JPH02149428A - Production of ferromagnetic iron oxide powder for magnetic recording - Google Patents

Abstract

PURPOSE:To enhance saturation magnetization by heat-treating the precursor particles to be converted to maghemite or maghemite particles at the specified conditions in the existence of specified amount of zinc ion. CONSTITUTION:Magnetite particles contg. zinc component or berthollide particles are heat-treated at 400-700 deg.C in the oxidative atmosphere. Further maghemite particles contg. zinc component are heat-treated at 400-700 deg.C in the unreduced atmosphere. Maghemite particles having improved saturation magnetization are obtained by converting crystal of the particles with 2-9 atom weight% zinc ion as Zn/Fe. In this case, after the above-mentioned heat treatment, immersing treatment can be performed in an acidic or alkaline medium. Further the obtained maghemite particles may be coated with cobalt compd. or ferrous compd. together therewith.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for producing ferromagnetic iron oxide powder for magnetic recording, particularly suitable for magnetic recording media for high recording density of audio and images. Regarding.

[Technical background of the invention and its problems]

In recent years, magnetic recording of sound and images, and the miniaturization of playback equipment,
BACKGROUND OF THE INVENTION With the advancement in quality and the significant increase in the processing capacity of magnetic recording information, there is an increasing trend toward higher performance in magnetic recording media such as magnetic tapes, magnetic disks, and magnetic drums. In other words, there is a growing demand for improvements in magnetic properties such as high recording density properties and high output properties, and in conjunction with this, the magnetic particles used in magnetic recording media must be fine particles and In particular, it is required to have high coercive force and large saturation magnetization characteristics.

However, although making the magnetic particles into fine particles is the most effective method for reducing noise, on the other hand, as the particles become fine, a decrease in saturation magnetization cannot be avoided, or in a magnetic layer containing dispersed magnetic particles. This may cause a decrease in the filling rate and orientation of the magnetic particles. Therefore, there is a strong desire to improve the magnetization characteristics (saturation magnetization, residual magnetization, etc.) of magnetic powder so as to satisfy the higher recording density and higher output of the magnetic recording medium. Various methods have been proposed to improve the magnetization properties of magnetic powder for magnetic recording materials. For example, the crystal structure of iron oxide powder is densified by heat treatment to improve transfer characteristics as well as saturation magnetization (for example, JP-A-58-199725), or maghemite particles are coated with a cobalt compound to provide high stability. When creating a magnet, transfer characteristics and saturation magnetization tend to deteriorate due to the adhesion treatment, and for this reason, a combination of a ferrous compound and a zinc compound is applied, or the adhesion treatment is heat-treated. There are known methods for improving the saturation magnetization as well as the transfer characteristics (for example, JP-A-53-87961, JP-A-60-208805, JP-A-61-4202). However, in the former case, when trying to obtain sufficient transfer characteristics, α-Fez03 is likely to be formed and a decrease in saturation magnetization is unavoidable, and in the latter case, a certain level of coercive force and saturation magnetization is required. Although improvements have been made, there are still many problems that require improvement, such as large changes in coercive force over time.

[Summary of the invention]

The present inventors have long been aiming for higher recording density, higher output, and lower noise in the magnetic recording medium, and
We have been conducting various studies to improve the performance of iron oxide magnetic powder, especially acicular maghemite particles, which are used in large quantities today, in order to be applicable to this purpose. Further consideration has been given. As a result, by heat-treating so-called magnetite precursor particles or maghemite particles under specific heating conditions in the presence of a specific amount of specific metal ions, the particle crystals are transformed by the metal ions, resulting in maghemite with high saturation magnetization. The maghemite particles can be made into particles with stable magnetization properties, and these maghemite particles do not cause deformation or sintering of the particle shape, do not substantially lose coercive force, and can be used in media. The material has good dispersibility in the ferrous metal and has an excellent squareness ratio.Furthermore, by coating this material with a cobalt compound or a cobalt compound and a ferrous compound, the magnetic properties of the layer can be improved. It has been found that the present invention is highly suitable for magnetic tapes for high recording densities of sound and images.

That is, the present invention has been achieved based on the above-mentioned knowledge, and the invention described in item 1 provides the following advantages: (a) Magnetite particles or Bertolide particles containing a zinc component are heated to Heat treatment at 700℃ or
or (b) heat-treating maghemite particles containing a zinc component at 400 to 700°C in a non-reducing atmosphere,
A method for producing ferromagnetic iron oxide powder for magnetic recording, characterized in that the particle crystals are modified with 2 to 9 atomic weight % zinc ions as Zn/Fe to obtain maghemite particles with improved saturation magnetization, and , the invention described in paragraph 2 is:
(a) Magnetite particles or Bertolide particles containing a zinc component are heat-treated at 400 to 700°C in an oxidizing atmosphere, or (b) maghemite particles containing a zinc component are heated to 400 to 700°C in a non-reducing atmosphere. Maghemite whose saturation magnetization has been improved by heat treatment at 700°C and immersion treatment in an acidic medium or alkaline medium, so that the particle crystals are transformed into Zn/Fe with 2 to 9 atomic weight % of zinc ions. A method for producing a ferromagnetic iron oxide powder for magnetic recording, which is characterized by obtaining particles of ferromagnetic iron oxide powder for magnetic recording; A method for producing ferromagnetic iron oxide powder for magnetic recording, which comprises applying a cobalt compound or a cobalt compound and a ferrous compound to a product immersed in an acidic medium or an alkaline medium. be.

In the method of the present invention, when (I) zinc component-containing magnetite particles or bertolide compound particles are used as a starting material, the zinc component is added during the production of (a) acicular hydrated ferric oxide. or (b)
Even when added to or deposited on acicular hydrated ferric oxide, or (c)
Even if acicular hydrated ferric oxide is added to and coated on hematite (α-Fe40s) particles obtained by heat dehydration at 300 to 750°C or hydrothermal treatment, it is possible to form (d) hematite. Magnetite (Fe30t) particles or (
e) It may be added to and deposited on particles of a bertholed compound which is an intermediate composition between magnetite and maghemite.

In addition, when adding phosphorus compounds, silicon compounds, aluminum compounds, etc. as sintering inhibitors during the heating dehydration of the hydrated ferric oxide or the reduction of hairatite, it may cause the particle shape to collapse or particle sintering to occur. etc. can be prevented, and the effects of the present invention can be made even more preferable. Further, when (If) maghemite particles are used as a starting material, a zinc component is added and deposited on the particles. Various zinc compounds can be used as the zinc component, and for example, its chloride, sulfate, nitrate, etc. can be used. The amount of the zinc component added is based on the amount of Zn/Fe in the maghemite particles modified by zinc ions, or in the particles after immersing the maghemite particles modified by zinc ions in an acidic medium or an alkaline medium. It is added to the hydrated iron oxide or iron oxide of the object to be treated in an amount of 2 to 9 atomic weight %, preferably 2.5 to 7 atomic weight %. If the amount added is too small than the above range, the desired effect will not be produced, and if the amount added is too much above the above range, the saturation magnetization will decrease. In addition,
In the cases of (b) to (e) and (II) of (1) above, the zinc component addition treatment involves adding a zinc compound to the hydrated iron oxide or an aqueous suspension or wet cake of iron oxide to be treated. , the suspension or wet cake is dried and evaporated to dryness, or a zinc compound is added to the aqueous suspension and an alkali is added to precipitate it as a hydroxide onto the particles to be treated. You may.

Next, in order to heat-treat the magnetite particles or bertolide compound particles containing the zinc component (I) prepared as described above, most commonly, the particles are heated under an oxidizing atmosphere, e.g. 400-700 in air
C., preferably 450 to 650.degree. C., usually for about 0.5 to 5 hours. (n) To heat-treat the maghemite particles containing the zinc component, the temperature is preferably 400 to 700°C in a non-reducing atmosphere, usually in an atmosphere of nitrogen, argon, helium, carbon dioxide, air, etc. 4
This can be carried out by heat treatment at 50 to 650°C for usually about 0.5 to 5 hours. If the heating temperature is too low than the above range, the desired improvement in saturation magnetization will not be achieved, and if it is too high, particle sintering will easily occur and transition to non-magnetic α-Fe, 03 will occur. , which is undesirable because it causes a decrease in saturation magnetization.

Incidentally, the zinc component-containing maghemite particles obtained by oxidizing the magnetite particles or Bertolide particles containing the zinc component (I) above at 400 ° C. or lower are heat-treated in the same manner as in the case of (If) above. It may be applied.

The maghemite particles modified with zinc ions according to the method of the present invention have the (311) plane of the maghemite particles
There was a shift in the lattice constant determined from the linear diffraction angle, which was within 0.3%, and when looking at the intraparticle distribution of zinc ions using the acid dissolution method, it was found that the zinc ions were diffused within the particles.
It can be seen that the particle crystals are maghemite particles modified with zinc ions.

In addition, in the present invention, maghemite is substantially γ
-Fe20. The term also refers to cases that contain a small amount of ferrous iron, such as those that appear to be ferrous.

The ferromagnetic iron oxide powder related to the method of the present invention may be
Non-magnetic components such as unreacted zinc oxide can be removed by immersion treatment in an acidic medium (e.g., aqueous solution of sulfuric acid, acetic acid, etc.) or alkaline medium (e.g., alkaline hydroxide aqueous solution, aqueous ammonia, etc.). By modifying the material, it is possible to reduce the variation in quality, further increase the saturation magnetization, and further increase the coercive force when obtaining cobalt-containing ferromagnetic iron oxide using this material. Can be done.

The above-mentioned zinc ion-modified maghemite particles can be treated with a cobalt compound or a cobalt compound and a ferrous compound on the surface of the particles to make coercive force and saturation magnetization more preferable, if necessary. can. Various known methods can be applied to the adhesion treatment method.

For example, using zinc ion-modified maghemite particles as the base particles, a cobalt compound or a cobalt compound and a ferrous compound are reacted in an alkaline water suspension of the base particles, but the addition method, treatment temperature, alkali concentration, etc. The processing atmosphere can be selected as appropriate. The amount of Co applied is usually 0.5 to 10 atomic weight %, preferably 1 to 8 atomic weight %, and O to 25 atomic weight %, preferably 0 to 18 atomic weight % as Co based on the Fe basis of the base particle. % by atomic weight.

In addition, in the present invention, for example, (1) manganese derived from ferrous sulfate, which is a raw material of goethite, (2) calcium, magnesium, tin, etc. added as a shape regulator of goethite, (3) maghemite. Even if metal ions such as nickel, calcium, and silica which are added to impart thermal stability coexist, the effects of the present invention are not impaired.

The present invention will be further explained below with reference to Examples and Comparative Examples.

[Example of the present invention]

Example 1 Coercive force Hc 330 (Oe), saturation magnetization tr s 71
．． After dispersing 100 g of maghemite (T -FezO+) with a specific surface area of 0 (emu/g) and a specific surface area of 48 (m''/'g) in 2! of water, a 1 mol/1 aqueous solution of zinc sulfate 3 was added under stirring.
2.1m j! was added and the temperature was raised to 60"C. Then 1.
Gradually add ON sodium hydroxide solution to pH 8.
After holding for 2 hours, the mixture was filtered, washed with water, and dried. Next, heat treatment was performed at 500° C. for 1 hour in the atmosphere in a Matsufuru furnace to obtain the desired magnetic iron oxide (Sample A).

Example 2 In Example 1, 1 mol/l zinc sulfate aqueous solution 32.
The desired magnetic iron oxide powder was obtained by the same treatment except that 1 ml was replaced with 53.5 ml (Sample B).

Example 3 In Example 1, 1 mol/l zinc sulfate aqueous solution 32.
The desired magnetic iron oxide powder was obtained by the same treatment except that 1n It was replaced with 74.9m It (Sample C).
.

Example 4 After dispersing 100 g of sample C in a dilute sulfuric acid aqueous solution 21 adjusted to pH 2, the temperature was raised to 40°C with stirring and held for 3 hours, followed by filtration, washing with water, and drying to dissolve unreacted zinc compounds and substances. The target magnetic iron oxide powder was obtained (Sample D).

Comparative Example 1 In Example 1, 1 mol/l zinc sulfate aqueous solution 32.
lnl 10.7nj! A comparative sample of magnetic iron oxide powder was obtained by processing in the same manner except that .

Comparative Example 2 In Example 1, 1 mol/l zinc sulfate aqueous solution 32.
Except for replacing 1mff1 with 128.4mf, the same treatment was carried out to obtain γ-Fez03 modified with zinc ions. Furthermore, 100 g of this magnetic powder was dispersed in a dilute sulfuric acid aqueous solution 21 adjusted to pH 2, and then stirred. The temperature was raised to 40° C. and maintained for 3 hours, followed by filtration, washing with water, and drying to obtain magnetic iron oxide powder as a comparative sample (Sample F).

Comparative Example 3 The starting material T-Fe used in Example 1, 0. was heat-treated in a Matsufuru furnace at 500° C. for 1 hour in the atmosphere to obtain γ-Fe, 01, which was simply heat-treated (Sample G).

Example 5 In Example 2, the heat treatment temperature in the atmosphere was set to 500°C.
The desired magnetic iron oxide powder was obtained by the same treatment except that the temperature was changed to 50°C (Sample H).

Example 6 In Example 2, the heat treatment temperature in the atmosphere was set to 500°C.
The desired magnetic iron oxide powder was obtained by processing in the same manner except that the temperature was changed to 50°C (Sample I).

Comparative Example 4 In Example 2, the heat treatment temperature in the atmosphere was changed to 500°C.
A comparative sample of magnetic iron oxide powder was obtained by processing in the same manner except that the temperature was changed to 00°C (Sample J).

Comparative Example 5 In Example 2, the heat treatment temperature in the atmosphere was changed to 500°C.
A comparative sample of magnetic iron oxide powder was obtained by processing in the same manner except that the temperature was changed to 50° C. (Sample K).

Example 7 Average major axis length 0.2 μm, axial ratio 12, specific surface area 90 m”/
After dispersing 100 g of α-Fe0041 in water 2e, 48.1 m/l of a 1 mol/l zinc sulfate aqueous solution was added under stirring.
and 1 mole/! 12.9 mJ of an aqueous orthophosphoric acid solution was added, and the temperature was raised to 60°C. Next, 1 mole/1 sodium orthosilicate 14.2 mj! Then, an aqueous sodium hydroxide solution of IN was gradually added to adjust pi (7.5), which was held for 2 hours, then filtered, washed with water, and dried. This dried product was heated and dehydrated at 600°C for 2 hours. The zinc-containing magnetite was further reduced at 400°C for 2 hours while flowing hydrogen gas containing water vapor, and then heated in the atmosphere for 50 minutes in a Matsufuru furnace.
A heat treatment was performed at 0° C. for 1 hour to obtain the desired magnetic iron oxide powder (sample L).

Comparative Example 6 A comparative sample was obtained in the same manner as in Example 7 except that the zinc-containing magnetite was heat-treated in the atmosphere at 300° C. for 1 hour in a Matsufuru furnace (sample M).

Comparative Example 7 A comparative sample was obtained by carrying out the same treatment as in Example 7 except that the zinc sulfate aqueous solution was not added (sample N).

Example 8 Average major axis length 0.2 pm, axial ratio 11, specific surface area 50 m”/
After dispersing 100 g of α-Fe00H in water 21, 53.5 n+j of 1 mol/l aqueous zinc sulfate solution was added under stirring.
! was added, and the temperature was raised to 60°C. Thereafter, an aqueous IN sodium hydroxide solution was gradually added to adjust the pH to 8, which was maintained for 2 hours, then filtered, washed with water, and dried. Further, the zinc-containing magnetite was subjected to reduction treatment at 400°C for 2 hours while flowing hydrogen gas containing water vapor, and then heat-treated at 500°C in the atmosphere in a Matsufuru furnace for 1 hour to obtain the desired magnetic iron oxide powder (sample ○).

Example 9 1 mol/l zinc sulfate aqueous solution 410 mj to 1 mol/l ferrous sulfate aqueous solution 201! was added, and the temperature was raised to 50° C. while stirring while blowing nitrogen gas. Next, after adding 1 g of ION sodium hydroxide aqueous solution, nitrogen gas was blown in at 21
After switching to air for 27 minutes and oxidizing for 58 minutes, the precipitate was filtered and washed with water to give 4.8 as Zn/Fe with an average major axis length of 0.25 p m, an axial ratio of 18, and a specific surface area of 95 m''/g.
α-Fe00H containing wt% zinc was obtained. This α
-1 mole/in slurry 211 containing 100 g of Fe00H
2 orthophosphoric acid aqueous solution 12.9m j! After adding
The temperature was raised to 40°C while stirring. Next, an aqueous solution of IN sodium hydroxide was gradually added to adjust the pF to 15, which was held for 2 hours, and then filtered, washed with water, and dried to prepare P/Fe as a heat resistant agent.
Zinc-containing α-
FeOOH was obtained.

This α-Fe00H was dehydrated by heating at 600°C for 2 hours, and then reduced at 400°C for 2 hours while flowing hydrogen gas containing water vapor to obtain zinc-containing magnetite, which was then heated in a Matsufuru furnace at 500°C in the air for 1 hour. Sample P) to be processed to obtain the desired magnetic iron oxide powder.

Comparative Example 8 A comparative sample was obtained in the same manner as in Example 9, except that the zinc-containing magnetite was heat-treated in the atmosphere at 300° C. for 1 hour in a Matsufuru furnace (Sample Q).

Comparative Example 9 The zinc-containing magnetite obtained in Example 9 was heat-treated at 500°C in a nitrogen atmosphere for 1 hour, and then heat-treated at 300°C in the air in a Matsufuru furnace for 1 hour to obtain a comparative sample (sample R).

Example 10 100 g of the magnetic iron oxide powder of sample B obtained in Example 2 was dispersed in 21 ml of water, and 250 ml of an aqueous solution of IOH in sodium hydroxide was added, and the mixture was stirred for 60 ml while blowing nitrogen gas. The temperature was raised to ℃. Then 150 ml of 1 mol/β ferrous sulfate solution! After adding 71 ml of a 1 mol/l cobalt sulfate aqueous solution, the mixture was aged for 5 hours.

The obtained precipitate was filtered, washed with water, and then dried at 120° C. for 5 hours in a nitrogen gas atmosphere to obtain the desired cobalt-containing ferromagnetic iron oxide powder (Sample S).

Example 11 The sample magnetic iron oxide powder obtained in Example 7 was treated in the same manner as in Example 10 to obtain the desired cobalt-containing ferromagnetic iron oxide powder (Sample T).

Example 12 The magnetic iron oxide powder of Sample C obtained in Example 3 was treated in the same manner as in Example 10 to obtain the desired cobalt-containing ferromagnetic iron oxide powder (Sample U).

Example 13 100 g of magnetic iron oxide powder of sample C obtained in Example 3 was dispersed in a 1 mol/l aqueous sodium hydroxide solution 21. The temperature of this material was raised to 40°C under stirring and maintained for 3 hours, followed by filtration, washing with water, and drying.The obtained surface-modified sample was then treated in the same manner as in Example 10 to achieve the desired purpose. A cobalt-containing ferromagnetic iron oxide powder was obtained (sample ■).

Comparative Example 10 The magnetic iron oxide powder of Sample G obtained in Comparative Example 3 was treated in the same manner as in Example 10 to obtain a cobalt-containing magnetic iron oxide powder of a comparative sample (Sample W).

The coercive force (Hc: Oe), saturation magnetization (
σs: emu/g) was measured. These results are shown in Table 1.
Shown below.

In addition, for the samples B, G, S, T, and W, magnetic paints were prepared with the following compositions, and then the magnetic paints were applied onto a polyester film, and dried after orientation to produce a magnetic tape. 10μ).

The coercive force (
Hc), residual magnetic flux density (Br), saturation magnetic flux density (B
m), squareness ratio (Br/8m), orientation ratio (OR), and switching field distribution (SFD) were measured. These results are shown in Table 2.
Shown below.

Magnetic paint composition (1) Magnetic powder (2) Dispersant (3) Vinyl chloride vinyl acetate copolymer synthetic resin (4) Methyl ethyl ketone (5) Toluene Parts by weight Parts by weight Parts by weight Parts by weight Table [Effects of the invention] Book The invention is an industrially easy method to obtain maghemite particles or cobalt-containing maghemite particles with high saturation magnetization and stable magnetization characteristics, and the obtained magnetic powder is suitable for use in magnetic materials for high recording density. It is extremely suitable as a recording material.

Claims (1)

[Claims] 1). (a) Magnetite particles or Bertolide particles containing a zinc component are heated at 400 to 700°C in an oxidizing atmosphere.
or (b) maghemite particles containing zinc component at 400 to 700°C in a non-reducing atmosphere.
A ferromagnetic iron oxide powder for magnetic recording, which is heat-treated to obtain maghemite particles whose particle crystals are modified as Zn/Fe by 2 to 9 atomic weight % of zinc ions and whose saturation magnetization is improved. Production method. 2). (a) Magnetite particles or Bertolide particles containing a zinc component are heated at 400 to 700°C in an oxidizing atmosphere.
or (b) maghemite particles containing zinc component at 400 to 700°C in a non-reducing atmosphere.
and then immersion treatment in an acid medium or an alkaline medium to form particle crystals of 2 to 9 as Zn/Fe.
A method for producing ferromagnetic iron oxide powder for magnetic recording, characterized by obtaining maghemite particles whose saturation magnetization has been improved by being modified by atomic weight percent of zinc ions. 3). Magnetic recording strength, characterized in that maghemite particles with improved saturation magnetization obtained according to claim 1 or claim 2 are coated with a cobalt compound or a cobalt compound and a ferrous compound. A method for producing magnetic iron oxide powder.