JPH0727809B2 - Method for producing hexagonal ferrite powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing hexagonal ferrite particle powder mainly used as magnetic powder in a coating type perpendicular magnetic recording medium.

[Outline of Invention]

The present invention is a so-called glass crystallization method in which hexagonal ferrite fine particles are precipitated in a glass matrix. By using potassium borate as a glass-forming substance, the amorphization conditions can be relaxed and the obtained hexagonal crystal can be obtained. It aims to improve the plate-like ratio and squareness ratio of the ferrite particles.

[Conventional technology]

Conventionally, as a magnetic recording / reproducing system for a magnetic recording medium such as a magnetic tape, γ-Fe ₂ O ₃ or cobalt-adhered γ-Fe is used.
_The so-called in-plane recording is generally used in which the magnetic powder consisting of needle crystals such as ₂ O ₃ and CrO ₂ is oriented in the in-plane direction of the recording medium and the residual magnetic ratio in the in-plane direction of these magnetic powders is used. Is.

However, this type of magnetic recording medium has the property that the demagnetizing field in the magnetic recording medium increases as the recording density becomes higher. If this is attempted, the self-demagnetization loss and the recording demagnetization loss may increase, and the recording / reproducing characteristics may deteriorate. When the recording layer of the magnetic recording medium is thinned or the coercive force of the magnetic powder is increased in order to suppress the demagnetization loss, the output of the reproduction signal is reduced, the recording head is saturated, and sufficient recording cannot be performed. There is a problem, and there is a limit to the high density achieved by the in-plane recording.

Therefore, conventionally, a perpendicular magnetic recording system has been proposed which utilizes the residual magnetization in the direction perpendicular to the magnetic layer surface of the magnetic recording medium. It is known that in this perpendicular magnetic recording system, the demagnetizing field in the recording medium decreases as the recording density increases,
It can be said that it is suitable for high-density recording.

Since the magnetic recording medium used in this perpendicular magnetic recording system needs to have an easy axis of magnetization in a direction perpendicular to the surface of the magnetic layer, it is difficult to use a conventional acicular magnetic powder. The use of a so-called metal thin film type magnetic recording medium in which a magnetic recording layer is formed by directly depositing a —Cr alloy or the like on a base film by a vacuum thin film forming technique such as a sputtering method is under study.

However, this type of magnetic recording medium still has problems in practical properties such as running property, durability, and productivity. Therefore, on the other hand, the coating type perpendicular magnetic recording which can be manufactured by the conventional coating method. Development of the medium is also in progress.

As this coating type perpendicular magnetic recording medium, for example, one in which hexagonal ferrite particle powder of the general formula BaFe ₁₂ O ₁₉ or the like is used as the magnetic powder is known. The reason for using the hexagonal ferrite particle powder here is that the plate surface of the hexagonal ferrite particle powder after application is the base because the shape is flat and the easy magnetization axis is perpendicular to the plate surface. This is because it is likely to be parallel to the film surface, and vertical alignment can be easily performed by a magnetic field orientation treatment or a mechanical orientation treatment. Thus, by using the hexagonal ferrite particle powder as the magnetic powder to manufacture a perpendicular magnetic recording medium by a coating method which has been widely used in the past, it is possible to achieve excellent running durability and to cope with perpendicular magnetic recording. It is possible to manufacture the medium with high production efficiency.

By the way, as a method for producing the above-described hexagonal ferrite particle powder, a hexagonal ferrite raw material and a glass-forming substance are mixed and melted to be amorphous, and heat treatment is performed to form hexagonal ferrite fine particles in a glass matrix. A so-called glass crystallization method of causing precipitation is known.

In this case, as previously proposed by the applicant of the present application in Japanese Patent Application No. 59-203595, if sodium borate is used as the glass forming substance, it is not necessary to use a precious metal crucible for melting, Even in the qualitative treatment, it is sufficient to cool under mild conditions such as pouring in water.
Bring great benefits in production.

[Problems to be solved by the invention]

However, when the present inventors further investigated, when sodium borate was used as the glass-forming substance, Na remained in the obtained hexagonal ferrite particle powder, which prepared a magnetic coating. It was found that there is a possibility that NaCl sometimes precipitates on the surface of the magnetic layer by reacting with chlorine Cl in the binder and dispersant. This precipitation of NaCl is not preferable for the recording / reproducing apparatus, and may even deteriorate the electromagnetic conversion characteristics.

Therefore, the present invention has been proposed in order to eliminate such drawbacks, the object is to provide a glass base material without fear of precipitation of NaCl, the conditions of amorphization is mild, the plate An object of the present invention is to provide a production method capable of producing hexagonal ferrite particle powder having an excellent shape ratio.

[Means for solving problems]

The present inventors have completed the present invention by finding that potassium borate is useful as a glass-forming substance, as a result of earnest research over a long period of time without achieving the above-mentioned object, Characterized in that a raw material mixture containing a basic component of crystalline ferrite and potassium borate as a glass-forming substance is melted, rapidly cooled to form an amorphous body, and then the amorphous body is heat-treated. Is.

In the present invention, the composition of the obtained hexagonal ferrite particle powder is represented by the formula AO.nFe ₂ O ₃ (I) (wherein A represents at least one selected from Ba, Sr and Pb). , N is 5 ≦ n ≦ 6) so that the oxides or carbonates (eg α
-Fe ₂ and O _3, BaCO _3, etc.) and the like are mixed at a predetermined ratio, the basic components of the hexagonal ferrite.

Here, a part of Fe in the above formula (I) is replaced with Co, Ti, Mn, Cu, Zn, I
You may substitute by 1 or more types of n, Ge, and Nb. These additional elements are effective in controlling coercive force, grain size, and improving saturation magnetization. For example, Co and Ti are effective in controlling the coercive force of the obtained hexagonal ferrite particle powder, so the substitution amount may be increased or decreased according to the required coercive force.

Further, the plate ratio and the coercive force are improved by substituting a part of Fe of the hexagonal ferrite with at least one of Ge and Mn and Co.

That is, the composition of the hexagonal ferrite particles obtained formula _{BaFe 12-x (Co y M} 1-y) 2x O 19 ... (II) ( where, M in the formula represents at least one of Ge or Mn .) Of each constituent element (Fe ₂ O ₃ , BaO, CoO, Ge
O ₂ and MnO ₂ etc.) are mixed at a predetermined ratio to form the basic component of the hexagonal ferrite, the plate ratio can be about 20, and the coercive force can be suppressed.

Here, Co and M (Ge or Mn) are effective in controlling the coercive force of the obtained hexagonal ferrite particle powder, but when the substitution amount x is less than 0.6, the effect is insufficient and the coercive force is If it exceeds 1.0, on the contrary, if it exceeds 1.0, the coercive force becomes too small. Therefore, in order to use it as a magnetic powder for a magnetic recording medium, in the above formula (II), 0.6 ≧ x ≦ 1.0
It is preferable to adjust the addition amount so that

Further, among the above additional elements, particularly Ge and Mn are effective for controlling the plate ratio of the obtained hexagonal ferrite particle powder, but if the ratio y with respect to Co is less than 0.3, the effect is insufficient and 0.7 If it exceeds, it becomes difficult to control the coercive force, so 0.3
It is preferable that ≦ y ≦ 0.7.

Alternatively, when a part of Fe in the hexagonal ferrite is replaced with Zn and Nb, the saturation magnetization is increased, and the coercive force is controlled at the same time when Co and Ti are replaced. In this case, the composition of the hexagonal ferrite particles obtained formula _{BaFe 12-2a-b (Zn 4a /} 3 Nb 2a / 3) (Co b Ti b) O 19 ... (I
II), oxides of each constituent element (Fe ₂ O ₃ , BaO, ZnO, Nb
₂ O ₅ , CoO, TiO ₂ etc.) may be mixed at a predetermined ratio to form the basic component of the hexagonal ferrite.

Here, when the substitution amount a of Zn and Nb exceeds 0.5, the saturation magnetization σ _s is decreased. On the contrary, when the substitution amount a is less than 0.2, it is difficult to secure a predetermined effect. Therefore, the substitution amount a is preferably within the range of 0.2 ≦ a ≦ 0.5.

Further, Co and Ti have an effect of controlling the coercive force of the obtained hexagonal ferrite particle powder, so the substitution amount b may be increased or decreased according to the required coercive force. If the amount b is less than 0.2, the effect is insufficient and the coercive force becomes too high. On the contrary, if the amount b exceeds 0.5, the coercive force becomes too small. Therefore, in order to use it as a magnetic powder of a magnetic recording medium, in the above formula (III), 0.2 ≦ b ≦ 0.
It is preferable to adjust the addition amount so as to be 5.

Furthermore, when controlling the particle size to be slightly larger (about 0.1 μ) to obtain a hexagonal ferrite particle powder having excellent orientation and dispersibility, the composition of the obtained hexagonal ferrite particle powder Is a general formula Ba _1-d J _d O · n (Fe ₂ O ₃ ) ... (IV) (wherein, J represents at least one of Sr, Ca, and Pb). Elemental oxides (Fe ₂ O ₃ , BaO, SrO, Ca
O, PbO, etc.) may be mixed at a predetermined ratio to form the basic component of the hexagonal ferrite.

Here, Sr, Ca, Pb is effective in controlling the particle size of the obtained hexagonal ferrite particle powder,
If the substitution amount d is less than 0.1, the effect is insufficient, and conversely, if it exceeds 0.8, the particle size becomes too large. Therefore, (I
In the formula V), it is preferable to adjust the addition amount so that 0.1 ≦ d ≦ 0.8. However, when J is Ca, the substitution amount d is preferably 0.5 or less. When the substitution amount d of Ca exceeds 0.5, the saturation magnetization σ _s is reduced.

In addition to the above-mentioned basic components, Co, Ti, Ni, Mn, Cu, Zn,
In, Ge, Nb, etc. may be added to replace a part of Fe with these elements.

On the other hand, potassium borate is used as the glass forming material.
As this potassium borate, K ₂ O ・ B ₂ O ₃ , K ₂ O ・ 2B ₂ O ₃ , K
₂ O ・ 3B ₂ O ₃ , K ₂ O ・ 4B ₂ O ₃ , K ₂ O ・ 5B ₂ O ₃ , 2K ₂ O ・ 5B ₂ O ₃ etc. can be used.

If the ratio of the glass-forming substance to the hexagonal ferrite basic component is too large or, conversely, too small, it may adversely affect amorphization and the properties of precipitated crystals.

For example, the basic components of hexagonal ferrite are Be ₂ O ₃ and B.
Using aO, K ₂ B ₄ O ₇ (= K ₂ O ・ 2B as a glass-forming substance)
_{When 2} O ₃ ) is used, it is preferable to set the mixing ratio of these in the composition range shown by the diagonal lines in FIG. here
If the amount of Fe ₂ O ₃ is too large or the amount of K ₂ B ₄ O ₇ is too small, it becomes difficult to amorphize by, for example, introducing into water. On the other hand, if the amount of K ₂ B ₄ O ₇ is too large or the amount of Fe ₂ O ₃ or BaO is too small, hematite will be precipitated and the crystallinity will be poor, and the yield of hexagonal ferrite will be reduced, which is not preferable.

Then, in the present invention, first, the basic components of the hexagonal ferrite and the glass-forming substance are mixed and melted.

In this case, by using potassium borate as the glass forming substance, the melting temperature at the time of melting can be lowered,
For example, it can be melted using an alumina crucible. That is, a mixture of the basic component of hexagonal ferrite and potassium borate may be placed in a container such as an alumina crucible and heated and melted in the air by a known means such as electric furnace heating.

Next, this melt is rapidly deteriorated to become an amorphous body. For this amorphization, the use of potassium borate as the above-mentioned glass-forming substance relaxes the quenching conditions, and for example, it is possible to adopt a method such as simply pouring it into water or flowing it onto a copper plate.

The obtained amorphous material contains each element that constitutes hexagonal ferrite, but has not yet been crystallized. Therefore, the amorphous body obtained by the rapid cooling is further heat-treated to promote crystallization.

Then, the amorphous body in which the hexagonal ferrite particle powder is crystallized by this heat treatment and the hexagonal ferrite particle powder is deposited is subjected to a dilute acid treatment to dissolve and remove the glass base material to separate the hexagonal ferrite particle powder. Examples of the dilute acid used for the dilute acid treatment include organic acids or inorganic acids such as dilute acetic acid, dilute hydrochloric acid, and dilute nitric acid.

In the glass crystallization method, when extracting the hexagonal ferrite fine particles precipitated after the heat treatment, hot acetic acid is usually used, but in this case, strong irritating odor is prevented and the device is made of an acid-resistant material. Will be required.

Therefore, a washing treatment with hot water having a liquid temperature of 80 ° C. or higher is performed as a primary treatment for melting the glass component, and a washing treatment with cold acetic acid is further performed as a secondary treatment to separate the hexagonal ferrite particle powder. Good. Here, in order to perform sufficient extraction, it is necessary to perform a two-step treatment of hot water and cold acetic acid, and sufficient extraction cannot be performed with only one of them.
The magnetic properties of the obtained hexagonal ferrite particle powder are deteriorated.

Finally, the separated crystals are washed with water and dried to obtain hexagonal ferrite particle powder.

[Action]

In the glass crystallization method, the use of potassium borate as a glass-forming substance relaxes the melting condition and the amorphizing condition. For example, when melting a mixture of the basic component of hexagonal ferrite and the glass-forming substance, it is not necessary to use a precious metal crucible, and an alumina crucible or the like can be used. When the melt is made amorphous,
It may be carried out by a method of submerging into water or a method of flowing onto a copper plate.

Furthermore, since the glass-forming material contains no Na component,
NaCl is not deposited during the production of the magnetic recording medium.

〔Example〕

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

Example K ₂ B ₄ O ₇ 40 mol%, BaO 26 mol%, Fe ₂ O ₃ 34 mol% K
_{2 B 4 O 7 · 4H 2} O, mixture of BaCO ₃ and Fe ₂ O _3, 1200 ℃ in an alumina crucible, melted by heating for 15 minutes.

Next, this melt was put into water to make it amorphous.

After heat treatment at 400 ° C for 4 hours, stir in heated weak acid (20% acetic acid, 80 ° C) to remove glass components and extract crystals, and then wash with water to prepare hexagonal ferrite particles. A powder was obtained.

When the obtained hexagonal ferrite particle powder was analyzed by an X-ray diffraction method, it was confirmed to be a single phase of Ba ferrite.

The saturation magnetization σ _s and the coercive force Hc of the obtained hexagonal ferrite particle powder were measured, and the saturation magnetization σ _s =
58.7 (emu / g), coercive force Hc = 820 (0e), σ _r / σ
_s was 0.39.

Comparative example Li ₂ B ₄ O ₇ 40mol%, BaO 26mol%, Fe ₂ O ₃ 34mol%
_{Li 2 B 4 O 7 · 5H} 2 O, mixture of BaCO ₃ and Fe ₂ O _3, was attempted synthesis of hexagonal ferrite particles by the same method as the following previous embodiment.

However, when the obtained product was analyzed by an X-ray diffraction method, the formation of Ba ferrite was not observed, and LiFe ₅ O
It was confirmed that only ₈ generated.

That is, it was concluded that when lithium borate was used as the glass-forming substance, the hexagonal ferrite particle powder could not be synthesized.

〔The invention's effect〕

As described above, in the present invention, since potassium borate is used as the glass-forming material in the glass crystallization method, the melting temperature is lowered, for example, in an inexpensive crucible such as an alumina crucible without using a precious metal crucible. It becomes possible to melt. At the same time, the amorphization conditions are alleviated, and the amorphization can be achieved by a simple method such as a method of charging into water or a method of flowing on a copper plate instead of the twin roll method. Therefore, it becomes possible to significantly improve the production efficiency of the hexagonal ferrite particle powder.

Further, by using potassium borate as the glass-forming substance, it becomes possible to synthesize hexagonal ferrite particle powder by a production method equivalent to the case of using sodium borate, but here, potassium borate is Na Since it does not contain Na, the adverse effect of residual Na can be prevented.

[Brief description of drawings]

FIG. 1 is a ternary composition diagram showing a suitable composition range when K ₂ B ₄ O ₇ , BAO and Fe ₂ O ₃ are used as raw material components.

Claims (1)

[Claims] 1. A raw material mixture containing a basic component of hexagonal ferrite and potassium borate as a glass-forming substance is melted, rapidly cooled to be an amorphous body, and then the amorphous body is heat-treated. A method for producing a hexagonal ferrite particle powder, comprising: