JPH0529662B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a liquid-based or powder-based magnetic material for magnetic paint. Here, the liquid system refers to a dispersion system in which cobalt-containing magnetic iron oxide is dispersed in an organic solvent, and the powder system refers to the cobalt-containing magnetic iron oxide powder itself. Conventionally, cobalt-containing magnetic iron oxide, which is a magnetic material for magnetic paints, has been obtained by the following manufacturing methods. When obtaining acicular hydrated iron oxide, cobalt ions are allowed to coexist, and the manufacturing conditions of hydrated iron oxide are changed, for example,
A method of co-precipitating cobalt ions into hydrated iron oxide by adjusting the temperature and pH, and then firing this to form magnetic iron oxide. Acicular iron oxide (hydrous iron oxide; α-Fe ₂ O ₃ :
A method in which xFe ₂ O ₃ (0<x<1) is mixed or coated with a cobalt compound and then fired. A method of tightly coating a magnetic iron oxide surface with a cobalt compound. However, in order to disperse the magnetic powder obtained by these conventional manufacturing methods into a paint and make it into a magnetic paint, in addition to steps such as filtration, washing, drying, and pulverization, further dispersion into the paint and surface treatment are required. In the process of forming an adsorption layer of surfactant or polymer on the powder surface to improve the wetting properties as a modification, or in the case of premixing, it is difficult to loosen it to the state of primary particles because it is over-dried. There are many drawbacks, such as the need for a powerful dispersion machine and the many different steps required to create a magnetic paint, so great care was required. Many of these drawbacks were thought to be due to the use of water as a solvent. Therefore, in recent years, ferromagnetic iron oxide powder is dispersed in a solution consisting of an organic solvent and a metal compound soluble in the organic solvent, and the metal is introduced into the ferromagnetic iron oxide particles by heat treatment. A new law was developed (Special Publication No. 56-31729). However, the organic solvents used in this manufacturing method are alcohol, fatty acids, semi-drying oils, fatty acid esters, oxycarboxylic acids, dimethylformamide, or dimethyl oxide, which are completely unsuitable as solvents for magnetic paint binders. These are all organic solvents. Therefore, the reaction system obtained by this method, in which metal is introduced into ferromagnetic iron oxide particles, cannot be directly used as a magnetic paint, and the organic solvent of the reaction system must be distilled off. The powder was made into magnetic powder and then used in magnetic paints. Moreover, the magnetic powder needs to be washed and dried, and when dispersed in a solvent, it has poor wettability with the solvent of the binder for magnetic paint, and its dispersibility in the paint is poor. It also has the disadvantage of requiring many steps such as washing, drying, and re-grinding. As a result of various studies in view of the above-mentioned circumstances, the inventors of the present invention have developed a coating material that is a final product by carrying out a reaction in which cobalt is introduced into particles of ferromagnetic iron oxide in the solvent of a binder for magnetic coating material. The present invention was completed by discovering that it is possible to improve the dispersion in the liquid and simplify the process. The gist of the present invention is to dissolve a cobalt compound in a mixed organic solvent of one or more of aromatics, ketones, saturated hydrocarbons, ethers, or halogenated hydrocarbons, and then The acicular magnetic iron oxide powder is dispersed in the liquid, and then the dispersion system is heated to react, and then cooled to room temperature to form a liquid dispersion system (first invention), or the organic solvent is distilled off. This is a method for producing powdered magnetic material for magnetic paint (second invention). Hereinafter, the present invention will be specifically explained in accordance with the order of the steps. First, a cobalt compound is dissolved in an organic solvent. Organic solvents are used as binder solvents for magnetic paints, and examples include toluene, xylene, and ethylbenzene for aromatics, and methyl ethyl ketone, methyl isobutyl ketone, acetone, cyclohexanone, and saturated ketones. Examples of hydrocarbons include cyclohexane and methylcyclohexane, examples of ethers include dibutyl ether and amyl ether, and examples of halogenated hydrocarbons include chloride-2-ethylhexyldichloropentane, and one or more of these are selected. It can be used alone or as a mixed organic solvent. Incidentally, examples of the binder for magnetic paint include vinyl chloride/vinyl acetate copolymer, polyurethane resin nitrocellulose, and the like. Cobalt compounds include the above-mentioned inorganic salts and organic salts that are soluble in organic solvents, as well as chelate compounds, complex salts,
Ionic aggregates are also included, and they do not necessarily need to be soluble at room temperature and normal pressure, as long as they are soluble even if slightly soluble under heating or pressure during the reaction. For example, cobalt naphthenate, cobalt 2-ethylhexanoate, or cobalt acetate is used as the organic salt, and cobalt chloride, cobalt sulfate, cobalt carbonate, etc. are used as the inorganic salt. Next, in the present invention, acicular magnetic iron oxide is dispersed in the above-mentioned dissolved system of the cobalt compound, and then the dispersion system is heat-treated. Through this heat treatment, cobalt reacts with the acicular magnetic iron oxide and is introduced. This heat treatment may be performed simply by heating the dispersion system to an appropriate temperature. The above heating may be carried out under normal pressure, but depending on the type of organic solvent used, the reaction may be carried out by heating and pressurizing in an autoclave or the like. The relationship between the amount of cobalt added and the coercive force in this reaction, and the relationship between the reaction temperature and the coercive force are as follows. The table below shows the results of a reaction in an autoclave using toluene as an organic solvent and cobalt naphthenate as a cobalt compound, while keeping the reaction time constant (6 hours) and varying the amount of cobalt naphthenate added and the reaction temperature. .

[Table] *2: After the completion of the reaction, the organic solvent was distilled off, and the dried product powder was measured.
Test Nos. 1 to 3 were conducted by changing the amount of cobalt naphthenate added from 1.5 to 3.5 at a constant reaction temperature (220°C), and at this time, the cobalt content of the product and the coercive force of the product The relationship is shown in Figure 1. In addition, in Test Nos. 1, 4, and 5, the reaction temperature was set at 200 to
The temperature was changed to 240°C, and the relationship between the reaction temperature and the coercive force of the product is shown in Figure 2. The following can be understood from FIGS. 1 and 2. That is, in the production method according to the present invention, the coercive force of the product can be increased by increasing the amount of cobalt compound added, as seen in FIG. 1, and the reaction The coercivity of the product can be increased by increasing the temperature. As described above, in this reaction system, the coercive force of the product can be controlled by controlling the amount of cobalt compound added and the treatment temperature. These control conditions vary depending on the type of organic solvent used, and it is advisable to set the conditions by conducting a preliminary test. This reaction can be carried out at normal pressure if the organic solvent used has a high boiling point, but even if the organic solvent has a low boiling point, a pressure vessel such as an autoclave is used and the atmosphere is changed to an oxidizing gas, reducing gas, inert gas, etc. I will do it as. Preferably it is nitrogen gas. Further, in the present invention, the dispersion that has been subjected to the heat treatment to complete the reaction is cooled to room temperature to obtain a liquid dispersion magnetic material for magnetic paint, or the organic solvent of the dispersion is distilled off by an appropriate means. A magnetic material for powder magnetic paint is obtained. The above liquid dispersion type magnetic material can also be used to adjust the amount of solvent by distilling off a part of the organic solvent, and when treated under heat and pressure using an autoclave, the pressurized atmosphere in the autoclave can be adjusted. It can be easily adjusted by partially blowing. Further, the above-mentioned powder magnetic material, which has been treated under heat and pressure using an autoclave, can be easily made into a dry powder by blowing out the entire amount of the organic solvent after the reaction is completed. In the present invention, a magnetic material is obtained as described above, but a magnetic paint can be obtained using the magnetic material as follows. That is, in the case of magnetic materials in a liquid dispersion system, it is possible to obtain a magnetic paint extremely easily by adding a binder or a dispersant directly to the dispersion system, and adding an organic solvent to adjust the total amount. In the case of a powder magnetic material, the powder magnetic material is premixed with a binder, an organic solvent, and a dispersant according to a standard method, and then an organic solvent and the like are added and dispersed to obtain a magnetic paint. Since the present invention is configured as described above, the following features are obtained. Since the binder solvent for magnetic paint is used as a reaction solvent, there is no contamination of impurities such as salt into the product, and since no water is used, there is no moisture as a contaminant that degrades wetting properties. There are no. According to the present invention, since the binder solvent is used as the reaction solvent, the dispersibility is improved. In particular, for liquid dispersion type magnetic materials, it is possible to directly obtain magnetic paint by adding binders, dispersants, etc. to the dispersion system, which greatly shortens the conventional manufacturing process. This eliminates the need for large amounts of water and time required to wash away the alkali in the method. Furthermore, since there is no need to pass the product through, there is extremely little loss of the product. Next, examples of the present invention will be described. Example 1 Cobalt naphthenate was adjusted to a Co/γ-Fe ₂ O ₃ weight percentage of 2.0 (wt, %), added to 200 (ml) of toluene as a solvent, and then γ-Fe 2 O 3 was added to this solution.
Fe ₂ O ₃ (Hc: 410 (Oe) σs: 72.0 (emu/g) Axial length
Add 0.4 (μ), axial ratio (8), 50 (g), and further add toluene to make the total volume 4206 (ml). This solution was dispersed using an ultrasonic homogenizer, and while stirring in an autoclave, the reaction temperature
The reaction was carried out at 220°C for 6 hours. After the reaction was completed, about 350 (ml) of the solvent was blown out, the mixture was cooled to normal pressure, and the product was taken out in a concentrated and dispersed state in toluene to obtain a liquid dispersion magnetic material. When a part of the product was dried and its magnetic properties were measured, the following effects were obtained. Coercive force 650 (Oe), saturation magnetization 74.4 (emu/g), squareness ratio 0.52, Fe ²⁺ /Feh ³⁺ 0.07 Co/γ−Fe ₂ O ₃ 2.0 (wt, %) This liquid dispersion magnetic material The magnetic paint was obtained as follows. First, toluene was added to adjust the weight ratio of toluene/magnetic powder in the magnetic material to 50 (g)/50 (g). Thereafter, a binder and the like were directly added to the above-mentioned adjusted magnetic material according to a conventional method so as to have the composition shown below. Adjusted liquid dispersion magnetic material 100g Nyl-vinyl acetate copolymer (polymerization ratio 91:6)
8.8g Polyurethane resin 3.7g Lecithin 1.0g Methyl isobutyl ketone 50g When this material was coated on a polyester resin film to produce a magnetic tape, a coercive force (680 (Oe)) was obtained. Example 2 2-Ethylhexane Acid cobalt is Co/γ-
Weight percentage of Fe ₂ O ₃ (wt,%) toluene 200
(ml) and further γ-Fe ₂ O ₃ (Hc: 410 (Oe)
50 g of σs 72.0 (emu/g), axial length 0.4 μ axial ratio 8) was added to make the total volume 420 (ml), and the reaction was carried out at a reaction temperature of 220° C. for 6 hours with stirring using an autoclave. At this time, the pressure rose to 8 (Kg/cm ² ). The magnetic properties of the obtained magnetic powder are coercive force 520 (Oe) and saturation magnetization 72.4.
(emu/g), and the squareness ratio was 0.49. Furthermore, when analyzed, Fe ²⁺ /Fe ³⁺ is 0.04 Co/γ
-Fe ₂ O ₃ was 1.7 (wt%). Chlorination Example 3 Cobalt chloride (CoCl ₂ 6H ₂ O) was converted into Co/γ-
Add 4.0 (wt%) in weight percentage _{of Fe2O3} to 200ml of methyl ethyl ketone (MEK) and further add σ-
Fe ₂ O ₃ (Hc: 410 (Oe) σs72.0 (emu/g), axial length 0.4
(μ), axial ratio 8) was added to make the total volume 420 (ml),
While stirring using an autoclave, the reaction temperature was 200℃.
The reaction was carried out at ℃ for 1.5 hours. At this time, the pressure is 20 (Kg/
^cm2 ). The magnetic properties of the obtained magnetic powder have a coercive force of 970 (Oe)
The saturation magnetization was 78.4 (emu/g) and the squareness ratio was 0.53. Furthermore, when analyzed, Fe ²⁺ /Fe ³⁺ is 0.31 Co/γ
_-Fe2O3 was _3.5 (wt, %). Example 4 Cobalt acetate (Co(CH ₃ COO) ₂・4H ₂ O)
A weight percentage of 4.0 (wt%) of Co/γ-Fe ₂ O ₃ was added to 200 (ml) of methyl isobutyl ketone (MIBK), and further γ-Fe ₂ O ₃ (Hc: 410 (Oe) σs: 72.0
(emu/g) Axial length 0.4 (μ) Axial ratio 8) to 50 (g)
The total volume was adjusted to 420 (ml), and the reaction was carried out for 2 hours at a reaction temperature of 200°C using an autoclave. At this time, the pressure rose to 10 (Kg/cm ² ). The magnetic properties of the obtained magnetic powder are coercive force 1130 (Oe),
The saturation magnetization was 74.8 (emu/g) and the squareness ratio was 0.54. Further analysis shows that Fe ²⁺ /Fe ³⁺ is 0.15,
Co/γ-Fe ₂ O ₃ was 3.5 (wt%). Example 5 Cobalt acetate (Co(CH ₃ COO) ₂・4H ₂ O)
The weight percentage of Co/γ-Fe ₂ O ₃ is 4.0 (wt%) of methyl isobutyl ketone (MIBK) and toluene: 1:
Added to 200 (ml) of the mixed solution of 1 and further added γ-Fe ₂ O ₃
(Hc: 410 (Oe) σs72.0 (emu/g), axial length 0.4 (μ)
Add 50 (g) of axial ratio 8) to make the total volume 420 (ml),
The reaction was carried out using an autoclave at a reaction temperature of 200°C for 5 hours. The pressure at this time rose to 10 (Kg/cm ² ). The magnetic properties of the obtained magnetic powder have a coercive force of 860
(Oe), saturation magnetization 75.3 (emu/g), and squareness ratio 0.53. Further analysis shows that Fe ²⁺ /Fe ³⁺ is 0.10, Co/
γ-Fe ₂ O ₃ was 3.3 (wt, %).

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the cobalt content and the coercive force of the product when the reaction time and reaction temperature are kept constant and the amount of cobalt added is varied in the reaction of the present invention. Figure 2 is a graph showing the relationship between the cobalt content and the coercive force of the product. 2 is a graph showing the relationship between the reaction temperature and the coercive force of the product when the cobalt addition amount and reaction time are kept constant and the reaction temperature is varied in the reaction.

Claims (1)

[Claims] 1. A cobalt compound is dissolved in an organic solvent selected from aromatics, ketones, saturated hydrocarbons, ethers, or halogenated hydrocarbons (or a mixture of two or more thereof). Then, after dispersing acicular magnetic iron oxide powder in the above-mentioned melted system, the dispersion system is heat-treated, and after introducing cobalt, the above-mentioned dispersion system is cooled to room temperature to form a liquid dispersion system. Manufacturing method of magnetic material for magnetic paint. 2 A cobalt compound is dissolved in an organic solvent selected from aromatics, ketones, saturated hydrocarbons, ethers, or halogenated hydrocarbons (or a mixture of two or more), and then the above dissolution system is dissolved. A magnetic material for magnetic paint, characterized in that the dispersion system is heat-treated after dispersing acicular magnetic iron oxide powder in water, cobalt is introduced, and the organic solvent of the dispersion system is distilled off to form a powder. Manufacturing method.