JPH05214413A - Production of magnetic powder for high-density recording medium - Google Patents

Abstract

PURPOSE:To produce a magnetic powder for the high-density recording medium having high coercive force and dispersibility and excellent corrosion resistance. CONSTITUTION:At least one kind selected from Ni, Cu and Co compds. is incorporated into or deposited on hydrous iron oxide or iron oxide to form the grain. A silicon compd. and/or a phosphorus compd. and an aluminum compd. are deposited on the grain surface and then reduced to obtain a magnetic powder. Consequently, a magnetic powder for the high-density recording medium with the surface potential almost equal to that of aluminum is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of magnetic powder for high density recording media which is excellent in dispersibility and corrosion resistance.

[0002]

2. Description of the Related Art In recent years, magnetic recording media such as magnetic tapes and magnetic disks are required to have higher density and higher output, and accordingly, magnetic powders forming the magnetic layer of these magnetic recording media are miniaturized. The magnetic properties of the powder also tend to have high coercive force and high saturation magnetization. The magnetic powder currently used is made of iron oxide hydroxide or iron oxide, which has high coercive force, as a starting material, and mainly contains silicon compounds and aluminum compounds in order to maintain their shape anisotropy and prevent sintering between particles. The mainstream is obtained by reducing the surface-treated product.

[0003]

As described above, in order to realize high density and high output of the recording medium, it is important to reduce the particle size of the magnetic powder and increase the holding power. Another factor that cannot be forgotten is the dispersibility of magnetic particles. Focusing on this point,
In surface treatment mainly composed of silicon compounds, Japanese Patent Publication 6
A number of methods have been proposed, including 1-18323 and Japanese Patent Laid-Open No. 2-175806, but none of them has been sufficiently satisfied. This is because when the silicon compound is treated, iron oxide is coated with water glass, sodium silicate, etc., so that a large amount of active silanol groups (Si-
This is because OH) is present and the silanol groups cause condensation during dehydration such as drying and annealing to cause interparticle aggregation. This phenomenon becomes more remarkable as the particles become finer and the surface energy increases. On the other hand, when the surface treatment is performed with an aluminum compound, such condensation does not easily occur, and therefore, magnetic powder having excellent dispersibility with less aggregation between particles can be obtained. Further, since many recording media contain alumina particles as abrasives together with the magnetic powder, it is desirable that the magnetic powder used be treated with an aluminum compound whose surface state is close to that of alumina. Further, when attention is paid to the corrosion resistance, the silicon compound treatment is inferior in corrosion resistance to the aluminum compound treatment, and the aluminum compound treatment is desirable also from this point.

However, when the same iron oxide was used as the starting material and the treatment with a silicon compound was compared with the treatment with an aluminum compound, the magnetic properties of the aluminum compound treatment, especially the coercive force, were higher than those of the silicon compound treatment. Much inferior. That is, the treatment with an aluminum compound has a drawback that the holding power is lowered. Therefore, if one wants to obtain higher holding power in the treatment of aluminum compounds,
The particles must be smaller or elongated. However, making the particles smaller or making them elongated tends to cause interparticle agglomeration, which is a negative effect in terms of dispersibility.

[0005] Here, in the report on the conventional treatment of aluminum compounds (Japanese Patent Publication No. 56-28964, Japanese Patent Laid-Open No. 119104/1990), the above-mentioned drawbacks have not been clarified and are still unsolved problems. Further, there are reports that other elements are further added to the aluminum compound to enhance the holding power (Japanese Patent Publication No. 2-71427, Japanese Patent Publication No. 2-107701), which is not suitable from the viewpoint of bringing the surface state closer to that of alumina.

Regarding the corrosion resistance, which is important for magnetic powders, when attention is paid to the decrease in saturation magnetization over time, particles having a high coercive force, that is, fine particles, have a large specific surface area (40 m ² / g or more). Also, the saturation magnetization drastically decreased over time. Among them, the magnetic powder treated with the aluminum compound is relatively stable, but as described above, the coercive force of the aluminum compound treatment is more difficult to obtain than the treatment with other compounds, and the particles are smaller. Therefore, the superiority in dispersibility and corrosion resistance cannot be fully utilized.

Further, when an aluminum compound and a silicon compound are simultaneously deposited, in order to obtain a magnetic powder having a high coercive force and excellent magnetic characteristics, Si is approximately 1 or more in molar ratio with respect to Al. Is required, and the surface condition is not suitable unlike the case where the aluminum compound is treated alone, and the corrosion resistance is inferior to the case where the aluminum compound is treated alone.

The present inventors have completed the present invention as a result of intensive studies to obtain a magnetic powder for a high density recording medium having a high coercive force and a high dispersibility without the above-mentioned conventional problems.

[0009]

That is, according to the present invention, iron oxide hydroxide, or iron oxide containing at least one selected from Ni, Cu and Co compounds, or a silicon compound and / Alternatively, in the method for obtaining a magnetic powder by applying a phosphorus compound and an aluminum compound and reducing the same, after depositing a silicon compound and / or a phosphorus compound, further depositing an aluminum compound, and then reducing. The present invention relates to a characteristic method for producing magnetic powder for high-density recording media.

The present invention will be described in detail below. There is no particular limitation on the hydrous iron oxide and iron oxide as the starting materials, but it is very effective to contain or deposit Ni, Cu, Co, etc. because they promote the reduction, and the amount thereof is relative to Fe. , 0.2 to 20 mol% is desirable.
It should be noted that these compounds may be added at the silicon compound, phosphorus compound deposition treatment stage, or the aluminum compound deposition treatment stage.

As the silicon compound to be deposited next, oxides of silica, hydrous silica, colloidal silica, etc., sodium silicate, potassium silicate, magnesium silicate, calcium silicate, barium silicate, aluminum silicate, etc. Examples thereof include silicate compounds, alkoxides, and organosilicon compounds such as silicone oil.
One or more of these compounds may be used. When depositing these compounds, water glass or the like and various metal salts may be added and reacted to deposit as a silicate compound. Various metal salts include magnesium, calcium,
Examples thereof include sulfates such as aluminum, hydrochlorides, nitrates, oxalates, acetates, and the like, and water-soluble salts are preferable. The amount of these metal salts need not be limited to the stoichiometric amount with silicon, and the element of each metal salt is represented by M, and is 0.05 to 2 with respect to Fe.
Mol% and 0.1-1 mol% are preferable. The amount of silicon compound attached is 0.1 to 3 mol% with respect to Fe as Si,
0.5 to 2 mol% is preferable.

Examples of phosphorus compounds include oxides or sodium phosphate, sodium hexametaphosphate, potassium phosphate, magnesium phosphate, calcium phosphate, aluminum phosphate, zirconium phosphate, chromium phosphate, copper phosphate, nickel phosphate, phosphorus. Examples thereof include phosphate compounds such as cobalt acid and iron phosphate. These compounds are
One or more may be used. When depositing the phosphate compound, phosphoric acid or phosphate and various metal salts may be added and reacted to deposit as the phosphate compound.
As various metal salts, magnesium, calcium, aluminum, zirconium and other sulfates, hydrochlorides, nitrates,
Examples thereof include oxalate and acetate, and water-soluble salts are preferable. The amount of these metal salts need not be limited to the stoichiometric amount with phosphorus, and the elements of various metal salts are represented by M, and the amount of Fe is 0.
05-2 mol%, preferably 0.1-1 mol%.

The amount of the phosphorus compound deposited as P is 0.1 to 3 mol% with respect to Fe, preferably 0.5 to 2 mol%. The silicon compound and the phosphorus compound may be applied individually or both may be applied. It is important to perform the above-mentioned deposition treatment of the silicon compound and the phosphorus compound before the deposition treatment of the aluminum compound, and the effect is not exhibited when the deposition is performed simultaneously with the aluminum compound. For example, when an aluminum compound and a silicon compound are applied at the same time, powder which is satisfactory in magnetic properties is not obtained first, and further good results are not obtained in corrosion resistance. When an aluminum compound and a phosphorus compound are applied at the same time, the magnetic properties are excellent but the corrosion resistance is poor.

However, this is not the case when aluminum phosphate is used for the above-described deposition of the phosphorus compound. In that case, the deposition amount is the element M of the various metal salts described above.
Corresponds to 0.05 to 2 mol%, preferably 0.1 to 1 mol% of Al with respect to Fe. In particular, when a silicon compound is applied, it is important not to dry it until the aluminum compound described below is treated. This is because, as described above, the active silanol groups are condensed and interparticle aggregation occurs.

Examples of the aluminum compound to be deposited next include aluminum nitrate, aluminum acetate, basic aluminum chloride, aluminum hydroxide, sodium aluminate, alumina sol, and aluminum alkoxide. The amount of deposition is 3 to 3 for Al with respect to Fe.
20 mol%, preferably 3 to 15 mol% is desirable. Here, when the deposition amount is small, the silicon compound deposited in the previous step cannot be covered with the aluminum compound, and the surface state is different from that of alumina, which is not preferable. Also, if it is large, it is difficult to be returned, which is unrealistic. Further, the ratio of the deposited amount of the silicon compound and / or the phosphorus compound to the aluminum compound is Si / Al and P as Si /
Al molar ratio is 1 or less, preferably 0.03 to 0.75, P
/ Al molar ratio is 1 or less, preferably 0.03 to 0.75. If the molar ratio is too small, the effect cannot be fully exerted, and it is difficult to obtain a high coercive force. On the other hand, if it is large, the coercive force will be sufficient, but the deterioration characteristics will be poor.

The reduction method is not limited, and a known method may be used. After depositing the silicon compound and / or the phosphorus compound thus obtained,
Further, powder particles mainly composed of hydrous iron oxide or iron oxide coated with an aluminum compound are reduced to have a high coercive force of 1300 Oe or more, which is excellent in dispersibility and corrosion resistance. A magnetic powder is obtained.

[0017]

[Examples] Examples and comparative examples will be shown below. In Example 10, iron oxide hydroxide (goethite) was used as a starting material,
All were the same except for 11 and 12. This iron oxide hydroxide was synthesized by a known method, and Ni was deposited on Fe in an amount of 0.9 mol% in advance to promote reduction. The average major axis diameter thereof was 250 nm, the axial ratio was 10, and the ratio was 10. The surface area is 90 m ² / g. Example 1 Goethite was dispersed in water to prepare a 2 wt% slurry. Water glass (28% Si
0.25 g of O ₂ ) was added with vigorous stirring and PH was added with nitric acid.
Was adjusted to 7, and a silicic acid compound was applied. Next, 4 g of aluminum nitrate nonahydrate was added, pH was adjusted to 7 with sodium hydroxide, and an aluminum compound was deposited.
This was filtered, washed and dried to obtain goethite powder. The Si deposition amount and Al deposition amount of the obtained goethite were 0.5 mol% and 6.5 mol% with respect to Fe, respectively.

This powder is reduced in a hydrogen stream at 460 ° C., cooled after completion of the reduction, and gradually oxidized by gradually changing the ratio of nitrogen to air in the mixed gas of nitrogen and air to obtain the desired magnetic properties. A powder was obtained. The magnetic properties of the obtained magnetic powder are
Hc 1580 Oe, σs 145 emu / g, SQ
It was 0.50. In addition, a part of the obtained magnetic powder was collected and left for 1 week in a constant temperature and humidity chamber at 60 ° C. and a humidity of 90%,
A corrosion resistance test was conducted. The corrosion resistance was evaluated by using the decrease of σs as an index. The reduction rate (hereinafter referred to as deterioration rate) of the obtained powder was 11.0%. In addition, Table-1 shows the results of the following Examples and Comparative Examples together as a list.

An electron micrograph of the obtained magnetic powder is shown in FIG. For comparison, electron microscope photographs of the magnetic powders obtained in Comparative Example 1 and Comparative Example 2 described below are shown in FIGS. 2 and 3, respectively.
Shown in. From this, it is understood that the magnetic powder obtained by the method of the present invention has a high coercive force and is excellent in the dispersibility of particles. Furthermore, 100 parts of the obtained magnetic powder, 20 parts of a binder made of polyurethane, 3 parts of a curing agent, 12 parts of an abrasive (alumina), 3 parts of a dispersant, and 300 parts of a solvent made of toluene and methyl ethyl ketone are mixed in a sand mill. Got the paint. The obtained coating material was applied on a polyester film so that the dry coating film thickness was 4.0 mμ, and after magnetic field orientation, it was dried to obtain a magnetic tape. The characteristics of the obtained magnetic tape were measured with an external magnetic field of 5 kOe. The results are shown in Table-2.

Further, the surface potential of the obtained magnetic powder was measured, and the alumina used as an abrasive for comparison and Comparative Examples 1 and 2 described below were also measured in the same manner. The results are shown in Fig. 4. As shown in FIG. 4, the surface potential of the magnetic powder obtained by the method of the present invention is close to that of alumina, and the surface state is also close to that of alumina. The surface is the same as the surface treated with alumina alone, and the magnetic properties and tape properties are superior to the conventional aluminum compound alone deposition (Comparative Example 2). Comparative Example 1 Goethite was dispersed in water to prepare a 2 wt% slurry. 500 g of this slurry was mixed with water glass (28% SiO 2
₂ ) 2.50 g was added under strong stirring, pH was adjusted to 7 with nitric acid, and a silicic acid compound was adsorbed. This was filtered, washed and dried to obtain goethite powder. The amount of Si deposited on the obtained goethite was 5.5 mol% with respect to Fe.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain a silicon compound-treated magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1610 Oe, σs 1
It was 42 emu / g, SQ 0.51, and the deterioration rate was 25.0%. A magnetic tape was obtained using the obtained magnetic powder in the same manner as in Example 1. The characteristics of the obtained magnetic tape are shown in Table 2. Comparative Example 2 A goethite slurry was prepared in the same manner as in Comparative Example 1, and 500 g of this slurry was added to a sodium aluminate solution (21% Al _2
3 g of O ₃ ) was added under strong stirring, the pH was adjusted to 7 with nitric acid, and the aluminum compound was deposited. This was filtered, washed and dried to obtain goethite powder. The amount of Al deposited on the obtained goethite was 6.5 mol% with respect to Fe.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain an aluminum compound-treated magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1400 Oe, σs
139 emu / g, SQ 0.49, deterioration rate 12.5
%Met. Example 2 A goethite slurry was prepared in the same manner as in Example 1, and 500 g of this slurry was mixed with water glass (28% SiO ₂ ) O. 25
g was added. 0.3g of magnesium nitrate hexahydrate
Was further added, and the pH was adjusted to 7 with nitric acid to deposit a silicate compound. Next, 4 g of aluminum nitrate nonahydrate
Was added and the pH was adjusted to 7 with sodium hydroxide. This was filtered, washed and dried to obtain goethite powder. The deposited amounts of Si, Al and Mg of the obtained goethite were 0.4 mol%, 6.6 mol% and 0.2 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1595 Oe and σs 141 emu.
/ G, SQ 0.50, the deterioration rate was 12.0%. Example 3 All of Example 2 except that 0.3 g of magnesium nitrate hexahydrate of Example 2 was changed to 0.3 g of calcium nitrate tetrahydrate.
Obeyed. The deposited amounts of Si, Al and Ca on the obtained goethite were 0.5 mol%, 6.8 mol% and 0.3 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1590 Oe and σs 140 emu.
/ G, SQ 0.52, deterioration rate was 10.5%. Example 4 Example 2 was followed except that 0.3 g of magnesium nitrate hexahydrate of Example 2 was replaced with 0.4 g of aluminum nitrate nonahydrate. The deposited amounts of Si and Al of the obtained goethite powder were 0.5 mol% and 6.8 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1520 Oe, σs 138 emu.
/ G, SQ 0.49, deterioration rate was 12.5%. Comparative Example 3 A goethite slurry was prepared in the same manner as in Comparative Example 1, and 500 g of this slurry was added with water glass (28% SiO ₂ ) 0.25.
g, and ₃ g of a sodium aluminate solution (21% Al ₂ O ₃ ) were added under strong stirring, the pH was adjusted to 7 with nitric acid, and the silicic acid compound and the aluminum compound were simultaneously deposited. This was filtered, washed and dried to obtain goethite powder. The Si deposition amount and Al deposition amount of the obtained goethite were 0.5 mol% and 6.5 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain a magnetic powder simultaneously treated with a silicon compound and an aluminum compound. The magnetic properties of the obtained magnetic powder are Hc
1410 Oe, σs 140 emu / g, SQ
It was 0.49 and the deterioration rate was 19.0%. Comparative Example 4 A magnetic powder was obtained according to Comparative Example 3 except that the amounts of the water glass and the sodium aluminate solution in Comparative Example 3 were changed to 1.75 g and 1.5 g, respectively. The amount of Si deposited and the amount of Al deposited on the obtained goethite were 3.3 mol% based on Fe,
It was 3.1 mol%.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain a magnetic powder for simultaneous deposition of silicon compound and aluminum compound. The magnetic properties of the obtained magnetic powder are Hc
1500 Oe, σs 139 emu / g, SQ
The deterioration rate was 0.51 and the deterioration rate was 23.0%. Similarly goethite slurry Comparative Example 5 Comparative Example 1 was prepared, added at vigorous stirring aluminum nitrate heptahydrate 3.0g To this slurry 500 g, phosphate dihydrate ammonium 0.1g
Was further added, and the pH was adjusted to 9 with an aqueous sodium hydroxide solution to simultaneously deposit the phosphoric acid compound and the aluminum compound. This was filtered, washed and dried to obtain goethite powder.
The P deposition amount and Al deposition amount of the obtained goethite were 0.6 mol% and 6.7 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain a phosphoric acid compound / aluminum compound co-deposited magnetic powder. The magnetic properties of the obtained magnetic powder are Hc
1580 Oe, σs 140 emu / g, SQ
It was 0.50 and the deterioration rate was 18.5%. Example 5 A goethite slurry was prepared in the same manner as in Example 1, 1 g of trisodium phosphate was added to 500 g of this slurry, and 0.6 g of magnesium nitrate hexahydrate was added under vigorous stirring. Was adjusted to 7 and the phosphate compound was applied. Next, sodium aluminate solution (21% Al
₂ O ₃ ) 3 g was added, pH was adjusted to 7 with nitric acid, an aluminum compound was adhered, and this was filtered, washed and dried to obtain goethite powder. The obtained goethite Al,
The deposited amounts of P and Mg were 6.9 mol%, 1.2 mol% and 1.1 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1570 Oe and σs 142 emu.
/ G, SQ 0.51, and deterioration rate was 13.5%. A magnetic tape was obtained using the obtained magnetic powder in the same manner as in Example 1. The characteristics of the obtained magnetic tape are shown in Table 2. Example 6 Example 5 except that 0.6 g of magnesium nitrate hexahydrate of Example 5 was changed to 0.6 g of calcium nitrate tetrahydrate.
Obeyed. Al, P and Ca of the obtained goethite powder
The deposited amounts of Fe are 6.5 mol% and 1.1, respectively, with respect to Fe.
It was mol% and 0.9 mol%.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1590 Oe and σs 147 emu.
/ G, SQ 0.51, and the deterioration rate was 12.5%. Example 7 Example 5 was followed except that 0.6 g of magnesium nitrate hexahydrate of Example 5 was changed to 0.6 g of ferrous sulfate heptahydrate. The deposited amounts of Al and P of the obtained goethite powder were 6.5 mol% and 1.1 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1530 Oe, σs 146 emu.
/ G, SQ 0.52, deterioration rate was 14.0%. Example 8 All Example 5 was followed except that 0.6 g of magnesium nitrate hexahydrate of Example 5 was changed to 0.8 g of aluminum nitrate nonahydrate. The deposited amounts of Al and P of the obtained goethite powder were 7.8 mol% and 1.1 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the target magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1490 Oe, σs 138 emu.
/ G, SQ 0.48, deterioration rate was 13.0%. Example 9 Example 5 was followed except that 0.6 g of magnesium nitrate hexahydrate of Example 5 was replaced with 2 g of zirconyl nitrate solution (13% ZrO2). Al of the obtained goethite powder,
The deposited amounts of P and Zr were 6.7 mol%, 1.0 mol% and 1.0 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1600 Oe, σs 150 emu.
/ G, SQ 0.49, deterioration rate was 13.0%. Example 10 Goethite synthesized by a known method (the same as in Example 9 but having the same particle shape but not coated with a nickel compound) was dispersed in water to prepare a 2 wt% slurry.
To 500 g of this slurry, 1 g of trisodium phosphate was added, and 0.7 g of nickel nitrate hexahydrate was added under vigorous stirring to deposit a phosphate compound. Next, add ₃ g of sodium aluminate solution (21% Al ₂ O ₃ ) and add P with nitric acid.
The H was adjusted to 7 and the aluminum compound was deposited. This was filtered, washed and dried to obtain goethite powder. The deposited amounts of Al, P and Ni of the obtained powder were 6.7 mol%, 1.2 mol% and 1.9 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1540 Oe and σs 148 emu.
/ G, SQ 0.50, the deterioration rate was 12.5%. Example 11 In the same manner as in Example 10, goethite was dispersed in water to prepare 500 g of a 2 wt% slurry. Water glass (28%
SiO ₂ ) 1.20 g and trisodium phosphate 0.5 g are added, and under strong stirring, 0.4 g of nickel nitrate hexahydrate is added and the pH is adjusted to 7 with nitric acid to remove the silicic acid compound and the phosphorus compound. I put it on. Next, sodium aluminate solution (2
₃ % of 1% Al ₂ O ₃ ) was added, and the pH was adjusted to 7 with nitric acid to deposit an aluminum compound. This was filtered, washed and dried to obtain goethite powder. The deposited amounts of Al, Si, P, and Ni of the obtained powder were 6.6 mol%, 0.3 mol%, 0.6 mol%, and 1.
It was 0 mol%. This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the target magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1530 Oe, σs 1
It was 31 emu / g, SQ 0.50, and the deterioration rate was 13.0%. Example 12 Example 10 was repeated except that 0.7 g of nickel nitrate hexahydrate in Example 10 was replaced with 0.7 g of cobalt nitrate hexahydrate.
Obeyed. Al, P and Co of the obtained goethite powder
The deposited amounts of Fe are 6.4 mol% and 1.4, respectively.
It was 1.8% by mol.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder were Hc 1510 Oe, σs 132 emu.
/ G, SQ 0.49, deterioration rate was 12.0%. Example 13 0.7 g of nickel nitrate hexahydrate of Example 10 was added to copper nitrate 3
All Example 10 was followed except that the hydrate was changed to 0.6 g. The deposited amounts of Al, P and Cu of the obtained goethite powder were 6.7 mol%, 1.3 mol% and 1.8 mol% with respect to Fe, respectively.

This powder was reduced and gradually oxidized in the same manner as in Example 1 to obtain the desired magnetic powder. The magnetic properties of the obtained magnetic powder are Hc 1480 Oe, σs 135 emu.
/ G, SQ 0.49, deterioration rate was 12.5%.

[0037]

[Table 1]

[0038]

[Table 2] From this, the physical properties of the magnetic powder obtained by the method of the present invention formed into a tape are generally excellent, and in particular, the characteristics of the particles obtained by the method of the present invention, that is, high retention and excellent dispersibility, Reflected, the holding power is high and the SFD is low.

[0039]

As described above, the magnetic powder obtained by the method of the present invention overcomes the drawbacks of conventional silicon compound treatments, namely, particle aggregation and corrosion resistance, and also the reduction of holding power, which is a drawback of aluminum compound treatments. It is highly suitable for high-density recording media because it has high holding power and excellent dispersibility, and its surface condition is close to that of alumina, which does not easily agglomerate during coating and has excellent corrosion resistance. There is.

[Brief description of drawings]

FIG. 1 is a transmission electron micrograph (magnification: 40,000 times) showing a particle structure of the magnetic powder obtained in Example 1.

FIG. 2 is a transmission electron microscope photograph (magnification: 40,000 times) showing a particle structure of the magnetic powder obtained in Comparative Example 1.

FIG. 3 is a transmission electron microscope photograph (magnification: 40,000 times) showing a particle structure of the magnetic powder obtained in Comparative Example 2.

FIG. 4 Surface potential of the obtained magnetic powder

[Explanation of symbols]

 〇 Comparative example 1 ◆ Example 1 ● Comparative example 2 ◇ Alumina

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Fujii 635 Sasara, Menaka-cho, Neragi-gun, Toyama Prefecture Nissan Chemical Industry Co., Ltd.Toyama Plant (72) Inventor Kazuhiro Takahashi 635 Sasakura, Menzaka-cho, Women's County, Toyama Prefecture Nissan Chemical Industry Co., Ltd. Toyama Factory

Claims (2)

[Claims] 1. An iron oxide hydroxide or iron oxide containing Ni, C
In the method of obtaining a magnetic powder by applying a silicon compound and / or a phosphorus compound, and an aluminum compound to the surface of particles containing or adhered at least one selected from u and Co compounds, and obtaining a magnetic powder. And / or a phosphorus compound is deposited, and then an aluminum compound is further deposited, and then reduction is performed, and a method for producing a magnetic powder for a high density recording medium. 2. The deposition amount of a silicon compound, a phosphorus compound and an aluminum compound is 0.1 to 3 mol% as Si, 0.1 to 3 mol% as P, and 3 to 20 mol% as Al with respect to Fe. And a Si / Al molar ratio of 1 or less and a P / Al molar ratio of 1 or less.