JPH0258321B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention involves adding nickel salt or the like to an aqueous suspension of α-iron oxyhydroxide fine particles, attaching a metal compound to the α-iron oxyhydroxide fine particles, and reducing them to form acicular ferromagnetic particles. The present invention relates to a method for producing metal fine particles. [Prior art] Acicular iron oxide particles have traditionally been used as fine particles for magnetic recording media, but with the development of high-performance audio cassette tapes and compact video tapes, recording density and performance have increased. has become more and more required. For this reason, ferromagnetic metallic iron fine particles having magnetic properties, particularly high coercive force and high magnetic flux density, are attracting attention. Ferromagnetic metal fine particles obtained by heating and reducing powders mainly composed of iron oxide or α-iron oxyhydroxide in a stream of reducing gas such as H ₂ are the most widely known materials that can meet this requirement. There is. In order to meet the demands for higher recording density and higher performance, ferromagnetic metal powders are becoming increasingly finer. However, when it is made into fine particles, sintering of the particles becomes more likely to occur during the heating and sintering and reduction steps during production, and the shape retention of the form particles of the α-iron oxyhydroxide fine particles used as the raw material deteriorates. Further, as the particles become finer, the saturation magnetization, which is the most important factor in terms of magnetic properties, decreases, and the coercive force also exceeds the appropriate range and becomes higher than necessary, making it difficult to erase by the head.
Furthermore, corrosion resistance, which is one of the biggest drawbacks of ferromagnetic metal powder, is further reduced. That is, various problems arise in the dispersibility, saturation magnetization, coercive force, and corrosion resistance of the ferromagnetic metal powder due to the finer particles. These problems have been greatly improved by the method disclosed in Japanese Patent Application No. 61-253989. This application involves depositing a metal compound on the surface of α-iron oxyhydroxide particles in water, then depositing a silicon compound and an aluminum compound in alkaline water, and then heating in a non-reducing gas atmosphere. In the method of producing ferromagnetic metal fine particles by firing and then reducing under heating, the α-iron oxyhydroxide particles are suspended in an organic acid aqueous solution with a pH of 4.0.
Add metal salt to the following and then add ammonia to make a slurry with a pH of 9.0 to 11.0. After aging at 70℃ or higher, add ammonia as necessary to keep the slurry pH at 7 or higher. The patent discloses a method in which a silicon compound and an aluminum compound are added to the slurry, the temperature of the slurry is raised to 70° C. or higher, the α-iron oxyhydroxide particles are separated, dried, heated and calcined, and then reduced. This method provides dispersibility,
Various problems regarding saturation magnetization, coercive force, and corrosion resistance have been resolved, and it has become possible to satisfy excellent characteristics in a well-balanced manner. By the way, magnetic tapes made using ferromagnetic metal powder must not only have excellent magnetic properties and corrosion resistance, but also have excellent running durability. That is, magnetic tapes made using ferromagnetic metal powder generally have poor running durability, and during repeated playback or still playback, there is a strong tendency for the output to decrease due to falling off of the magnetic powder, clogging of the head, etc. Conventionally, measures to improve this decrease in output include improving the binder to strengthen the adhesion between the magnetic coating and the base film to prevent the magnetic coating from peeling off, and using abrasives to remove clogging of the magnetic head. It is being Conventionally, as a measure to remove clogging of the magnetic head, a method has been adopted in which an abrasive such as aluminum oxide powder or chromium oxide powder is added at the stage of turning magnetic powder into paint, and the magnetic head is constantly cleaned. In this case, the abrasive material tends to roughen the surface of the magnetic tape, which may increase noise in electromagnetic characteristics or cause dropouts, which is undesirable. Therefore, in order to constantly clean the magnetic head, it is necessary to impart an appropriate polishing effect to the magnetic powder itself. Many proposals have been made to properly polish the magnetic head and prevent clogging of the magnetic head, but ferromagnetic metal fine particles with excellent magnetic properties, especially high coercive force and high saturation magnetization, have excellent paint dispersibility. A method for producing fine particles that has such properties and at the same time has a suitable polishing effect on magnetic heads has not yet been found. [Problems to be Solved by the Invention] The purpose of the present invention is to provide excellent magnetic properties, particularly high coercive force,
An object of the present invention is to provide a method for producing ferromagnetic metal fine particles having high saturation magnetization, excellent paint dispersibility, and excellent running durability. [Means for Solving the Problems] As a result of extensive research into the production of ferromagnetic metal powders that have even greater paint dispersibility and superior coating strength in magnetic tapes, the present inventors have found that α-
After adding an aqueous solution of nickel salt to a suspension (slurry) of an organic acid aqueous solution of iron oxyhydroxide particles, an aqueous solution of silicic acid or a silicate and an aqueous solution of monobasic aluminum phosphate as an aluminum compound are added, By subsequently adding an aqueous solution of chromium salt, drying α-iron oxyhydroxide separately, and reducing it after heating and firing,
The present invention was accomplished by discovering that ferromagnetic metal fine particles can be obtained that provide a magnetic tape with excellent magnetic properties, extremely excellent dispersibility, and at the same time excellent running durability. That is, in the present invention, an aqueous solution of nickel salt is added to a suspension (slurry) of an organic acid aqueous solution of α-iron oxyhydroxide fine particles, and the pH of the slurry is 4.0 or less, and ammonia is added to adjust the pH of the slurry.
9.0 to 11.0 and aged at 70°C or higher to firmly adhere the nickel compound to the surface of the α-iron oxyhydroxide fine particles, then add ammonia as necessary to keep the pH of the slurry at 7.0 or higher. At the same time, silicic acid or an aqueous solution of a silicate and an aqueous solution of monoaluminum phosphate are added to attach a silicon compound and an aluminum compound to the surface of the α-iron oxyhydroxide particles to which the nickel compound has been attached, and then Add ammonia as needed to adjust the pH of the slurry.
7.0 or higher, add an aqueous solution of chromium salt, attach the chromium compound to the outermost layer of the α-iron oxyhydroxide fine particles to which the nickel compound, silicon compound, and aluminum compound have been attached, and add this slurry to the slurry using an excessive method. This is a method for producing fine ferromagnetic metal particles by drying after separation to obtain dry α-iron oxyhydroxide fine particles, which are then heated and fired and then reduced. To explain this in detail, first, a suspension (slurry) of an organic acid aqueous solution of α-iron oxyhydroxide fine particles
Prepare. For this purpose, an organic acid may be added to an aqueous suspension of α-iron oxyhydroxide fine particles, or α-iron oxyhydroxide fine particles may be added to an organic acid aqueous solution. The pH of the slurry of the organic acid aqueous solution of α-iron oxyhydroxide fine particles is preferably 4.0 or less. Preferably it is 3.5 to 2.0. In this PH region,
Fine particles of α-iron oxyhydroxide that had formed aggregates are uniformly dispersed into single particles. In this state, an aqueous solution of an inorganic salt or an organic acid salt of nickel is added. Thereafter, ammonia is added to adjust the pH of the slurry to 9.0 or more, preferably in the range of 9.5 to 11.0, and nickel hydroxide is precipitated on the surface of the α-iron oxyhydroxide fine particles. Then, the mixture is aged by heating or boiling to firmly adhere the nickel compound to the surface of the α-iron oxyhydroxide fine particles.
At this time, the temperature of the slurry is 70°C or higher, the higher the better.
Preferably the temperature is 90°C or higher. Also, the aging time is 30
It is good for 1 minute to 2 hours, preferably 1 hour to 2 hours. The slurry is then cooled or preferably above 70°C.
Maintain the pH of the slurry at 7.0 or higher by adding ammonia as needed while keeping the temperature at 90°C or higher, and gradually add an aqueous solution of silicic acid or silicate and an aqueous solution of monobasic aluminum phosphate. When added during cooling, the slurry is preferably heated to 70°C or higher, preferably 90°C or higher. It is best to age it for 30 minutes to 2 hours. The slurry is then cooled or preferably above 70°C.
While keeping the temperature above 90°C, add ammonia as needed to maintain the pH of the slurry above 7.0, and gradually add an aqueous solution of chromium salt. If an aqueous solution of chromium salt is added during cooling, the temperature should be 70°C or higher, preferably 90°C.
Heat the slurry above °C. And mature.
Aging time is 30 minutes to 2 hours, preferably 1 hour.
2 hours is good. Next, the slurry is cooled to around room temperature and then filtered. After that, it is dried to obtain dry α-iron oxyhydroxide treated with each metal, which is heated and calcined and then reduced with a reducing gas such as hydrogen. The α-iron oxyhydroxide used as a starting material in the present invention may be either a dry powder or a wet cake of acicular α-iron oxyhydroxide. The organic acid used in the present invention can be any of acetic acid, formic acid, citric acid, oxalic acid, etc., but acetic acid is preferred from the viewpoint of dispersion ability. As the aqueous solution of nickel salt used in the present invention, an aqueous solution of an inorganic salt such as nickel sulfate, nickel nitrate, or nickel chloride, or an aqueous solution of an organic acid salt such as nickel acetate or nickel oxalate can be used. Aqueous solutions are particularly preferred. The amount of the aqueous solution of the nickel salt added is preferably 1 to 30 parts by weight based on nickel atoms per 100 parts by weight of iron atoms of α-iron oxyhydroxide. If the amount of nickel added is less than 1 part by weight, there is no effect, and if it is more than 30 parts by weight, the effect is saturated. In the present invention, ammonia may be added by any method such as addition as aqueous ammonia or blowing in ammonia gas until the pH of the slurry is 9.0 or more.
Just add it so that it becomes 11.0. Instead of ammonia, a substance such as urea that can be thermally decomposed by heating in an aqueous solution state to produce ammonia may be used. This case is also included in the present invention. The aqueous solutions of silicic acid or silicate used in the present invention include aqueous solutions of various silicic acids such as ortho-silicic acid and meta-silicic acid, aqueous silica sol, aqueous silica sol stabilized with ammonia, and aqueous solutions modified with aluminum. Examples include silica sol and aqueous solution of sodium silicate. The amount of silicon added to these aqueous solutions or sols is based on silicon atoms per 100 parts by weight of iron atoms of α-iron oxyhydroxide.
0.5 to 7 parts by weight, preferably 0.7 to 5 parts by weight.
If it is less than 0.5 parts by weight, there is no sintering prevention effect, and if it is more than 7 parts by weight, reduction is suppressed and desired magnetic properties, especially high saturation magnetization, cannot be obtained. The amount of the monoaluminum phosphate aqueous solution used in the present invention is 0.5 to 0.5 to 100 parts by weight of iron atoms of α-iron oxyhydroxide based on aluminum atoms.
7 parts by weight, preferably 0.7 to 5 parts by weight. As the aqueous solution of chromium salt used in the present invention, an aqueous solution of an inorganic salt such as chromium chloride, chromium nitrate, chromium sulfate, or chromium phosphate, or an aqueous solution of an organic acid salt such as chromium formate or chromium acetate can be used. Chromium nitrate and chromium acetate are preferred. The amount of chromium added to these aqueous solutions is 0.3 to 0.3 to 100 parts by weight of iron atoms in α-iron oxyhydroxide based on chromium atoms.
The amount is preferably 10 parts by weight, preferably 0.5 to 7 parts by weight. If it is less than 0.3 parts by weight, it will not be possible to impart a suitable polishing effect to the ferromagnetic metal fine particles, and if it is more than 10 parts by weight, desired magnetic properties, particularly high saturation magnetization, will not be obtained. When adding silicic acid or silicate aqueous solution, monobasic aluminum phosphate aqueous solution, and chromium salt aqueous solution, the pH of the slurry should preferably be 7.0 or higher.
8.0-11.0 is good. This is because if the temperature is outside this range, the deposited metal will easily dissolve. The slurry obtained by adding an aqueous solution of nickel salt, an aqueous solution of silicic acid or a silicate, an aqueous solution of monobasic aluminum phosphate, and an aqueous solution of chromium salt in the above operation is separated by an appropriate method, and then the necessary It is washed with water and then dried to obtain dry α-iron oxyhydroxide. This drying temperature is preferably 100 to 180°C. This dried α-iron oxyhydroxide is first heated and calcined to form a single acicular hematite crystal, and then reduced to form a ferromagnetic metal powder. Heating and firing is usually done in a non-reducing gas atmosphere such as argon, nitrogen, or air.
Perform at 450-850°C. Reduction is usually carried out in a hydrogen stream.
Carry out at a temperature of 400-600°C. [Function/Effect] According to the present invention, first a nickel compound, then a silicon compound, an aluminum compound, and then a chromium compound are sequentially deposited on the surface of α-iron oxyhydroxide particles. When using nickel salt, nickel compound,
Due to the adhesion of the three components of the silicon compound and the aluminum compound, the shape retention of the particles is good over a wide reduction temperature range, and high saturation magnetization can be easily obtained even when the reduction temperature is lowered. Further, the coercive force becomes an appropriate value due to the suppressing effect, and at the same time, the dispersibility is excellent and the corrosion resistance is also improved. This was achieved for the first time by depositing a three-component system of a nickel compound, a silicon compound, and an aluminum compound, and if any one component is missing, the above effect will be insufficient. In particular, when primary aluminum phosphate is used as the aluminum compound, the synergistic effect of the above three components on dispersibility is maximized. That is, it is extremely effective in dispersing ferromagnetic metal fine particles, and ferromagnetic metal fine particles with excellent shape retention of the α-iron oxyhydroxide fine particles without agglomeration between the particles can be obtained. Furthermore, the dispersibility (squareness ratio Rs=(residual magnetic flux density)/(saturation magnetic flux density)) in magnetic tapes is significantly improved. This is presumed to be because phosphate ions act effectively and disentangle the α-iron oxyhydroxide particles, allowing the aluminum compound to adhere uniformly to each α-iron oxyhydroxide particle. However, the exact reason is unknown. This is the reason why an aqueous solution of primary aluminum phosphate is used as the aluminum compound in the present invention. In the present invention, the chromium compound is uniformly deposited on α-iron oxyhydroxide particles for the first time. The uniformly deposited chromium compound imparts appropriate hardness to the ferromagnetic metal particles, and magnetic tapes using these ferromagnetic metal particles have excellent running durability, prevent head clogging, and are suitable for repeated playback and still playback. It is most effective in suppressing output decline in In particular, in order to fully utilize the running durability of the chromium compound, monoaluminum phosphate is the most suitable aluminum compound to adhere to, and the addition of other aluminum compounds will reduce the running durability by half. For this reason as well, an aqueous solution of monoaluminum phosphate is most suitable as the aluminum compound to be added. Furthermore, compared to the conventional method of adding several tens of weight percent of an abrasive material such as aluminum oxide powder at the time of coating to improve running durability, the present invention can be satisfied with the deposition of a relatively small amount of chromium compound. It is extremely advantageous in that it provides still characteristics and at the same time has little dropout and noise. [Example] Examples are shown below. In addition, in the following Examples and Comparative Examples, "%" indicates weight % unless otherwise specified. Example 1 Wet cake of α-iron oxyhydroxide (on a dry basis)
1000g) was put into pure water 20 to obtain an aqueous suspension (slurry) of α-iron oxyhydroxide. Add 40ml of acetic acid (purity 99.5%) to this to adjust the pH of the slurry.
3.20 (20℃). After stirring for 30 minutes, nickel acetate [(CH ₃ COO) ₂ Ni・
4H ₂ O; Nickel content 22.9%] 247 g to 2.3 g of water
An aqueous solution of nickel acetate dissolved in was gradually added.
After stirring for another 30 minutes, add 28% ammonia aqueous solution.
200ml was added to adjust the pH of the slurry to 9.60 (20°C).
After stirring for 30 minutes, the temperature was increased to 90℃.
Aged for minutes. A 28% ammonia aqueous solution was again added to the obtained slurry to adjust the pH of the slurry to 9.4.
Next, 1260 g of an aqueous ortho-silicic acid solution (Si concentration 1%) was gradually added to the slurry while maintaining it at the above-mentioned aging temperature, and the slurry was stirred for 60 minutes. Further, 820 g of a separately prepared aqueous solution of monoaluminum phosphate (Al concentration 1%) was gradually added and stirred for 60 minutes. Thereafter, while maintaining the temperature of the resulting slurry at 90°C, 32 g of chromium acetate [Cr(CH ₃ (COO) ₃ H ₂ O chromium content 20%]) prepared in advance was added to the slurry.
Gradually add an aqueous solution of chromium acetate dissolved in 1.3 parts of water, stir thoroughly and age at 90°C for 60 minutes, then
Cooled to ℃. Separate this suspension and make the cake.
It was dried overnight at 130-135°C to obtain treated dry α-iron oxyhydroxide as shown in Table 1. 500 g of this dry α-iron oxyhydroxide was first heated under an _N2 atmosphere for 600 g.
℃ for 30 minutes, then _H2 flow rate 30/
min, residence time 6 hours, reduced at the temperature shown in Table 1, extracted into toluene, 20℃, relative humidity 60%
The particles were air-dried in a thermostatic chamber for 24 hours to obtain dried ferromagnetic metal particles, and their magnetic properties were measured. The results are shown in Table 1. Furthermore, 12.4 g of a binder consisting of vinyl chloride vinyl acetate copolymer and polyurethane was added to 55 g of the fine particles.
0.7 g of curing agent, 2.8 g of dispersant, and 171 g of a solvent consisting of toluene, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexane were charged all at once into a sand mill and stirred at 1850 revolutions per minute for 2 hours to obtain a paint. This was oriented on a polyester film in a magnetic field of 3000 Gauss to produce a magnetic tape, and its magnetic properties were measured. The results are shown in Table 1.
Next, the produced magnetic tape was packed into an 8 mm video cassette, and Y-S/N was measured using a commercially available 8 mm video tape recorder. A video signal generator and video noise measuring device manufactured by Shibasoku Co., Ltd. were used for signal input and detection. Then, recording and reproduction were repeated, and the number of reproductions until the reproduction output value decreased by 2 dB from the initial output value was determined. The results are shown in Table 1. Examples 2 and 3 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1, except that the amount of the aqueous solution of chromium acetate was changed, and their magnetic properties were measured. The results are shown in Table 1. Further, a magnetic tape was prepared in the same manner as in Example 1, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1. Example 4 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that an aqueous solution of chromium nitrate was used instead of an aqueous solution of chromium acetate, and their magnetic properties were measured. The results are shown in Table 1. Further, a magnetic tape was prepared in the same manner as in Example 1, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1. Example 5 Ferromagnetic metal fine particles were obtained in the same manner as in Example 4, except that the amount of the aqueous chromium nitrate solution added was changed, and their magnetic properties were measured. The results are shown in Table 1. Further, a magnetic tape was prepared in the same manner as in Example 1, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1. Comparative Examples 1 and 2 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that an aqueous solution of chromium acetate was not added, and their magnetic properties were measured. The results are shown in Table 1. In addition, magnetic tapes were prepared in the same manner as in Example 1, except that 5.5 g of chromium oxide powder (Comparative Example 1) or 5.5 g of aluminum oxide powder (Comparative Example 2) was added as an abrasive when making the paint. Measurements of magnetic properties and repeated measurements of Y-S/N were carried out. The results are shown in Table 1. Comparative Example 3 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that the aqueous solution of monoaluminum phosphate was not added, and their magnetic properties were measured. The results are shown in Table 1. Further, a magnetic tape was prepared in the same manner as in Example 1, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1. Comparative Example 4 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that the aqueous solution of monoaluminum phosphate and the aqueous solution of chromium acetate were not added, and their magnetic properties were measured. The results are shown in Table 1. Also, Example 1
A magnetic tape was prepared in the same manner as above, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1. Comparative Example 5 Ferromagnetic metal fine particles were obtained in the same manner as in Example 1 except that an aqueous solution of aluminum sulfate was added instead of an aqueous solution of monobasic aluminum phosphate, and their magnetic properties were measured. The results are shown in Table 1. Further, a magnetic tape was prepared in the same manner as in Example 1, and its magnetic properties and Y-S/N were repeatedly measured. The results are shown in Table 1.

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Claims (1)

[Claims] 1. A suspension (slurry) of an organic acid aqueous solution of α-iron oxyhydroxide fine particles, the slurry having a pH of 4.0.
Add an aqueous solution of nickel salt to the following, then add ammonia to adjust the pH of the slurry to 9.0 to 11.0, and after aging at 70℃ or higher, add ammonia as needed to keep the pH of the slurry at 7.0 or higher. Tsutsu,
Adding an aqueous solution of silicic acid or a silicate and an aqueous solution of monobasic aluminum phosphate to attach a silicon compound and an aluminum compound to the surface of the α-iron oxyhydroxide fine particles to which the nickel compound is attached,
Next, add ammonia as needed to make the slurry.
While keeping the pH at 7.0 or higher, add an aqueous solution of chromium salt to attach the chromium compound to the outermost layer of the α-iron oxyhydroxide fine particles to which the nickel compound, silicon compound, and aluminum compound have been attached, and then add this slurry. Production of ferromagnetic metal fine particles characterized by separately drying to obtain dried α-iron oxyhydroxide to which the nickel compound, silicon compound, aluminum compound, and chromium compound are attached, which is then heated and calcined and then reduced. Method. 2. The aqueous solution of nickel salt is an aqueous solution of an inorganic salt such as nickel sulfate, nickel nitrate, or nickel chloride,
2. The method according to item 1, wherein the aqueous solution is at least one of an organic acid salt such as nickel acetate or nickel oxalate. 3 The aqueous solution of silicic acid or silicate may be an aqueous solution of various silicic acids such as ortho-silicic acid or meta-silicic acid, an aqueous silica sol, an ammonia-stabilized aqueous silica sol, an aluminum-modified aqueous silica sol, or silicic acid. The first method is characterized in that it is at least one kind of aqueous solution of sodium acid.
or the method described in paragraph 2. 4. The chromium salt aqueous solution is at least one of an aqueous solution of an inorganic salt such as chromium chloride, chromium nitrate, chromium sulfate, or chromium phosphate, or an aqueous solution of an organic acid salt such as chromium formate or chromium acetate. The method according to item 1, 2 or 3. 5 Item 1, characterized in that the amount of the aqueous solution of silicic acid or silicate added is 0.5 to 7 parts by weight based on silicon atoms per 100 parts by weight of iron atoms of the α-iron oxyhydroxide. to the method described in any one of paragraphs 4 to 4. 6. Items 1 to 6, characterized in that the amount of the aqueous solution of primary aluminum phosphate added is 0.5 to 7 parts by weight based on aluminum atoms per 100 parts by weight of iron atoms of the α-iron oxyhydroxide. The method described in any of Section 5. 7. Items 1 to 6, characterized in that the amount of the aqueous solution of the chromium salt added is 0.3 to 10 parts by weight based on chromium atoms per 100 parts by weight of iron atoms of the α-iron oxyhydroxide. Any method described.