JPH0661032A - Water base magnetic fluid composition - Google Patents

Abstract

PURPOSE:To obtain a water base magnetic fluid composition, which is low in cost and has a stable dispersibility for a long term, by a method wherein a water-soluble polymer is used as a dispersant. CONSTITUTION:A low-cost water-soluble polymer 10 is used as a dispersant for making ferromagnetic material fine particles 1 disperse in water 11 of a dispersion medium. A high dispersibility and a superior dispersion stability are obtained by the synergistic effect of the strong static repulsion action of the polymer 10 and a steric hindrance action.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based magnetic fluid composition in which ferromagnetic fine particles are stably dispersed in water as a dispersion medium through a dispersant, and in particular, a water-soluble polymer is used as the dispersant. It is inexpensive, and can obtain extremely stable dispersibility over a long period of time.

[0002]

2. Description of the Related Art Conventional magnetic fluids containing water as a dispersion medium include, for example, those described in Japanese Patent Publication No. 54-40069 and Japanese Patent Application Laid-Open No. 2-23602. The former one is, as schematically shown in FIG. 2, on the surface of the ferromagnetic fine particles 1 obtained by the wet method, first, in a water phase, a surfactant containing an unsaturated fatty acid or a salt thereof as a main component (first After forming a monomolecular adsorption layer of 2), anionic or nonionic surfactant (2nd surfactant) 3 is orientated and adsorbed on the second layer to obtain ferromagnetic properties. By stably dispersing the body particles 1 in water,
A water-based magnetic fluid is obtained.

On the other hand, the latter, as shown in FIG.
A coupling agent 5 having a salt type hydrophilic group 4 and at least one hydrolyzable group is used as a dispersant, and the surface of the ferromagnetic fine particles 1 is chemically bonded through a reaction product 6 of the hydrolyzable group. The ferromagnetic fine particles 1 are bound to each other and stably dispersed in water by the salt-type hydrophilic groups 4 oriented to the water side which is a dispersion medium to obtain a water-based magnetic fluid.

[0004]

However, the above-mentioned conventional magnetic fluid using water as a dispersion medium has various problems as described below. That is, Japanese Examined Patent Publication No. 54-40069
Regarding the one disclosed in the publication, the adsorption of the second surfactant is a physical adsorption having a very weak adsorptive force, and the (Van der Waals by the interaction of the lipophilic groups with the first surfactant is described. It is easy to be desorbed (based on force), and it is difficult to maintain stable dispersion of the ferromagnetic fine particles for a long period of time. Since the solubility of the second surfactant in water changes due to the temperature change, the equilibrium between the excess amount of the second surfactant present in the bulk and the adsorbed amount in the second layer is large in temperature. Dependent. That is, the second surfactant may be desorbed due to the change in temperature, and the dispersion stability of the ferromagnetic fine particles may be deteriorated. It is difficult to handle because the magnetic fluid itself easily foams due to the second surfactant that is excessively present in water. By mixing a small amount of oil or polar solvent into the magnetic fluid,
Desorption of the surfactant adsorbed on the second layer and further the surfactant adsorbed on the first layer occurs. As a result, the dispersed ferromagnetic fine particles may be precipitated or the magnetic fluid itself may be emulsified.

On the other hand, the one disclosed in Japanese Patent Application Laid-Open No. 2-23602 is improved by focusing on the problems (1) to (3) disclosed in the above Japanese Patent Publication No. 54-40069. Was unresolved. (A) Alcohol is produced as a by-product when the hydrolyzable group (alkoxy group) of the coupling agent, which is a dispersant, undergoes a coupling reaction with the surface of the ferrofluid fine particles, and it is necessary to remove it. is there. (B) Since the molecular weight of the coupling agent is relatively small (M
(Less than W1000), the three-dimensional protective action of suspending the ferromagnetic fine particles themselves in water to prevent aggregation is not so great. Therefore, long-term dispersion stability is not sufficient. (C) The coupling agent having a salt type hydrophilic group is a special chemical and is very expensive, and there is a problem in terms of economy as a magnetic fluid dispersant.

Therefore, the present invention has been made in view of such conventional problems, and uses a water-soluble polymer having a large number of salt-type hydrophilic groups in the chain length of its molecular structure as a dispersant. Even with a small amount added to ferromagnetic fine particles, the strong repulsion of the charge, solvation to water, and strong steric protection each exert a high anti-aggregation effect, and it can be used in water for a long time. The object is to solve the above-mentioned conventional problems by making it possible to stably disperse the ferromagnetic fine particles.

[0007]

The water-based magnetic fluid composition of the present invention that achieves the above object is dispersed in a water-based magnetic fluid composition containing water as a dispersion medium and ferromagnetic fine particles as a dispersoid. A water-soluble polymer is used as an agent.

[0008]

The water-soluble polymer as a dispersant has a large number of anionic hydrophilic groups in its huge molecular structure.
FIG. 1 schematically shows a state in which a water-soluble polymer molecule 10 has a large number of anionic hydrophilic groups 11 and is attached to the particle surface of ferromagnetic fine particles 1. Because of having such a large number of anionic hydrophilic groups 11, the electrostatic repulsion action is large and the solvation action with water as a dispersion medium is large. Moreover, since the chain length is very long, it has a large steric hindrance action. Based on these three actions, aggregation between particles of the water-based magnetic fluid composition can be effectively suppressed, and the ferromagnetic fine particles can be stably dispersed in water for a long period of time.

The water-based magnetic fluid composition of the present invention will be described in detail below. Water-soluble polymers are macromolecules that are readily soluble in water, including natural and synthetic macromolecules. Natural polymers include proteins and starches that are polysaccharides, and synthetic polymers include polyvinyl alcohol, polyethylene oxide, polyacrylamide, polyvinylpyrrolidone,
Examples include polyacrylic acid and sodium polyacrylate. All of these have a structure that easily forms a hydrogen bond with water (eg, peptide bond, ethylene oxide) or a hydrophilic group (eg, —COOH, —COON) in the main chain or side chain.
having _{a, -CONH 2, -SO 3 H} , a -SO ₃ Na, etc.). As the water-soluble polymer of the present invention, those having a molecular structure close to that of sodium polyacrylate are particularly suitable for stably dispersing the ferromagnetic fine particles in water.
That is, a type having a large number of ionizing groups (salt-type hydrophilic groups capable of dissociating counterions in water) in a very long main chain (may have a side chain partially) is preferable. is there. As the main chain, those having relatively high elasticity such as polyisoprene, polybutene, polyisobutylene and polybutadiene are preferable.

The water-soluble polymer has an average molecular weight of 100.
0 to 100,000 is desirable, preferably 10,000
It is a degree. As the hydrophilic group, a carboxyl group,
Metal salts of sulfonic acid groups and phosphoric acid ester groups, particularly alkali metal salts, are preferred. Each hydrophilic group randomly exists in the same chain length, and the type thereof may be single or two or more types. The number of hydrophilic groups is about 10 to 1000, preferably about 100, in one molecule of the dispersant.

Specific examples of the water-soluble polymer used in the present invention include sodium polyisoprenesulfonate and sodium polyisoprenecarboxylate. Next, the ferromagnetic fine particles of the present invention will be described. As the ferromagnetic fine particles, those obtained as a colloidal aqueous suspension (slurry) by a well-known wet method may be used. Here, the wet method means that ferrous ions and ferric ions are 1: 2.
A magnetite colloid is obtained by adding an alkali to an acidic solution containing the above to adjust the pH to about 9 or more and aging at an appropriate temperature. Further, it may be one obtained by a so-called wet pulverization method in which magnetite powder is pulverized by a ball mill in water or an organic solvent. In addition,
It may be obtained by a dry method.

In addition to magnetite, use is made of ferromagnetic metal oxide fine particles such as manganese ferrite, nickel ferrite, cobalt ferrite, composite ferrite of these and zinc, barium ferrite, or ferromagnetic metal fine particles such as iron or cobalt. You can also The content of the ferromagnetic fine particles is, of course, in the range of 1 to 20% by volume ratio which is generally used in the past, and is further increased by producing via an intermediate medium using water as a solvent. It is also possible to adjust the concentration.

As a method for producing the water-based magnetic fluid composition of the present invention, a wet grinding method using water as a solvent can be used, and as a grinding means, a ball mill, a circulating ultrasonic homogenizer, a nanomizer or the like is efficient. . After crushing, if necessary, particles having a large particle size or particles having low dispersion stability can be removed by centrifugation. It is also possible to adjust to an appropriate concentration by concentration or the like.

Next, examples of the present invention will be described.

[0015]

Example 1 First, 6N NaO was added to 1 l of an aqueous solution containing ferric sulfate and ferric sulfate in an amount of 0.3 mol each.
After adding H _aq until pH becomes 11 or more, add 6 parts of the solution.
The mixture was aged at 0 ° C. for 30 minutes to obtain a magnetite colloid slurry solution. Then, the electrolyte is removed from the slurry by washing with water at room temperature. The above is the process of producing magnetite colloid by the wet method. The magnetite colloidal solution thus obtained was centrifuged to recover only magnetite, which was dried under reduced pressure at 80 ° C. for 3 hours.

15.0 g of the dried magnetite particles
As a dispersant, a water-soluble polymer Dynaflow P103
[Nippon Synthetic Rubber Co., Ltd., average molecular weight 10,000, hydrophilic group-
_{COONa: -SO 3 Na = 4:} 1, solid content 40.8 percent, other water] 5.5 g and water 26.3g were added thereto to carry out a 4-hour milling and dispersing operation by using a ball mill. Thus, a dispersion liquid was obtained in which the magnetite fine particles whose surface was coated with the water-soluble polymer were stably dispersed in water.

This dispersion was centrifuged to give 800
The particles were treated for 30 minutes under a centrifugal force of 0 G, and among the particles dispersed in magnetite, particles having a relatively large particle size and poor dispersibility were sedimented and removed. The supernatant obtained by this centrifugation operation was an extremely stable magnetic fluid.

[0018]

[Example 2] A slurry of magnetite colloid was produced by a wet method in the same manner as in Example 1 above, and washed with water at room temperature to remove the electrolyte in this slur. In 500 ml of a slurry containing 50 g of the magnetite fine particles, a water-soluble polymer Dynaflow K106 [manufactured by Japan Synthetic Rubber Co., Ltd., sodium polyisoprenesulfonate as a main component, average molecular weight 40,000, hydrophilic group-SO ₃ Na, Solid content 40
%, Water for others, 20 g was added, and the mixture was transferred to a circulating ultrasonic homogenizer and pulverized and dispersed for 2 hours. Thus, a dispersion liquid was obtained in which the magnetite fine particles whose surface was coated with the water-soluble polymer were stably dispersed in water.

The dispersion is centrifuged at 8000
It was treated for 30 minutes under the centrifugal force of G, and among the magnetite dispersed particles, particles having a relatively large particle diameter and poor dispersibility were sedimented and removed. The supernatant obtained by this centrifugation operation was an extremely stable magnetic fluid.

[0020]

According to the present invention, as a dispersant for stably dispersing ferromagnetic fine particles in a water-based dispersion medium, it is inexpensive, has a large electrostatic repulsion action and a solvation action with water, and has a long chain length. Since it uses a water-soluble polymer that has a long and large steric hindrance effect, high dispersion stability of ferromagnetic fine particles can be secured in water for a long period of time, and the addition amount of a dispersant is small, which is inexpensive and highly profitable. The effect that a water-based magnetic fluid composition can be provided is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a water-based magnetic fluid composition of the present invention.

FIG. 2 is a conceptual diagram of a conventional water-based magnetic fluid composition.

FIG. 3 is a conceptual diagram of another conventional water-based magnetic fluid composition.

[Explanation of symbols]

 1 Ferromagnetic Fine Particles 10 Water-Soluble Polymer

Claims (1)

[Claims] 1. A water-based magnetic fluid composition comprising water as a dispersion medium and ferromagnetic fine particles as a dispersoid, wherein a water-soluble polymer is used as a dispersant.