due to a change in temperature, and the dispersion stability of the ferromagnetic fine particles may deteriorate.

(2) The magnetic fluid itself easily foams due to the excessive amount of the second surfactant present in the water, making it difficult to handle.

■ When a small amount of oil or polar solvent mixes with the magnetic fluid,
Desorption occurs of the surfactant adsorbed on the second layer and furthermore on the surfactant adsorbed on the -layer. As a result, the dispersed ferromagnetic fine particles may settle, or the magnetic fluid itself may become emulsified.

The present invention was made by focusing on such conventional problems, and uses a force/knobbling agent having at least one hydrolyzable group as well as a hydrophilic group as a surfactant.
By chemically bonding the coupling agent to the surface of the ferromagnetic fine particles through the reaction product of the hydrolyzable group and water, coupling is achieved that does not easily attach or detach from the surface of the ferromagnetic fine particles, which are inherently hydrophilic. The purpose of the present invention is to solve the above-mentioned conventional problems by coating it with an agent and dispersing it in water more stably.

[Means to solve the problem]

The water-Heath magnetic fluid composition of the present invention, which achieves the above object, has a water-Heath magnetic fluid composition in which water is used as a dispersion medium and ferromagnetic fine particles are used as a dispersoid.
A coupling agent having a hydrolyzable group is chemically bonded to the surface of the ferromagnetic fine particles via a reaction product of the hydrolyzable group.

The hydrolyzable group of the coupling agent is preferably an alkoxy group.

Further, the method for producing a water-based magnetic fluid of the present invention includes adding water and a coupling agent having at least one hydrolyzable group in addition to a hydrophilic group to ferromagnetic fine particles to form a hydrolyzable group. Hydrolyzing and chemically bonding the coupling agent to the surface of the ferromagnetic particles via the reaction product, thereby obtaining an intermediate medium in which the ferromagnetic particles are uniformly dispersed in an aqueous dispersion medium; This method includes the steps of separating ferromagnetic fine particles with poor dispersibility in the intermediate medium, and then evaporating and separating the by-product of the hydrolysis reaction and at least a portion of the water.

Furthermore, the ferromagnetic fine particles have at least one hydrolyzable group in addition to water and a hydrophilic group, and the surface of the ferromagnetic fine particles is chemically bonded to the surface of the ferromagnetic fine particles through a reaction product of the hydrolyzable group. A step of adding a coupling agent to be bonded and immediately thereafter heating above the boiling point of water to obtain ferromagnetic fine particles whose surfaces are coated with the coupling agent; and adding water to the ferromagnetic fine particles to form a mixture. The method may include a step of separating ferromagnetic fine particles having poor dispersibility from the mixture.

[Effect]

The ferromagnetic fine particles, which are dispersoids, have 10H groups on their surfaces. On the other hand, in a coupling agent, the hydrolyzable group at one end of the molecule is hydrolyzed in water to form 10 H
give rise to a group. A dehydration condensation reaction occurs between the 10H groups generated by this hydrolysis and the 10H groups on the surface of the ferromagnetic fine particles. As a result, the coupling agent is strongly chemically bonded to the particle surface and covers the particle surface with the hydrophilic group at the opposite end facing outward. As a result, the ferromagnetic fine particles are extremely stably dispersed in water, which is a dispersion medium.

Hereinafter, the magnetic fluid composition of the present invention and its manufacturing method will be explained in detail.

The dispersant for ferromagnetic fine particles of the present invention is different from conventional surfactants, which contain a polar group that acts as a hydrophilic group and a non-polar group that acts as a lipophilic group (hydrophobic group) in the structure. The way they are combined with each other and their mechanism of action are different.

That is, the dispersant of the present invention has the general formula YR3iX, for example.
A silane cup represented by ++ is used. In the formula, rr=1 to 3, X is a hydrolyzable group consisting of an alkoxy group such as a methoxy group (CH30-) or an ethoxy group (C2H5O-), R is an ethylenediamine or other hydrocarbon chain, and Y is a carboxylic acid It is a hydrophilic group consisting of basic salts, quaternary ammonium salts, isothiouronium salts, etc. However, the hydrophilic group may be anionic, cationic, or nonionic, and the number thereof may be one or more.

Specifically, as such a silane coupling agent,
For example, the following are preferred.

■ N-[(3i-rimethoxysilyl)propyl]ethylenediaminetriacetic acid sodium salt＼ 5i(OCHs)s ■ Trimethoxysilylpropylisothiouroni＼ CH2CH251(OCH3)s ■ N-trimethoxysilylpropyl tri-N-butylammonium pro Ride CH2N″B U3B r / H3 \ CHzSi(○Me): + The above silane coupling agent has a structure in which the alkoxy group YR3i
(OH) It becomes n. - The ferromagnetic fine particles M have 10H groups on their surfaces (M-OH). Therefore, a dehydration condensation reaction occurs between the two, resulting in a metasiloxane bond (
It is thought that they are chemically bonded by Si-0-M).

The optimum amount of the coupling agent added as a dispersant of the present invention is such that the surface of the ferromagnetic fine particles is completely covered with a monomolecular film. It can be calculated from the surface area of the ferromagnetic fine particles using the following formula.

Amount of coupling agent added - (Weight of ferromagnetic fine particles Covered area per 13 people 2
Therefore, per gram is (13 people 2 x 6.02
x 1023)/determined from the molecular weight. Here 6.
02X1023 is Avogadro's number.

In the actual process, an appropriate amount of silane coupling agent is added to the ferromagnetic particles, taking into account the specific surface area water content of the ferromagnetic particles, the hydrolyzability of silane, and the lls% formation state. Then, increase or decrease the amount added after checking the processing conditions.

As the ferromagnetic fine particles of the present invention, those obtained as a colloidal aqueous suspension (slurry) by a well-known wet method may be used. The wet method here refers to adding an alkali to an acidic solution containing ferrous ions and ferric ions in a ratio of 1=2, adjusting the pH to about 9 or higher, and aging it at an appropriate temperature to obtain magnetite colloid. It is something. Also,
It may be obtained by a so-called wet pulverization method in which magnetite powder is pulverized in a ball mill in water or an organic solvent. Furthermore, other materials obtained by a dry method may also be used.

In addition to magnetite, ferromagnetic fine particles such as manganese ferrite, nickel ferrite, cobalt ferrite, composite ferrite of these and zinc, and barium ferrite, and ferromagnetic metal fine particles such as iron and cobalt can also be used.

The content of ferromagnetic fine particles is not only in the range of 1 to 20% by volume, which is conventionally used for boat fishing, but also in the range of 1 to 20% by volume, which is conventionally used for boat fishing. It also becomes possible to adjust to a high concentration.

In the process of the present invention, first, water and the above coupling agent are added to ferromagnetic fine particles to hydrolyze the hydrolyzable groups, and the coupling agent is transferred to the ferromagnetic fine particles through the reaction product. chemically bond to the surface of the material to obtain an intermediate medium. Next, the poorly dispersible particles in this intermediate medium are centrifuged, and then the water in the intermediate medium and the alcohol, which is a hydrolysis product, are removed under reduced pressure and once dried, and water as a dispersion medium is added thereto. to obtain a water-based ferrofluid of a predetermined concentration.

Alternatively, a water-based magnetic fluid concentrated to a predetermined concentration may be obtained by heating the centrifuged intermediate medium under reduced pressure to evaporate the hydrolyzed alcohol and a portion of the water.

Alternatively, before applying the intermediate medium to a centrifuge, heat it under reduced pressure to dry it, then add water to the dried particles to make a dispersion solution, then apply it to a centrifuge to remove particles with poor dispersibility. It may be separated and removed. In order to obtain a water-based magnetic fluid with an even higher concentration, particles with poor dispersibility may be separated and removed as described above, and after drying again, a predetermined amount of water may be added to obtain a highly concentrated one. Alternatively, a highly concentrated water-based magnetic fluid may be obtained by heating and concentrating without drying.

In this way, the coupling agent binds metasiloxane with its alkoxy group to the surface of the ferromagnetic fine particles, and coats the surface of the ferromagnetic particles in a single layer with the hydrophilic groups facing outward, resulting in a water-based magnetic fluid. , a detailed description of the invention.

[Example 1] First, ferrous sulfate and ferric sulfate were mixed with Q and 3, respectively.
1 jl of aqueous solution containing m o A! , 6N NaO
After adding Haq until the pH reached 11 or higher, the solution was aged at 60°C for 30 minutes to obtain a slurry liquid of magnetite colloid. Then, the electrolyte in this slurry is removed by washing with water at room temperature. The above is a process for producing magnetite colloid by a wet method. The magnetite colloid liquid thus obtained was centrifuged to recover only magnetite, which was dried under reduced pressure at 80°C for 3 hours.

To 5.0 g of the dried magnetite fine particles, 3.0 g of silane coupling agent N-[(3trimethoxysilyl)propyl]ethylenediamine sodium acetate was added as a dispersant.
0 g and 12.0 g of water were added, and pulverization and dispersion operations were performed for 4 hours using a ball mill. In this way, an intermediate medium was obtained in which fine magnetite particles whose surfaces were coated with the silane/knobling agent were stably dispersed in water.

This intermediate medium is centrifuged and treated under a centrifugal force of 8000 G for 30 minutes to sediment and remove particles with relatively large diameters and poor dispersibility among the magnetite dispersed particles. Next, the clear liquid in which the fine magnetite particles that remained without settling are suspended is transferred to a rotary evaporator and kept at 50°C to evaporate and remove methanol and water produced by hydrolysis of the silane coupling agent.

Further, the product was dried under reduced pressure at 80'C to remove water by evaporation, thereby obtaining fine magnetite particles coated with a silane coupling agent. Next, 8Qwt% of water was added to the magnetite fine particles to redisperse them in water.

This was further centrifuged and processed under a centrifugal force of 8000G for 30 minutes. By this centrifugation operation, undispersed solids were removed, and the colloidal liquid above was an extremely stable magnetic fluid.

[Example 2] Magnetite colloid was produced by a wet method in the same manner as in Example 1 above, and further dried under reduced pressure. To 8.0 g of the dried magnetite fine particles, 7.6 g of trimexysilylpropylisothiouronium chloride as a silane coupling agent and 12.0 g of water were added, and pulverization and dispersion were performed using a ball mill for 4 hours. In this way,
An intermediate medium was obtained in which fine magnetite particles whose surfaces were coated with the above silane coupling agent were stably dispersed in water.

Next, transfer this intermediate medium to a rotary evaporator,
The temperature is maintained at 90°C to remove methanol and water produced by hydrolysis of the silane coupling agent by evaporation.

After that, 20g of water was added to this to re-disperse it, which was then placed in a centrifuge and processed under a centrifugal force of 8000G for 30 minutes to precipitate the relatively large particles with poor dispersibility among the magnetite dispersed particles. At least remove it.

The obtained magnetic fluid was extremely stable.

〔Effect of the invention〕

According to the present invention, in order to stably disperse a ferromagnetic material in a water-based dispersion medium, the dispersant has a hydrophilic group at one end of its molecular structure and a hydrolyzable group at the other end. A coupling agent having a group was used to form a chemical bond to the surface of ferromagnetic fine particles via a reaction product of a hydrolyzable group of the coupling agent. Therefore, unlike conventional methods in which the dispersant simply physically adsorbs to the surface of the ferromagnetic particles,
Even if there is a temperature change, a polar solvent is mixed in, or a small amount of foreign matter such as oil is mixed in, the material is not easily desorbed and maintains a good dispersion state for a long period of time.

In addition, since the amount of dispersant added is such that a monomolecular layer is formed on the surface of the ferromagnetic fine particles, the ferromagnetic fluid itself is easily disintegrated by the surfactant present in excess in water, unlike conventional methods. The phenomenon of foaming is prevented and handling becomes easier.

Claims (4)

[Claims] (1) In a water-based magnetic fluid composition in which water is used as a dispersion medium and ferromagnetic fine particles are used as a dispersoid, a coupling agent having a hydrophilic group and at least one hydrolyzable group is added to the hydrolyzable group. A water-based magnetic fluid composition, characterized in that the water-based magnetic fluid composition is chemically bonded to the surface of the ferromagnetic fine particles via a reaction product of the above. (2) The water-based magnetic fluid composition according to claim 1, wherein the hydrolyzable group of the coupling agent is an alkoxy group. (3) Water and a coupling agent having at least one hydrolyzable group in addition to a hydrophilic group are added to the ferromagnetic fine particles to hydrolyze the hydrolyzable group, and the reaction product is A step of chemically bonding the coupling agent to the surface of the ferromagnetic particles to obtain an intermediate medium in which the ferromagnetic particles are uniformly dispersed in an aqueous dispersion medium; A method for producing a water-based magnetic fluid composition comprising the steps of separating body particulates and then evaporating and separating a by-product of the hydrolysis reaction and at least a portion of the water. (4) The ferromagnetic fine particles have at least one hydrolyzable group in addition to water and a hydrophilic group, and the surface of the ferromagnetic fine particles is chemically bonded to the surface of the ferromagnetic fine particles through the reaction product of the hydrolyzable group. A step of adding a coupling agent to be bonded and immediately thereafter heating above the boiling point of water to obtain ferromagnetic fine particles whose surfaces are coated with the coupling agent; and adding water to the ferromagnetic fine particles to form a mixture. A method for producing a water-based magnetic fluid composition, comprising the steps of: separating ferromagnetic fine particles having poor dispersibility from the mixture.