JPS6124207A - Manufacture of ferrite powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain hexagonal system ferrite magnetic powder of corpascular state having high saturated magnetization by a method wherein ferrite crystal is grown by performing a heat treatment on the amorphous body obtained from the fused substance of raw material mixture containing raw material component of ferrite and glass forming component, and then the component other than ferrite crystal is removed. CONSTITUTION:The compound ( I ), such as BaO or BaCO3m BaNO3 and the like which can be converted into BaO under the heating condition in the fusing process of raw material mixture, and the compound (II) such as a metal fluoride or chloride selected from a group consistng of Ba, Sr and Pb, are fomed into a ferrite raw material mixture by mixing them at the ratio of 5-55mol% for the total mol quantity of the compounds ( I ) and (II). After said mixture is fused by heating up to 1,250-1,400 deg.C or thereabout, it is cooled rapidly and formed into an amorphous body. Then, a hexagonal system ferrite crystal is grown and deposited from said amorphous body by performing a heat treatment, and then the component other than the ferrite crystal such as glass component and the like is removed by utilizing the treatment such as an etching and the like by an acid, thereby enabling to obtain the ferrite magnetic powder to be used for magnetic recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for producing ferrite magnetic powder for magnetic recording. More specifically, the present invention relates to a method for producing ferrite magnetic powder for magnetic recording suitable for use in perpendicular magnetic recording systems.

[Background of the Invention] Conventionally, magnetic recording has utilized a method of magnetizing a recording medium such as a magnetic tape in the in-plane longitudinal direction. However, in recent years, a perpendicular magnetic recording system has been proposed in order to achieve even higher density magnetic recording, and various magnetic recording media for use in this system have also been studied.

As a method for manufacturing a magnetic recording medium for perpendicular magnetic recording, a method is already known in which a magnetic material layer is formed on a support such as a film by a sputtering method, a vacuum evaporation method, or the like. For example, magnetic recording media have been developed in which a layer of magnetic material such as cobalt chromium is formed on a support by sputtering.

However, the method of manufacturing magnetic recording media using the above-mentioned sputtering method or vacuum evaporation method has higher productivity and product quality than the method of manufacturing conventional magnetic recording media that uses a general coating method. There is a problem that there are some difficulties. Therefore, a method of using a coating method as a method of manufacturing a magnetic recording medium for perpendicular magnetic recording has already been considered.

That is, hexagonal ferrite in the form of hexagonal plate-shaped fine particles (for example, hexagonal barium ferrite) is used as the magnetic powder, and this hexagonal ferrite is mixed and dispersed in a resin (binder).

One method has already been proposed for manufacturing magnetic recording media for perpendicular magnetic recording systems by coating on a support.

Typical manufacturing methods for hexagonal ferrite such as hexagonal barium ferrite used as magnetic powder in the above-mentioned magnetic recording media include coprecipitation, wet methods such as hydrothermal synthesis, and vitrification. It is being

The present invention provides an improved method for producing hexagonal ferrite magnetic powder for magnetic recording using a vitrification method among these production methods.

In general, the production of hexagonal ferrite magnetic powder for magnetic recording by the vitrification method involves melting a raw material mixture containing the desired ferrite component and a glass-forming component, and then rapidly cooling it to form an amorphous body. Hexagonal ferrite crystals are generated and precipitated from the amorphous body by heat treatment in the crystalline state, and then from the substance obtained by the heat treatment (herein referred to as "heat treated product") This is done by a method that removes components other than ferrite crystals. The raw material mixture used to produce hexagonal ferrite magnetic powder for magnetic recording by this vitrification method is generally Ba,
It includes a raw material component of hexagonal ferrite (including a coercive force reducing component) containing a metal atom selected from the group consisting of Sr and Pb, a glass-forming component, and a glass-forming component.

The basic components of the above-mentioned hexagonal ferrite are generally a combination of Fe2O, and a metal oxide such as BaO or 5rO1PbO. Further, as the coercive force reducing component, a combination of an oxide of a divalent metal such as Coo, Ni01ZnO, and an oxide of a tetravalent metal such as TiO2, Zr02, HfO2 is used. The glass-forming component is generally boron oxide (B 20 a ).
is used. However, Ba0 blended in the raw material mixture
Some metal oxides, such as 2SrO1PbO, also function as glass components. Although each raw material component is generally expressed as an oxide, each component is actually introduced into the mixture as other forms of compounds such as various Φ salts that can be converted into the above oxides under the heating conditions of the melting process of the raw material mixture. It is often done.

The ferrite obtained from these raw material mixtures is magnetobranbite-type holehombic ferrite, which generally has the composition formula: RF e 12-2X M z M'
X 0 1g [where, R is a metal atom selected from the group consisting of Ba, Sr, and Pb, and M is Co, Ni, and Zn
M'' is a tetravalent metal atom such as Ti, Zr, Hf, etc., and X is a numerical value in the range of 0.6 to 1.1].

A hexagonal plate-shaped ferrite magnetic powder suitable for use in a perpendicular magnetic recording system is, for example, a fine particle having a hexagonal plate diameter of 0.1 #Lm or less and a thickness of 0.034 m or less. In order to produce such fine-grained magnetic powder, in conventional vitrification methods, for example, a melt of a raw material mixture consisting of the above-mentioned components is rapidly cooled to turn it into an amorphous material. A method is used in which a crystalloid is heat-treated to generate and precipitate hexagonal ferrite crystals.

As a method for rapidly cooling this molten material, a method (referred to as a roll method) is used in which a molten raw material mixture is poured onto the surface of a rotating metal roll and brought into contact with the surface.

As mentioned above, a magnetic recording medium for perpendicular magnetic recording using hexagonal ferrite magnetic powder is one in which a layer containing magnetic powder in which the magnetic powder is dispersed in a binder is formed on a support. be. Of course, it is desirable that this magnetic recording medium generates little noise during magnetic recording and reproduction output, but the degree of noise generated by the magnetic recording medium is related to the particle size of the ferrite magnetic powder used in it. are doing. In other words, in general, the smaller the particle size of the magnetic powder used in a magnetic recording medium, the larger the specific surface area of the particles, the smaller the noise during magnetic recording and reproduction. However, this also applies to coated magnetic recording media using hexagonal ferrite magnetic powder. Therefore,
From the viewpoint of noise reduction during magnetic recording and reproduction output, it is desirable that the hexagonal ferrite magnetic powder used in magnetic recording media has a particle size as small as possible.

When producing hexagonal ferrite magnetic powder by the conventional vitrification method described above, it can be obtained by performing a heat treatment at a low temperature to generate and precipitate hexagonal ferrite crystals from an amorphous body. It is possible to reduce the particle size of ferrite magnetic powder. However, when heat treatment is performed at a low temperature to reduce the particle size of the ferrite magnetic powder, there is a problem in that the magnetic properties of the ferrite magnetic powder, particularly the saturation magnetization, are significantly reduced. In other words, in the case of conventional vitrification methods, the lower the temperature at which the amorphous material is heat-treated, the smaller the particle size of the resulting ferrite magnetic powder becomes, and the saturation of the ferrite magnetic powder decreases accordingly. Magnetization decreases significantly.

Therefore, it is desired to develop a method for producing ferrite magnetic powder that exhibits higher saturation magnetization than that obtained by conventional vitrification methods when comparing the same particle size. In other words, it is desired to develop a method for producing hexagonal ferrite magnetic powder that can obtain ferrite magnetic powder with finer particles than that obtained by conventional vitrification methods when comparing equivalent saturation magnetizations. ing.

[Object of the Invention] An object of the present invention is to provide an improved method that solves the problems in the method of producing hexagonal ferrite magnetic powder for magnetic recording using a vitrification method.

In particular, the present invention provides a method for producing hexagonal ferrite magnetic powder that is in the form of fine particles and exhibits high saturation magnetization.

[Summary of the Invention] The present invention provides non-condensation from a melt of a raw material mixture containing a raw material component of hexagonal ferrite containing a metal atom selected from the group consisting of Ba, Sr, and Pb and a glass-forming component. In a method for producing ferrite magnetic powder for magnetic recording, which comprises obtaining a crystalline body, heat-treating the amorphous body to generate ferrite crystals, and then removing components other than the ferrite crystals from the heat-treated product. , as a compound containing a metal atom selected from the group consisting of Ba, Sr and Pb in the raw material mixture, (I) Ba, S
an oxide of a metal selected from the group consisting of r and Pb, or a compound that can be converted into an oxide of the metal by heating and melting; and

(II) At least one metal fluoride or chloride selected from the group consisting of Ba, Sr, and Pb is used, and the amount of compound (n) used is the same as that of compound (I). ) based on the total molar amount of
The present invention provides a manufacturing method characterized in that the content is in the range of 5 mol %.

The hexagonal ferrite produced by the present invention has finer grains and higher saturation magnetization than that obtained by conventional vitrification methods.

[Detailed Description of the Invention] The present invention relates to a group consisting of Ba, Sr and Pb, which is blended into a raw material for producing hexagonal ferrite magnetic powder for magnetic recording using a conventionally known vitrification method. As a compound containing a metal atom selected from (this compound functions as a constituent of ferrite and a glass component),
It is characterized by using a compound capable of forming an oxide of each metal and a chloride or fluoride of each metal. Therefore, other components other than this component,
That is, other basic components of the hexagonal ferrite, coercive force reducing components, other glass forming components, etc. can be arbitrarily selected based on conventional techniques.

However, preferred raw material mixtures for ferrite in the present invention are: B2011: 20 to 40 mol%; Total sum of the above compounds (I) and compound (II): 25 to 40% by mole;
50 mol%; Fe2O3: 20-50 mo/Iz%; MO [however,
M is at least one divalent metal atom selected from the group consisting of C01Ni and Zn]: 2 to 1O mol%;
and M′O2 [where Mo is Ti, Zr, and H
at least one type of tetravalent metal atom selected from the group consisting of f]: 2 to 10 mol%.

Compounds (I) and (II) in the above raw material mixture
All of the components other than the above are shown as oxides, and their content is also shown as the amount converted to oxides. Other forms of compounds such as various salts can also be used as long as they can be converted into other substances. For example, B2O3 is generally introduced into the feed mixture in the form of boric acid, and other metal components are introduced into the mixture as relatively low melting point compounds, such as carbonates, nitrates, etc. can be introduced into That is, in the present invention, the term B2O3 component is
B20. itself, and contains a substance that can be converted to B2O3 under the heating conditions of the raw material melting process.

Compound (I) used in the present invention has been commonly used as a raw material component for the same type of hexagonal ferrite, and therefore can be used based on conventional techniques. That is, an oxide of a metal selected from the group consisting of Ba, Sr, and Pb or a compound that can be converted into an oxide of the metal by heating and melting [compound (I)]
may be an oxide itself such as Bad, SrO, or PbO, or it may be a carbonate or nitrate of Ba, Sr, or Pb that can be converted into the above-mentioned oxide under the heating conditions of the melting process of the raw material mixture. You can use it as you wish. Further, these compounds may be used alone or in combination of two or more. Particularly preferred compound (I) in the present invention is BaO1 or Ba
Such as COz, HaNO3, etc., can be converted to BaO under the heating conditions of the melting process of the raw material mixture.

The use of compound (I[), -1, i.e., a fluoride or chloride of a metal selected from the group consisting of Ba, Sr and Pb, has replaced a part of compound (I) blended into the raw material mixture in the prior art. It can also be understood as a mode. That is, in the prior art, metal atoms such as Ba, Sr, and Pb were blended into the raw material mixture as oxides or compounds that could be converted into oxides of the metals by heating and melting, but in the present invention, the oxides etc., in which fluoride or chloride is partially replaced.

Examples of fluorides and chlorides that can be used in the present invention include BaF2, SrF2, PbF2 and BaCI
Examples include L2, SrCl2, and PbCfL2. Among them, the former fluoride is stable even at high temperatures, so
Particularly preferred are fluorides and chlorides of barium.These fluorides and chlorides, that is, compound (n), may be used alone or in combination of two or more. It may also be used.

Compound (I) and compound (II) in the above raw material mixture
The ratio of the amount of compound (II) used is
It is necessary that the ratio is in the range of 5 to 55 mol% based on the total molar amount of compound (It), and in particular, the above ratio [1 [/(I + n), molar ratio] is 10 to 50 mol%. The above ratio [II/(
I+II)] exceeds 555 moles, the specific surface area becomes smaller (that is, the particle size becomes larger), and the squareness ratio also deteriorates significantly. On the other hand, the above ratio [1/(I+
(2)] is less than 5 mol %, the effect of introducing fluoride or chloride in the present invention is difficult to be clearly seen.

The manufacturing process of ferrite magnetic powder for magnetic recording using the raw material mixture of the present invention will be described below.

The components constituting the raw material mixture are thoroughly mixed to form a ferrite raw material mixture, and then heated to a temperature near the melting temperature of each component, e.g. 1250 to 1400, according to conventional techniques.
After being heated to about ℃ and melted, it is rapidly cooled to become an amorphous body.

The amorphous body obtained as described above is then heat-treated to produce hexagonal ferrite crystals from the amorphous body, and then ferrite crystals such as glass components are extracted from the heat-treated product. A ferrite magnetic powder for magnetic recording can be obtained by removing other components using a treatment such as etching with an acid.

Note that the heat treatment of the amorphous body to precipitate ferrite crystals is a conventional process, and in the present invention, the amorphous body is heated to 70°C according to the conventional technique.
This can be carried out by heating to about 0 to 950°C.

Fine-grained ferrite crystals obtained by removing components other than ferrite crystals as described above (
Next, the desired magnetic powder (ferrite magnetic powder for magnetic recording) is obtained by washing and drying the ferrite crystal for magnetic recording in the same manner as in the production of hexagonal ferrite crystals with conventional compositions. Obtainable.

In a comparison of equivalent saturation magnetization, non-recording ferrite magnetic powder has a higher magnetization than ferrite magnetic powder produced by a method using only conventional oxides or substances that can be converted into oxides as Ba, Sr, and Pb components. Obtained as fine particles.

In other words, the ferrite magnetic powder for magnetic recording obtained by the present invention has the following characteristics when compared at the same saturation magnetic susceptibility:
The particles are even finer than those obtained by conventional methods. Therefore, magnetic recording media manufactured using the ferrite magnetic powder obtained by the present invention generate less noise during magnetic recording and reproduction output than those manufactured using the ferrite magnetic powder obtained by the conventional method. It is.

Further, since the ferrite magnetic powder for magnetic recording obtained according to the present invention has a high squareness ratio and is composed of ferrite crystals with a clear shape, it is arranged uniformly and orderly in the magnetic powder coating layer. Therefore, a magnetic recording medium manufactured using the magnetic powder has good perpendicular orientation of the magnetic particles and exhibits excellent magnetic recording properties.

For the reasons described above, the ferrite magnetic powder for magnetic recording obtained by the present invention is particularly excellent as a magnetic powder used in a magnetic recording medium using a perpendicular magnetic recording method.

Next, Examples and Comparative Examples of the present invention will be shown.

[Examples 1 to 3] and [Comparative Examples 1 to 2] B20g BaOBaF2-Fe203- as a raw material component system for producing hexagonal ferrite crystals by vitrification method
Coo TiO2 was selected, and the raw materials were weighed and mixed so that each of these components had the following proportions (unit: mol%, total 100 mol%).

B20. : 26.0 mol% BaO: Listed in Table 1 BaF2: Listed in Table 1 Fe2O: 28.8 mol% Coo:' 4.6 mol% TiO2: 4.6 mol% Table 1 BaOBaF2 1i-- (i) (ii) (i) + (eyes) Example 1 32.4 3.6 10 Example 2 zg
, a 7.2 20 Example 3 18.8 18
．． 8 50 Comparative example 136.0 - 0
Comparative Example 2 14.4 21.6 60 Note 2 units are mole % in the raw material mixture The above raw material mixture was placed in a platinum crucible and stirred in a silicon carbide heating element furnace for 3 hours.

The melt is heated to 1,300 to 1,350°C, and then, using air pressure, the melt is poured through micropores onto twin stainless steel rolls rotating in opposite directions, and cooled by contacting them to form a flake-like amorphous material. I got it.

In the heat treatment for ferrite crystal formation/precipitation, the amorphous body is placed in a heat treatment furnace, and the heat treatment furnace is heated to 450 degrees Celsius at a rate of 500 degrees C/hour, and the temperature is maintained for 8 hours until crystallization occurs. 78 at a rate of 300°C/hour
After raising the temperature to 0°C, the temperature was maintained for 8 hours (crystal formation, etc.), and then the temperature was cooled to room temperature at a rate of 100°C/hour.

The heat-treated product obtained as described above was then subjected to etching treatment (treatment for removing glass components, etc.) using acetic acid (35% by volume) at 90°C for 7 hours, and was further washed with water and By performing vacuum drying, fine particulate hexagonal ferrite crystals (ferrite magnetic powder) were obtained.

The obtained hexagonal ferrite crystal was confirmed to be barium ferrite by X-ray diffraction.

Next, regarding the above barium ferrite magnetic powder, coercive force () (c), saturation magnetization, specific surface area, and squareness ratio (δs
/δr) was measured. The measurement results are shown in Table 2.
Among the above measurements, the coercive force, saturation magnetization, and squareness ratio were measured using a vibrating sample magnetometer VSM (manufactured by Toei Kogyo), and the specific surface area was measured using the BET method.

Table 2 Coercive force Saturation Specific surface area Squareness ratio [Hcl Magnetization (Oe) (emu/g) (ni'/g)
(δ g/δ r) Example 1 820 55.6 30.8'O.
4132 785 5B, 0 35.5
0.483' 770 5B, 8 2
5.0 0.45 Comparative Example 1 790 54.4 2B, 2 0
．． 482 580 57.2 13.4
0.37 [Examples 4 to 6] In Examples 1 to 3, BaF2 was changed to BaCJ12 or SrF2, and BaO and BaCl12 or Sr
Fine-particle hexagonal ferrite crystals (ferrite magnetic powder) were obtained in the same manner except that the amount of F2 was changed as shown in Table 3.

Table 3 BaOBaCl2 SrF2 X Example 4 32.4 3.6-10 Example 52B, 8 7.2-20 Example 632:
+ -3,610 Note 2 Units are expressed in mol% in the raw material mixture, and X represents the molar ratio (substitution rate) of BaCu2 (or 5rF2) to BaOxBaCJ12 (or 5rF2).

The obtained nine-hexagonal ferrite crystal was confirmed to be barium ferrite by X-ray diffraction.

Next, regarding the above barium ferrite magnetic powder, coercive force (He), saturation magnetization, specific surface area, and squareness ratio (δS/
δr) was measured in the same manner as in Examples 1-3.

The measurement results are shown in Table 4.

Table 4 Coercive force Saturation Specific surface area Squareness ratio [Hcl Magnetization (Oe) (emu/g) (rn'/g) (δ
s/δr) Example 4 750 55.1 2111.6 0
．． 485 880 58.2 3B, 0
0.476 1180 5B, 0 31
．． 0 0.49 Among the data obtained in Examples 1 to 6 and Comparative Examples 1 to 2, the relationship between specific surface area and saturation magnetization is shown as a graph in FIG. 6 is shown, and black circles show data of Comparative Examples 1 and 2. As is clear from Figure 1, hexagonal barium ferrite magnetic powder produced using a raw material mixture in which a portion of barium oxide is replaced with its fluoride, chloride, or strontium fluoride has both specific surface area and saturation magnetization. It shows a higher value than the hexagonal barium ferrite magnetic powder produced using only barium oxide (Comparative Example 1). On the other hand, when the substitution ratio is too high (Comparative Example 2), the saturation magnetization is high, but the specific surface area is small, that is, the particle size is significantly large.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between specific surface area and saturation magnetization among the data obtained in Examples 1 to 6 and Comparative Examples 1 to 2. White circles indicate data of Examples 1 to 2, and black circles indicate data of Comparative Examples 1 to 2. Patent applicant Fuji Photo Film Co., Ltd. Figure 1 Surface a (m force) Procedural amendment September 7, 1980 Patent application No. 145388 2, Title of invention Method for producing ferrite magnetic powder for magnetic recording 3. Relationship with the person making the amendment Patent applicant name (520) Fuji Photo Film Co., Ltd. 4 Agent address 8 Mitsuya Yotsuya Building, 2-14 Yotsuya, Shinjuku-ku, Tokyo
Level 6, number of inventions increased by amendment None 7,
Subject of amendment Column 8 of the "Detailed Description of the Invention" of the specification, Contents of the amendment As shown in the attached document, the "Detailed Description of the Invention" column of the specification will be amended as follows. Kiichi Supplementary Road 1 - 1 "Hungry Riichi" (1) Page 18, line 5 As fine particles → High saturation magnetization in fine particles

Claims (1)

[Claims] 1. An amorphous material obtained from a melt of a raw material mixture containing a raw material component of hexagonal ferrite containing a metal atom selected from the group consisting of Ba, Sr, and Pb and a glass forming component. In a method for producing ferrite magnetic powder for magnetic recording, which comprises heating the amorphous material to generate ferrite crystals, and then removing components other than the ferrite crystals from the heat-treated product, the raw material is Ba, Sr in the mixture
and a compound containing a metal atom selected from the group consisting of Pb, (I) an oxide of a metal selected from the group consisting of Ba, Sr and Pb, or a compound that can be converted into an oxide of the metal by heating and melting; (II) At least one metal fluoride or chloride selected from the group consisting of Ba, Sr, and Pb is used, and the compound (
A production method characterized in that the amount of II) used is in the range of 5 to 55 mol% based on the total molar amount of compound (I) and compound (II). 2. The amount of compound (II) used in the above raw material mixture is 10 to 4 with respect to the total molar amount of compound (I) and compound (II).
The method for producing ferrite magnetic powder according to claim 1, characterized in that the content is in the range of 0 mol%. 3. The above raw material mixture is B_2O_3: 20 to 40 mol%; total of compound (I) and compound (II): 25 to 50 mol%; Fe_2O_3: 20 to 50 mol%; MO [where M is Co, Ni , and at least one divalent metal atom selected from the group consisting of Zn]: 2-
10 mol%; and M'O_2 [where M' is at least one tetravalent metal atom selected from the group consisting of Ti, Zr, and Hf]: 2 to 10 mol%. A method for producing ferrite magnetic powder according to claim 1 or 2. 4. The method for producing ferrite magnetic powder according to claim 1 or 2, wherein the compound (I) is BaO or a compound that can be converted to BaO by heating and melting. 5. The method for producing ferrite magnetic powder according to claim 1 or 2, wherein the compound (II) is a fluoride or chloride of Ba or Sr.