JPH0147522B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing iron or magnetic metal powder containing iron as a main component (hereinafter referred to as magnetic iron powder) used as a magnetic recording material such as magnetic tape. More specifically, in a method for producing magnetic iron powder in which iron or an oxyhydroxide or oxide containing iron as a main component (hereinafter referred to as iron oxyhydroxide or iron oxide) is heated and reduced, a suitable acicular form is used. The present invention relates to a method for obtaining magnetic iron powder with excellent magnetic properties. Conventionally, acicular magnetic iron oxide (γ-Fe ₂ O ₃ ) has been mainly used as a magnetic recording material, but in recent years, with the development of magnetic recording equipment, there has been a demand for higher density magnetic recording, and high-resistance materials have been used. There is a demand for magnetic powder with high magnetic force and high magnetic flux density. Acicular magnetic iron powder is known as a magnetic powder that satisfies this requirement. Various methods for producing magnetic iron powder have been proposed, but
The most common method is to thermally reduce acicular iron oxyhydroxide or iron oxide. This method uses fine acicular iron oxyhydroxide or iron oxide with a length of about 0.1 to 1 μm as a raw material, and reduces it while preserving and inheriting its particle shape. Needless to say, at the same time, it is extremely important to prevent loss of acicularity, sintering, and agglomeration during thermal reduction. An object of the present invention is to provide a method for producing magnetic iron powder with excellent magnetic properties by preventing loss of acicularity, sintering, and agglomeration during thermal reduction. Conventionally, various additives such as Si, A
Coatings with inorganic compounds such as , B, Cr, Bi, Ca, etc., and organic compounds such as phenolic resins and higher fatty acids have been proposed. The present inventors obtained the following knowledge in the process of researching a method for preventing the collapse of needle-like properties, sintering, and aggregation caused by this coating method. That is, a method in which iron oxyhydroxide or iron oxide is immersed in an aqueous solution of an inorganic compound such as Si, A, B, Cr, Bi, Ca, etc. and coated by adsorption, or a method in which a neutralization reaction is used to coat with a precipitate. Treatment with inorganic compounds has a strong tendency to cause agglomeration during drying, dehydration, and heating reduction after those treatments, and although it has the effect of maintaining acicularity, the result is a magnetic iron powder that is highly agglomerated. On the other hand, coating with organic compounds such as higher fatty acids is highly effective in preventing agglomeration, but is less effective in preventing the collapse of needle-like properties than coating with inorganic compounds, and coating in large amounts can cause excessive reduction reactions. suppress. Based on these findings, the present inventors have repeatedly investigated the combination of substances, mainly inorganic compounds, that are highly effective in maintaining acicularity, and substances, mainly organic compounds, that are highly effective in preventing agglomeration. For example, if a substance that is highly effective in maintaining acicular properties such as Si, A, and B is coated, and then a substance that is effective in preventing agglomeration such as higher fatty acids is coated, or if the order of coating is reversed, both substances can be further coated. Although various studies have been conducted, such as methods of adding substances simultaneously, no example has yet been found that shows a significant effect in such a simple combination. However, in the course of this research, iron oxyhydroxide or iron oxide was dispersed in an aqueous cationic surfactant solution, and then silicate ions, aluminate ions,
When we investigated the method of adding aqueous solutions such as borate ions, we found that the effects differed greatly depending on the type and combination.When we investigated what caused this difference in effect, we found that the quaternary ammonium salt interface We have discovered a new and completely unexpected finding that the combination of an activator and silicate ions has a great effect on maintaining needle shape, preventing sintering, and preventing agglomeration. Although the reason and mechanism of action cannot be clearly explained, the present inventors believe that quaternary ammonium salt surfactants react with silicate ions and become insolubilized;
Since no insolubilization was observed with other combinations,
The reason for this remarkable effect is that the quaternary ammonium cation groups are close to the particles of iron oxyhydroxide or iron oxide, and the lipophilic groups face outward, allowing the active agent to be uniformly adsorbed. It is also speculated that this is because silicate ions react with quaternary ammonium, insolubilization and fixation to the particle surface occur, and an extremely uniform silicic acid-immobilized surfactant layer is formed. That is, the present invention provides a magnetic iron powder characterized in that particles of iron oxyhydroxide or iron oxide are coated with a quaternary ammonium salt surfactant layer insolubilized and fixed with silicate ions, and then reduced. The present invention provides a method for manufacturing. The present invention will be explained in more detail below. The iron oxyhydroxide or iron oxide in the present invention is
Any needle-like material may be used. For example, various iron oxyhydroxides (α-
FeOOH, β-FeOOH, γ-FeOOH) and their dehydrated iron oxides (α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ ,
Fe ₃ O ₄ ) or these iron oxyhydroxides or iron oxides containing other metals such as cobalt, etc., but the iron oxyhydroxide obtained by wet reaction is not dried, but is made into a water/slurry state. The method used is advantageous. The surfactant used in the present invention is a quaternary ammonium salt surfactant, for example, R-N
(CH ₃ ) ₃ C, R ₂ −N (CH ₃ ) ₂ C, R,
Examples thereof include R'-N( _CH3 ) _2C (R and R' are an alkyl group, a benzyl group, etc.). The amount of quaternary ammonium salt-based surfactant used is not particularly limited as long as it is at least the amount that forms a uniform coating layer and does not affect the reduction reaction during thermal reduction, but the oxywater to be treated 0.3 to 5% by weight based on iron oxide or iron oxide is suitable. There are no restrictions on the silicate ion as long as it is an aqueous solution containing the silicate ion and can be insolubilized and fixed with the quaternary ammonium salt surfactant, but it has the general formula (M ₂ O) _o (SiO ₂ ) _n (M is Na or K,
An aqueous solution of sodium silicate or potassium silicate in which n and m are 1 or 2) is preferably used. The amount used is not particularly limited as long as it is at least the theoretical amount necessary to insolubilize and fix the quaternary ammonium salt surfactant, but the most preferable amount will vary depending on the treatment method shown below. Insolubilization of quaternary ammonium salt surfactants
The method for forming a fixed layer is as follows: (1) Iron oxyhydroxide or iron oxide is dispersed in an aqueous solution of a quaternary ammonium salt surfactant, the active agent is adsorbed onto the particle surface, and then silicate ions are added to make it insolubilized. , fixed. (2) Iron oxyhydroxide or iron oxide is dispersed in an aqueous silicate ion solution, and then a quaternary ammonium surfactant is added to make it insolubilized and fixed. Either method may be used, but method (1) is preferred, that is, a method in which a quaternary ammonium salt surfactant is adsorbed, and then insolubilized and fixed with silicate ions. It is presumed that the slight difference in effectiveness between the two methods is due to slight differences in the uniformity of the coating layer. The most preferable amount of silicate ion used is 1.5 to 4.0 times the theoretically required amount in method (1), and 1.0 times the theoretically required amount in method (2).
~1.2 times the amount. Incidentally, the theoretically necessary amount in the present invention is the amount determined assuming that two quaternary ammonium groups and one SiO ^2/3- group react. The PH value when forming the coating layer is 4th.
There is no restriction as long as the ammonium salt-based surfactant and the silicate ion are each individually soluble in water, but a pH value range of 7.0 to 9.0 is particularly preferable (if there is any effect on the charge and adsorptivity of the particle surface). We assume that there is a relationship). Other processing conditions, such as temperature and amount of water used, are not particularly limited and may be arbitrarily determined based on particle dispersibility, surfactant solubility, etc. The iron oxyhydroxide or iron oxide coated with the silicic acid-immobilized surfactant layer obtained under the above conditions is
It is reduced by a known method at a temperature of 200 to 600°C and becomes an acicular magnetic iron powder with excellent magnetic properties.
Preferably, the reduction is carried out at a temperature of ~500°C. This is because the reduction reaction progresses slowly at temperatures below 300°C, and slightly acicular collapse occurs at temperatures above 500°C. The magnetic iron powder obtained by the present invention has a suitable acicular shape and excellent magnetic properties, and is conveniently used for magnetic recording materials such as magnetic tapes. The present invention will be explained below with reference to Examples. Example,
All parts and % in the reference examples indicate parts by weight and % by weight. Example 1 Adding sodium hydroxide to ferrous sulfate aqueous solution,
100 parts of acicular α-iron oxyhydroxide powder with a major axis of approximately 0.5 μm and a width (minor axis) of approximately 0.04 μm obtained by air oxidation of the generated ferrous hydroxide was mixed with 0.3% stearyl trimethyl ammonium. - Dispersed in 1000 parts of chloride aqueous solution and stirred at room temperature for 2 hours (PH was 7.0). Then, 1.5% sodium silicate (Na ₂ SiO ₃ ).
100 parts of the aqueous solution was added and stirred for an additional hour (in addition,
(PH was 7.2) Then, it was washed with filter and water and dried. The obtained powder was reduced in a glass rotary tube furnace with an inner diameter of 6 cm at 400° C. and a hydrogen flow rate of 3/min for 6 hours to obtain magnetic iron powder. The obtained magnetic iron powder was stabilized by immersing it in benzene. When this magnetic iron powder was observed with an electron microscope, it had a needle-like shape with a major axis of about 0.4 μm and a width of about 0.03 μm, and was free of sintering and agglomeration. The magnetic properties of this powder are coercive force (Hc) 1440 Oe,
Magnetization amount (σs) 161e.mu/g, squareness ratio R = (σr/σs)
= 0.51, which was very excellent. The magnetic properties were measured using a vibrating sample magnetometer with an applied magnetic field of 10 KOe. In other Examples and Reference Examples, all magnetic properties were measured by the above method. Example 2 α-Iron oxyhydroxide powder used in Example 1 100
1 part was dispersed in 1000 parts of a 0.07% sodium silicate aqueous solution, and the mixture was stirred at room temperature for 2 hours. Next, 100 parts of a 3% aqueous stearyl trimethyl ammonium chloride solution was added, and the mixture was stirred for an additional hour, filtered, and dried. The obtained powder was reduced in the same manner as in Example 1 to obtain magnetic iron powder. The magnetic properties of this magnetic iron powder are Hc; 1120 Oe,
σs; 162 e.mu/g, R=0.50. Example 3 The α-iron oxyhydroxide used in Example 1 was heated to 350°C.
was dehydrated to obtain α-ferric oxide (α-Fe ₂ O ₃ ). 100 parts of this α-iron oxide was added to α in Example 1.
- used in place of 100 parts of iron oxyhydroxide, Example 1
A magnetic iron powder was obtained in the same manner as above. The magnetic properties of this magnetic iron powder are Hc; 1370 Oe,
σs; 163e.mu/g, R(σr/σs)=0.50. Reference Example 1 The α-iron oxyhydroxide powder used in Example 1 was reduced under the same conditions as in Example 1 to obtain magnetic iron powder.
This magnetic iron powder has a major axis of 0.1 to 0.3 μm and a width of approximately
It was sintered with broken needles of 0.05 μm, and had severe agglomeration. The magnetic properties are Hc; 420 Oe, σs; 158e.mu/
g, R = 0.19. Reference Example 2 The iron oxide powder (α-Fe ₂ O ₃ ) used in Example 3 was reduced under the same conditions as in Example 1 to obtain magnetic iron powder. Similar to Reference Example 1, this magnetic iron powder is sintered and agglomerated with broken acicularity, and its magnetic properties are Hc: 390 Oe, σs: 159e.mu/g, R=0.18
It was inferior to that. Examples 4 to 6 and Reference Examples 3 and 4 1000 parts of the 0.3% stearyl trimethyl ammonium chloride aqueous solution in Example 1
Table 1 in place of 100 parts of 1.5% sodium silicate aqueous solution
Acicular magnetic iron powder having the magnetic properties shown in Table 1 was obtained by processing in the same manner as in Example 1 using the substance shown in Table 1. Note that the reference example was not subjected to insolubilization or fixation treatment.

[Table] Example 7 100 parts of cobalt-containing α-iron oxyhydroxide powder containing cobalt (Co/Co+Fe=0.15 (atomic weight ratio)) with a major axis of about 0.3 μm and a width of about 0.04 μm was mixed with 0.3% lauryl.
Trimethyl ammonium chloride aqueous solution
The mixture was dispersed in 1400 parts and stirred at room temperature for 2 hours. Then, 120 parts of a 1.5% aqueous sodium silicate solution was added, and the mixture was further stirred for 1 hour, filtered, and dried. The obtained powder was reduced in a glass rotary tube furnace with an inner diameter of 6 cm at 380° C. and a hydrogen flow rate of 3/min for 7 hours to obtain a magnetic iron alloy powder. The magnetic properties of this magnetic iron alloy powder are Hc; 1530
Oe, σs; 172e.mu/g, R=0.48, which was very excellent.

Claims (1)

[Scope of Claims] 1. A method for producing magnetic metal powder in which iron or an oxyhydroxide or oxide containing iron as a main component is thermally reduced, in which particles of the oxyhydroxide or oxide are insolubilized and fixed with silicate ions. A method for producing magnetic metal powder, which comprises coating the powder with a quaternary ammonium salt-based surfactant layer and then reducing the powder. 2. Iron or an oxyhydroxide or oxide containing iron as a main component is dispersed in an aqueous solution of a quaternary ammonium salt surfactant, the surfactant is adsorbed, and then an aqueous solution of silicate ions is added, The manufacturing method according to claim 1, which comprises insolubilizing and fixing. 3 Use 0.3 to 5.0% by weight of quaternary ammonium salt surfactant based on oxyhydroxide or oxide, and use 1.5 to 4.0 times the theoretical amount required to insolubilize the surfactant using silicate ions. The manufacturing method according to claim 2, in which the amount of 4 Adsorption of quaternary ammonium salt surfactant, insolubilization and fixation by silicate ions at pH value 7.0~
9.0. The manufacturing method according to any one of claims 1 to 3, which is carried out within the range of 9.0. 5. The manufacturing method according to any one of claims 1 to 4, wherein the silicate ion is sodium silicate or potassium silicate. 6. The manufacturing method according to any one of claims 1 to 5, wherein the thermal reduction is carried out at a temperature of 300 to 500°C.