JPH0752687B2 - Heat-meltable magnetic body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is to disperse ferromagnetic fine particles in a heat-meltable manner so that the ferromagnetic particles aggregate with each other in a normal gravitational field and magnetic field during melting. The present invention relates to a heat-fusible magnetic material that maintains dispersion without any action and behaves as a magnetic fluid, and a method for producing the same.

(Prior Art) A magnetic fluid is a colloidal system in which ferromagnetic fine particles are dispersed and stabilized in a liquid, and behaves as if the liquid had ferromagnetism.

Regarding magnetic fluids, Japanese Patent Publication No. 53-17118 “Method for producing magnetic fluid using oil as dispersion medium”, Japanese Patent Publication No. 53-13436 “Method for producing magnetic fluid using ester and ether as solvent”, Japanese Patent Publication No. 53-13437 "Method for producing magnetic fluid using fluorocarbon as solvent" and JP-B 54-40069 "Method for producing magnetic fluid using water as dispersion medium", etc. By
A method for producing a magnetic fluid by stably dispersing this in a liquid such as oils, esters and ethers, fluorocarbons and water has been disclosed.

(Problems to be solved by the invention) However, in such a magnetic fluid, when a magnetic field is applied to the magnetic fluid, dispersed particles are oriented to form clusters, and needle-like protrusions called spikes are formed on the surface. It is well known that such phenomena occur, but all of these phenomena disappear when the magnetic field is shut off, and there is no retention.

However, if it is a magnetic fluid that melts and becomes a solid at room temperature, it can be retained as a storage medium by retaining clusters and spikes generated by applying a magnetic field at high temperature even after the magnetic field is blocked after cooling.

Further, magnetic fluids are also used as inks for inkjet printers at times, but if magnetic fluids that become solid at melting and become solid at room temperature are used as inks and printing is performed at the time of melting, it is The printed matter will have high physical and chemical durability and high print density.

Therefore, it is an object of the present invention to provide a novel magnetic fluid that is solid at room temperature, fluidizes by heating, and behaves as a magnetic fluid, thereby further expanding the applications of the magnetic fluid.

(Means for Solving Problems) In order to solve the above problems, in the present invention, a wax or a thermoplastic polymer having a melting temperature of room temperature or higher is used as a dispersion medium, and ferromagnetic fine particles are dispersed. It is to provide a magnetic body and a manufacturing method thereof.

As the ferromagnetic fine particles used in the present invention, it is possible to use ferrite fine particles synthesized by a wet method or finely pulverized ferrite synthesized by a dry method.

Wet synthesis involves adding caustic alkali or ammonia to an aqueous solution containing at least one of Fe ³⁺ and Fe ²⁺ , Mn ²⁺ , Zn ²⁺ , Ni ²⁺ , Co ²⁺ , Mg ²⁺ or Cu ^2+. However, PH of 9 or more is desirable
A value of 11 or more is used to crystallize ferrite.

Dry synthesis is iron, manganese, zinc, nickel, cobalt,
It is carried out by mixing magnesium or an equivalent oxide or carbonate in a predetermined ratio and heat-treating at about 1000 to 1500 ° C.

In the wet method, ferrite particles having a desired particle size can be obtained by changing the crystallization conditions, but in the dry method, pulverization for a long time is necessary.

Regarding the particle size of the magnetic fine particles, the particle size of the magnetic fluid fine particles of the conventional magnetic fluid is said to be smaller than about 100Å, but in the magnetic fluid of the present invention, (a) the surface activity of the magnetic particles is coated. The agent layer is thick, the repulsive energy between particles is large, and (b) when the dispersion medium is in a molten state, the dispersed particles are violently in thermal motion due to high temperature.
(C) Since the ferromagnetic material decreases its magnetization as the temperature rises,
Since the magnetic fluid of the present invention has characteristics such as reduced magnetization when melted, it is much less likely to undergo magnetic aggregation than conventional magnetic fluids, and magnetic fluids can be obtained in a wide particle size range of 50 to 500Å.

It should be noted that at 50 Å or less, the magnetization becomes extremely small, which is not practical. Also, if it is 500 Å or more, the dispersion becomes difficult.

Further, in the present invention, the dispersion medium is room temperature or higher, for example, 30 ° C.
Waxes or thermoplastic polymers having the above melting temperatures can be used.

Among these waxes and thermoplastic polymers, paraffin wax, microcrystalline wax, polyethylene wax, Fischer-Tropsch wax, carnauba wax, rice wax, ozokerite, ceresin, beeswax, lanolin, polyethylene, polypropylene, polystyrene, ethylene-vinyl acetate. Copolymers and the like are suitable, and in order to adjust the melting point, hardness, melt viscosity, adhesion to other substances, etc., two or more of these may be used in combination.

Further, the surfactant used as a dispersant in the present invention is, particularly according to the study by the present inventors, one or more --COOX groups or --SO ₃ per molecule for a hydrocarbon group having 21 or more carbon atoms. It is preferable to introduce an X group (X is H, NH ₃ , or an alkali metal) from the viewpoint of stably dispersing a magnetic substance in a wax or a thermoplastic polymer, and a surfactant corresponding to this is behenic acid ( Or a salt thereof, behenine sulfonic acid (or a salt thereof) α-olefin-derived carboxylic acid, and the like.

However, the molecular weight of the surfactant is closely related to the molecular weight of the dispersion medium, and it is preferable that the molecular weight of the dispersion medium is close to that of the dispersion medium. Is difficult to obtain. On the other hand, various waxes have a molecular weight similar to that of the above-mentioned dispersion medium and are easily available.

Therefore, those waxes which have been previously saponified with a caustic alkali solution to impart hydrophilicity may be used as a dispersant, and effective waxes used for this are candelilla wax, carnauba wax, rice wax, montan. Wax, oxidized paraffin wax, oxidized microcrystalline wax, oxidized petroleum,
Examples thereof include oxidized polyethylene wax, acid-modified polyethylene wax, and α-olefin-based synthetic wax.

The magnetic magnetic material according to the present invention is prepared by adsorbing a surfactant on ferromagnetic fine particles having a particle size of 50 to 500Å suspended in water and dispersing it in wax or a thermoplastic polymer heated and melted after dehydration, or Particle size 50-500Å to wax or thermoplastic polymer containing heat-melted surfactant
It can be manufactured by adding and dispersing the ferromagnetic fine particles.

(Advantages of the Invention) In a conventional magnetic fluid, position change, shape change, or orientation of dispersed particles occur due to application of a magnetic field, but these changes disappear and are preserved when the magnetic field is blocked. Can not.

However, since the waxes or the thermoplastic polymers which are solid at room temperature are used as the dispersion medium in the magnetic material according to the present invention, the ferromagnetic particles contained in the magnetic particles are applied by applying a magnetic field when the dispersion medium is melted. Position change, shape change, orientation change, etc., but these changes do not disappear even if the magnetic field is interrupted by cooling and solidifying the dispersion medium while the magnetic field is still applied, It has the characteristic that it cannot be retained by conventional magnetic fluids.

Further, in the present invention, the ferromagnetic fine particles are coated with a special dispersant so that the particles can be extremely stably dispersed in the wax or thermoplastic polymer which has been melted by heating even in a wide range of particle diameters of 50 to 500Å.

(Example) Hereinafter, the Example of this invention is shown.

Example 1 500 ml ferrous sulfate 1 mol aqueous solution and ferric sulfate 1 mol aqueous solution 500
6 ml of sodium hydroxide aqueous solution was added to the mixture to make PN11.5 while stirring. This liquid was kept at 70 ° C. for 30 minutes to age the magnetite. The specific surface area of this magnetite is BE
When measured by the T method, the particle size is estimated to be about 100Å at 120 m ² / g. On the other hand, behenic acid (50 g) was added to warm water (950 g) and adjusted to pH10 with 6N sodium hydroxide aqueous solution, mixed with the magnetite suspension obtained as described above, and mixed at 60 ° C at 60 ° C.
The adsorption reaction was carried out for a minute. After the reaction was completed, 1N hydrochloric acid was added dropwise to adjust the pH to 5 to 6 to agglomerate the suspension, which was thoroughly washed with water and then suction filtered to obtain a water-containing cake. The water-containing cake was washed with acetone, suction-filtered again, and then air-dried at room temperature to obtain a dry powder. 25 g of the dry powder thus obtained was added to 20 g of melted paraffin wax (SP-0110, manufactured by Nippon Seiro Co., Ltd., melting point 44 ° C.) and stirred while heating to obtain a uniform dispersion liquid. Place the beaker containing this dispersion on the barium ferrite magnet,
When left in an air bath at ℃ for one day, a few aggregates were found at the bottom of the beaker. When the aggregates were removed and then allowed to stand again under the same conditions, no new aggregates were found to be formed, and it was confirmed that they were completely converted to magnetic fluid.

The dispersion was cooled to room temperature and solidified, and the magnetic measurement was performed. The result was as shown in FIG. In addition, the properties did not change at all even when the cycle of melting-cooling and solidification was repeated.

Example 2 A dry powder was obtained in the same manner as in Example 1 except that 55 g of sodium behenine sulfonate was used instead of behenic acid. 25 g of the obtained dry powder was added to melted paraffin wax (SP-3040, manufactured by Nippon Seiro Co., Ltd., melting point 63 ° C.) and stirred while heating to obtain a uniform dispersion liquid. When the same operation as in Example 1 was performed on this dispersion, a heat-meltable magnetic fluid having a magnetization of 25 emu / g (magnetic field 8 KO _e ) at room temperature was obtained.

Example 3 Carnauba wax (manufactured by Nisshin Kasei, Carnauba No. 1) 140 g
Was added to 100 g of hot water, and 6N sodium hydroxide was added dropwise to add PH.
The emulsion was adjusted to 9.5. This liquid was mixed with a magnetite suspension prepared in the same manner as in Example 1, and the mixture was mixed at 80 ° C.
The adsorption reaction was carried out for 60 minutes. After completion of the reaction, a dry powder was obtained in the same manner as in Example 1. 25g of this powder melted microcrystalline wax (Ni-sei Seiwa Co., Ltd., Hi-Mic1
070, melting point 80 ° C) and paraffin wax (the same, paraffin wax 155, melting point 69 ° C) added to 20 g of an equal mixture,
A uniform dispersion was obtained by stirring with heating.
When the same operation as in Example 1 was performed on this dispersion, a heat-meltable magnetic fluid having a magnetization of 20 emu / g (magnetic field 8 KO _e ) at room temperature was obtained.

Example 4 Acid-modified polyethylene wax (Mitsui Petrochemical Industry Co.,
Mitsui High Wax 1105A, molecular weight 1500) 75g and petrolatum oxide (Nippon Seiwa Co., Ltd., OX-0450) 75g were added to hot water 1000g, and 6N sodium hydroxide was added dropwise to adjust the pH to 9.5 to obtain an emulsion. It was This liquid was mixed with a magnetite suspension prepared in the same manner as in Example 1, and an adsorption reaction was carried out at 80 ° C. for 60 minutes. After completion of the reaction, a dry powder was obtained in the same manner as in Example 1. 25g of this dry powder melted microcrystalline wax (Microwax, Microwax
190Y, melting point 83 ° C) and polyethylene wax (Mitsui Petrochemical Co., Ltd., Mitsui High Wax 110P, melting point 109 ° C) were added to 30 g of an equal mixture and stirred while heating to obtain a uniform dispersion liquid. A beaker containing this dispersion was placed on a barium ferrite magnet and allowed to stand still for one day in an air bath at 120 ° C. A few agglomerates were found at the bottom of the beaker. When this agglomerate was removed and allowed to stand again under the same conditions, no new agglomerate was observed and it was confirmed that the ferrofluid was completely formed.

Example 5 Manganese sulfate, zinc sulfate, and ferric sulfate 1 mol each of 1 mol aqueous solution were sampled in 250 ml, 250 ml, and 500 ml, respectively, and mixed into one liquid. A 6N sodium hydroxide aqueous solution was added to this while stirring to make PH11, and then aged at 90 ° C for 20 minutes to obtain a manganese zinc ferrite suspension. Manganese thus obtained
When the specific surface area of zinc ferrite particles was measured by the BET method, the particle size was estimated to be about 200Å at 60 m ² / g. On the other hand, Montan Wax (Hoechst Wax BJ) 150g, hot water 1000g
In addition, 6N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 9.5 to obtain an emulsion, and this was mixed with the manganese-zinc ferrite suspension obtained as described above at 60 ° C at 60 ° C. The adsorption reaction was carried out for a minute. After completion of the reaction, a mixture of microcrystalline wax (Hi-Mic 2095, melting point 96 ° C., manufactured by Nippon Seiro Co., Ltd.) obtained by melting 25 g of dry powder obtained in the same manner as in Example 1 and montan wax (Hoechst wax E) (mixing ratio) 4: 1) was added to 30 g and stirred while heating to obtain a uniform dispersion liquid. Example 4 for this dispersion
When the same operation as above was performed, the magnetization at room temperature was 20 emu / g.
A hot-melt magnetic fluid with a magnetic field of 8 KO _e was obtained.

The change in magnetization of the obtained magnetic material with respect to temperature in a magnetic field of 8 KO _e was as shown in FIG.

Example 6 50 ml, 50 ml and 100 ml of 1 mol solutions of nickel sulfate, zinc sulfate and ferric sulfate were respectively taken and mixed into one liquid.
A 6N sodium hydroxide aqueous solution was added to this to obtain PH11, which was then transferred to an autoclave and aged at 120 ° C for 5 hours to obtain a nickel-zinc ferrite suspension. The specific surface area of the nickel-zinc ferrite particles thus obtained is
When measured by the BET method, the particle size is estimated to be about 300Å at 40 m ² / g. On the other hand, 15 g of α-olefin derived wax (PA30L manufactured by Mitsubishi Kasei Co., Ltd.) was added to 200 g of hot water, and 6N aqueous sodium hydroxide solution was added dropwise to adjust the pH to 9.5 to obtain an emulsion, which was taken out from the autoclave. It was mixed with the ferrite suspension prepared above and adsorbed at 80 ° C. for 60 minutes. After completion of the reaction, 25 g of dry powder obtained in the same manner as in Example 1 was melted to melt polyethylene wax (Mitsui High Wax 220P, melting point 1
10 ° C) and ethylene-vinyl acetate copolymer (Evaflex 450, manufactured by Mitsui Polychemical Co., Ltd.) (mixing ratio 9: 1)
When added to 30 g and stirred with heating, a uniform dispersion was obtained. When this dispersion was operated in the same manner as in Example 4, it was confirmed to be a magnetic fluid.

Example 7 10 g and 30.4 g of manganese dioxide (reagent special grade) and ferric oxide (reagent special grade) finely pulverized to 50 μm or less were uniformly mixed, and heat treated at 1200 ° C. in a nitrogen atmosphere to obtain manganese ferrite. This was put in a centrifugal ball mill together with kerosene and pulverized for 120 hours. On the other hand, 25 g of polyethylene wax (Hoechst wax PP230) and 25 g of Fischer-Tropsch wax (Crystal wax 220, Mobil Oil Co., Ltd.) were melted by adding 5 g of α-olefin-derived monocarboxylic acid type wax (BMA30, Mitsubishi Kasei Co., Ltd.). The manganese ferrite powder obtained by crushing was added together with kerosene, and the kerosene was evaporated with heating and stirring, whereby a uniform dispersion liquid was obtained.
A beaker containing this solution was placed on a barium ferrite magnet and allowed to stand in an air bath at 160 ° C. for 6 hours, whereupon agglomerates were observed at the bottom of the beaker. When this aggregate was removed and the mixture was allowed to stand again under the same conditions, no new aggregate was generated, and it was confirmed that it was a magnetic fluid. The average particle size of the dispersed particles was 500Å according to an electron microscope observation.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a magnetic field and a dispersion liquid magnetization when a magnetic field is applied in a state where the dispersion liquid obtained in Example 1 is cooled and solidified to room temperature, and FIG. 2 is obtained in Example 5. 8K of magnetic material
FIG. 6 is a diagram showing a relationship between temperature and a change in magnetization in a magnetic field of O _e .

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Claims (5)

[Claims] 1. A wax or thermoplastic polymer having a melting temperature of room temperature or higher is used as a dispersion medium, and ferromagnetic fine particles have one or more --COOX groups per molecule for hydrocarbon groups having 21 or more carbon atoms, or -SO ₃ X heat (X is H, NH ₃ , or an alkali metal) as a dispersoid that is adsorbed and coated with a surfactant that has been introduced or a wax that has been rendered hydrophilic by saponification with a caustic solution. Meltable magnetic substance. 2. The heat-fusible magnetic material according to claim 1, wherein the ferromagnetic fine particles have a particle diameter of 50 to 500Å. 3. The heat fusible magnetic material according to claim 1, wherein the ferromagnetic fine particles are fine particles of a ferromagnetic oxide. 4. Ferromagnetic fine particles having a particle size of 50 to 500Å suspended in water, 1 per molecule of a hydrocarbon group having 21 or more carbon atoms.
Or a plurality of —COOX groups or —SO ₃ X groups (X is H, NH ₃ ,
Or a alkali metal) -introduced surfactant, or waxes that have been rendered hydrophilic by saponification with a caustic alkali solution are adsorbed and dispersed in waxes or thermoplastic polymers that are heated and melted after dehydration. Manufacturing method of meltable magnetic material. 5. A hydrocarbon group having 21 or more carbon atoms has 1 per molecule.
Or a plurality of —COOX groups or —SO ₃ X groups (X is H, NH ₃ ,
(Or an alkali metal) introduced surfactant, or a dispersant consisting of waxes saponified with a caustic alkali solution to impart hydrophilicity is heated and melted, and mixed with waxes or a thermoplastic polymer as a dispersion medium, and Particle size
A method for producing a heat-meltable magnetic material, which comprises adding 50 to 500 Å ferromagnetic fine particles and dispersing them.