JPH0459620A - Magnetic powder for magnetic recording and magnetic recording medium therefrom - Google Patents

Abstract

PURPOSE:To obtain the title magnetic powder with reduced variation in coercive force and improved physical properties by forming hexagonal ferrite magnetic powder with a composition containing as substituent elements Nb, Bi, Sb and each specific metallic element. CONSTITUTION:The objective magnetic powder can be obtained by formation with a composition of the formula (M<1> is metallic element selected from Ba, Sr, Pb and Ca; M<2> is metallic element selected from Mn, Mg, Ni, Al, Ce, Cr, Cu, La, V, Ti, Zr and W; a is 8-13; b is 0.01-8; c is 0.3-6; d is 0.01-6; e is 0.01-6; f is number of oxygen atoms satisfying the valences of the other elements). The present magnetic powder is low in the variation in coercive force, excellent in densification with fine average particle size, great in saturation magnetization, and also excellent in dispersibility.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic powder for magnetic recording and a magnetic recording medium, and more particularly to a hexagonal ferrite composed of fine particles suitable for high-density magnetic recording media. This invention relates to magnetic powder and magnetic recording media using the same. A magnetic recording medium having a desired coercive force can be obtained with high precision from the magnetic powder of the present invention.

[Conventional technology]

In recent years, with the demand for higher density magnetic recording.

Perpendicular magnetic recording, which records a magnetic field in the thickness direction of a magnetic recording medium, is attracting attention. The magnetic material used in such a perpendicular magnetic recording medium system must have an axis of easy magnetization in a direction perpendicular to the surface of the magnetic recording medium.

A ferrite with a hexagonal crystal system and uniaxial magnetization anisotropy.

For example, barium ferrite (B a Fe 1201
9) Magnetic powder is a hexagonal plate-shaped crystal with an axis of easy magnetization perpendicular to the plate surface. Therefore, even if the magnetic powder is simply applied, the plate surface will be parallel to the substrate surface. It is suitable as a magnetic material for coating film type perpendicular magnetic recording media because its axis of easy magnetization can be easily oriented in the perpendicular direction by magnetic field orientation treatment or mechanical orientation treatment.

Incidentally, as a coating film type magnetic material for perpendicular magnetic recording, it is necessary not only to have a hexagonal crystal system and uniaxial magnetization anisotropy, but also to satisfy requirements such as first order.

That is, in general, in order to perform recording, reproduction and erasing using a magnetic head on a magnetic recording medium such as a magnetic tape or a floppy disk, the magnetic powder usually has a density of 200 to 2000.
It is necessary to have an appropriate coercive force (Hc) in the range of about [Oe] and a large saturation magnetization (σS) of at least 40 emu/g. Also, the average particle diameter of the magnetic powder is 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 than more.
3μm or less and 0.01μm from the relationship with superparamagnetism
It is necessary that the thickness be within the above range, and furthermore, within this range, it is preferably 0.1 μm or less from the perspective of noise. Moreover, it is important that high output can be obtained when used as a magnetic recording medium, and for this reason it is preferable to use magnetic powder with good dispersibility.6 The dispersibility of magnetic powder in magnetic recording media is 1gi. , determined by the surface properties and the interaction between the magnetic powder and the resin binder, etc.
The quality of dispersibility cannot be sufficiently determined based on the particle shape of magnetic powder alone.

For this reason, generally, magnetic powder is mixed with a resin binder to form a magnetic recording medium, and the quality of dispersibility is evaluated by measuring the glossiness of the surface.

Therefore, it is desirable that the magnetic powder has high gloss when used as a magnetic recording medium.

However, the generally known hexagonal barium ferrite (B a Fe 12019) magnetic powder has a coercive force of nearly 5000 (Oe), which is too large to be used as a magnetic material for magnetic recording, so conventionally, A method of lowering the coercive force by substituting some of the constituent elements of barium ferrite with a substituting element such as cobalt (CO) (for example,
JP-A-56-67904, JP-A-59-1757
No. 07) has been proposed. According to these methods, the coercive force of hexagonal barium ferrite magnetic powder can be reduced by controlling the amount of CO substitution, and the coercive force can be made suitable for magnetic recording media. Publication No. 55-86103).

However, when a CO-containing hexagonal brown barium ferrite magnetic powder whose coercive force is controlled by Co substitution is used for a magnetic recording medium, there is a problem in that the coercive force varies greatly. For example, as shown in Table 1, the coercive force of COO-exchanged hexagonal barium ferrite magnetic powder when used as a magnetic recording medium is approximately 1°1 times or more than the coercive force of the raw material magnetic powder used. There is a problem in that in some cases, it can increase to about 2.0 times.

(Left below) As described above, the coercive force of hexagonal barium ferrite magnetic powder containing substituent elements generally varies when used as a magnetic recording medium, but due to performance requirements such as output and noise,
The permissible range of variation in the coercive force of the magnetic recording medium is the set value ±20 [
It is required that the value be within 0.003, preferably within ±10 (Oe) of the set value. Therefore, in order to manufacture a magnetic recording medium having a coercive force of a desired set value with an accuracy within ±20 (Oe), preferably within ±10 (Oe), it is necessary to determine the coercive force of the magnetic powder used and its Accurately predict in advance the relationship between the coercivity and coercive force when used as a magnetic recording medium, and
! ! Magnetic powders with reasonable coercivity must be produced and used.

This can be explained in detail in Table 1 of JP-A No. 62-207720.
To explain using the example described in the publication, the setting [652 (Oe
) In order to manufacture a magnetic tape with a coercive force of ±20 [Oe], first, the magnetic tape must have a coercive force of exactly 515 ± 15 [Oe].
) It is necessary to produce a Co11-converted hexagonal barium ferrite magnetic powder having a coercive force of

However, the coercive force of Co-containing hexagonal barium ferrite magnetic powder can be controlled by changing the Co content. (Nikkei New Materials, April 28, 1986 issue, p. 52)
Moreover, the coercive force changes considerably even with slight changes in the conditions of the manufacturing process, so it is extremely difficult to stably produce magnetic powder having the desired coercive force within the narrow tolerance range mentioned above. .

Next, even if it is possible to produce magnetic powder with a desired coercive force, the process must be controlled so that the coercive force does not vary significantly when used as a magnetic recording medium. In the case of Co-containing hexagonal barium ferrite magnetic powder, when it is used as a magnetic recording medium, it may vary depending on the moisture content of the magnetic powder, the degree of surface ion concentration 1 dispersion, or changes in conditions in the manufacturing process of the magnetic recording medium. Since the coercive force tends to fluctuate greatly, it is extremely difficult to accurately manufacture a magnetic recording medium having a coercive force exactly as set.

On the other hand, various proposals have been made regarding barium ferrite magnetic powder for high-density magnetic recording media that does not contain -Co.

For example, Sn-containing barium ferrite magnetic powders using tin (S n ) as a substituent element are known, and these magnetic powders have a small temperature dependence of coercive force. However, known CO-free, Sn-containing barium ferrite magnetic powders generally have a large average particle size of 0.85 μm or more, so densification is insufficient, and the plate ratio is large, 10 or more. The inability to obtain a high filling rate in the coating medium (for example, Touhou Review 1 [Volume 40, No. 13, 1985), the large particle size distribution, and the coercive force of 1000 (Oe)
) or less, it is difficult to reduce the coercive force to less than
-900 (Oe)), the saturation magnetization is relatively small, and the dispersibility is poor, so high output cannot be obtained. There is.

For example, Co
Sn-containing barium ferrite magnetic powder that does not contain Sn has an average particle size of 0.2 μm or more.

The plate ratio is also large at 10 or more, and the saturation magnetization is small. Co-free Sn-containing barium ferrite magnetic powder proposed in JP-A-61-219720 can control coercive force as low as 1000 (Oe) or less, but has an average particle size of 0. 1μ
It has the drawbacks of being large, at more than m, and having a large plate-like ratio of at least 10.

Although the Co-free Sn-containing barium ferrite magnetic powder proposed in JP-A-61-295236 has a small average particle size and a low coercive force, it has a large plate-like ratio; The saturation magnetization is 52 (em
It has the disadvantage that it is small, less than 2 u/g.

JP-A-63-193504, JP-A-63-193
Co-free Sn-containing barium ferrite magnetic powder proposed in Japanese Patent Application Laid-Open No. 63-193507 has a small average particle diameter, but a large particle size distribution, and a coercive force of less than 1ooOcOe). g
It has the drawback that it is difficult to reduce the magnetic flux and cannot be used as magnetic powder for magnetic recording media that requires a low coercive force of 200 to 900 (Oe).

In addition, the Co-free Sn-containing barium ferrite magnetic powder proposed in JP-A No. 63-310729 has a small average particle size, a large saturation magnetization, and
Although a product with a low coercive force has been obtained, the average particle size and platelet ratio are large, and the monodispersity is poor, making it undesirable as a magnetic powder for magnetic recording media. As described above, the known CO-free Sn-containing barium ferrite magnetic powder has insufficient performance as a magnetic powder for high-density magnetic recording media.

Barium ferrite magnetic powder using 541 metal selected from Nb, Sb and Ta as a substituting element is also known (for example, Japanese Patent Application Laid-Open No. 193504/1983). However, when these magnetic powders are made into magnetic tape, the coercive force fluctuates greatly, and the temperature dependence of the coercive force also varies from 2 to 2.
4, which is insufficient in terms of the temperature stability of coercive force required of magnetic tapes.

Barium ferrite magnetic powder in which pentavalent metals selected from Nb-5b and Ta are substituted in this way does not have satisfactory characteristics as a magnetic powder for magnetic recording media.

On the other hand, Zr-containing barium ferrite magnetic powder using zirconium (Zr) as a substituent element is known.
For example, JP-A-61-40823, JP-A-63-
156303), and when these magnetic powders are made into a-air tape, the coercive force fluctuates by more than ±30 (Oe) (
JP-A-63-146216*). In the proposal, the Zr-containing magnetic powder has an average particle diameter of 0. Because it is large (1 μm or more), high density is insufficient, and because the plate ratio is large (10 or more), it has the disadvantage that it is difficult to obtain a high filling rate in the coating medium (for example, Toho review j140 volume 1
[No. 13, 1985), and furthermore, since Zr-containing barium ferrite magnetic powder has a large temperature dependence of coercive force (
(For example, Japanese Patent Application Laid-Open No. 193506/1983) is insufficient in terms of the temperature stability of coercive force required of magnetic tapes. As described above, the conventionally known Go-free Zr-containing barium ferrite magnetic powder does not have characteristics that satisfy the required level as a magnetic powder for magnetic recording media.

[Problem to be solved by the invention]

An object of the present invention is to reduce fluctuations in coercive force when used for magnetic recording media such as magnetic tapes.

Another object of the present invention is to provide magnetic powder having excellent physical properties.

Further, the object of the present invention is to control the coercive force within a range suitable for magnetic recording media, to have large saturation magnetization, small average particle diameter, uniform particle size distribution, small platelet ratio, and dispersion. An object of the present invention is to provide hexagonal ferrite magnetic powder with excellent properties.

Another object of the present invention is to provide a magnetic recording medium using magnetic powder having the above-mentioned excellent physical properties.

As a result of intensive research in order to solve the interlayer point of the prior art, the present inventors found that the present invention contains at least one element selected from Nb-B1 and sb, Si, and a specific metal element as a substituent element. The present inventors have discovered that hexagonal ferrite magnetic powder having a specific composition has excellent physical properties that achieve the above object, and have completed the present invention based on this knowledge.

Thus, according to the invention, the general composition formula %formula%) Magnetic powder for magnetic recording represented by

(However, Ml represents at least one metal element selected from Ba, Sr, Pb and Ca, and M2 represents B
1-represents at least one metal element selected from Nb and sb, M3 is Mn-Mg, Ni, AI Ce
, Cr-Cu-La, V-Ti.

Represents at least one element selected from Zr, W and Zn. In addition, a, b-c, de-e and f represent the number of atoms of Fe, Si-M'M2M3 and ○, respectively, + a=8.0~13゜0, b=
o, 01-8. 0-c=0. 3~6.0゜d=
0.01-6. Ol and e=0. 01-6゜0
, and f is the number of oxygen atoms that satisfies the valences of other elements. Furthermore, according to the present invention, by using the magnetic powder for magnetic recording, a magnetic recording medium having a desired coercive force can be manufactured accurately and stably.

The present invention will be explained in detail below.

The feature of the magnetic powder of the present invention is that by controlling the type and proportion of each metal element, the coercive force of the magnetic powder can be increased to 200%.
It can be set to a desired value between ~2000 [Oe], and the coercive force when used as a magnetic recording medium is almost the same as the coercive force of the raw magnetic powder, and the variation in coercive force is extremely small.
A magnetic recording medium having a desired set coercive force can be obtained with high precision.

Furthermore, the magnetic powder of the present invention has a saturation magnetization of 55 emu/g.
The average particle size is 0.08 μm or less, the platelet ratio (long axis diameter of platelet particles/thickness of platelet particles) is 8 or less, and the particle size distribution expressed by the number-based geometric standard deviation is 3.3 or less, has excellent dispersibility, and has excellent physical properties as a magnetic powder for magnetic recording media.

〔composition〕

The magnetic powder of the present invention is a substituted hexagonal ferrite having a composition represented by the above general compositional formula.

In the present invention, the number of atoms of each component element of the magnetic powder is a −
It is necessary that f be within the above numerical range; outside this range, it is difficult to obtain magnetic powder with coercive force, saturation magnetization, and average particle size of 0.08 μm or less suitable for magnetic recording media.

The preferred proportions of each component are as follows in the general compositional formula:
a=9. 0-12. 0-b=0. 02~6°0, c=0. 3-4. 0, d=0. 02-4.
0 and e=0.02 to 4.0, and f is the number of oxygen atoms satisfying the valences of other elements.

Moreover, -M3 is selected from the above-mentioned specific metal elements, and among them, Mg, Ni, Zn, Zr, and combinations thereof are preferable.

The magnetic powder of the present invention may contain particles that do not necessarily exhibit normal hexagonal plate-shaped crystals due to differences in IL manufacturing conditions, etc., but as long as it satisfies the general compositional formula described above, the magnetic powder of the present invention may be used. It can be suitably used as magnetic powder.

[Method for manufacturing magnetic powder]

The method for producing magnetic powder of the present invention is not particularly limited, and for example,
It can be obtained by any production method such as a coprecipitation method, a flux method, a glass crystallization method, and a hydrothermal synthesis method. Among these, the coprecipitation method is particularly preferred because it allows for very good mixing of each component, provides uniform ferrite, and can be converted into ferrite at a relatively low temperature.

Regarding the case where the magnetic powder of the present invention is manufactured by coprecipitation method,
This will be explained below.

Raw material compounds for each metal element include oxides, oxyhydroxides, hydroxides, ammonium salts, nitrates, sulfates, carbonates, organic acid salts, halides, salts such as alkali metal salts, free acids, and acid salts. Examples include anhydrides and condensed acids. Among these, water-soluble compounds are particularly preferred.

The raw material compounds of each metal element are preferably mixed and dissolved in water to form an aqueous solution. Further, if it is convenient to mix and dissolve in an alkaline aqueous solution, it can be mixed and dissolved in an alkaline aqueous solution, which will be described later.

In addition, raw material compounds of metal elements that are difficult to dissolve in water, such as Nb, Bi, or sb, should be dissolved in advance in a solvent such as alcohol, carbon tetrachloride, ether, acetone, chloroform, or an aqueous solution of hydrochloric acid or tartaric acid. It is preferable to use it.

On the other hand, the alkaline components used in alkaline aqueous solutions include:
Any water-soluble material may be used, and examples thereof include alkali metal hydroxides, carbonates, ammonia, and ammonia carbonate.

Specifically, 1, for example, NaOH, Na 2COs-N
a HCO3, KOH-K2C03, NH4
0Hl (N Ha ) CO3, etc. are used, and among these, it is particularly preferable to use a hydroxide and a carbonate salt in combination.
A solution of b and a suitable solvent and an aqueous alkaline solution are mixed to form a coprecipitate at pH 5 or higher, preferably at pH 8 or higher. The obtained coprecipitate is washed with water and then filtered. The cake-like or slurry-like coprecipitate thus obtained is dried at 600-1100°C for 10 minutes to 3 minutes.
Hexagonal ferrite magnetic powder is obtained by firing at a high temperature for 0 hours.

In addition, when the coprecipitate is fired in the presence of flux (fluxing agent), water-soluble flux (for example, alkali metal halides such as sodium chloride and potassium chloride; barium chloride, etc.) is added to the washed coprecipitate. A suitable amount of halogenated alkaline earth metal salts such as strontium; sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, and mixtures thereof, etc.) is added, or a coprecipitate obtained from a mixture of an aqueous metal ion solution and an aqueous alkali solution is added. After adjusting the pH to 1III with hydrochloric acid, etc., filter it, evaporate the water without washing with water, dry it, and heat it at 600 to 1100°C for 10 minutes.
After firing at a high temperature for 30 minutes to 30 hours, the water-soluble flux is washed and separated with water or an acid aqueous solution, further washed with water if necessary, and then dried to obtain hexagonal ferrite magnetic powder.

The magnetic powder of the present invention can be applied to a base material by a conventional coating method using a resin binder to form a magnetic recording medium such as a magnetic tape.

〔Effect of the invention〕

According to the present invention, since fluctuations in coercive force when used as a magnetic recording medium are extremely small, magnetic recording media having a desired coercive force can be stably produced with an accuracy of within ±10 [Oe] of the set value.
can be built. In addition, the coercive force of magnetic powder is 200~
Since the desired value can be set between 2000 [Oe], magnetic powder having a coercive force suitable for general-purpose magnetic heads can be easily obtained. Therefore, a magnetic recording medium having a desired coercive force can be manufactured with high precision. Furthermore, since the particles are fine with an average particle diameter of 0.08 μm or less, they are excellent at high density, and the plate ratio is 8 or less, especially a plate ratio as small as 2 to 5. Since the particle size distribution expressed by the geometric standard deviation is 3.3 or less, a high filling rate can be obtained in the coating medium, and a magnetic powder with high saturation magnetization and excellent dispersibility can be obtained.

These excellent properties are surprising effects that could not be expected from the known Co-containing orthogonal ferrite magnetic powder, Sn-containing hexagonal ferrite magnetic powder, or Zr-containing hexagonal ferrite magnetic powder.

〔Example〕

The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

<Methods for measuring physical properties, etc.> Methods for measuring various physical properties in Examples and Comparative Examples are as follows.

Using a VSM (vibration magnetometer), the maximum applied magnetic field 1
0 (KOe), measured at a measurement temperature of 28°C.

4008 from a photograph of magnetic powder obtained with a transmission electron R microscopy
The maximum diameter of the particles and the ratio of maximum diameter to maximum thickness were measured and calculated by the arithmetic mean.

σ d The above particle diameter values were arranged and determined using a log-normal distribution.

100 parts by weight of magnetic powder sample was mixed with a magnetic tape binder (M
Mix well with 10 parts by weight of R-110 Nippon Zeon (IK) and a mixed solvent consisting of methyl ethyl ketone, toluene, and cyclohexanone to make a magnetic paint, apply this to a polyester film with a doctor blade, and after drying,
After forming a magnetic sheet, the coercive force in the in-plane direction of the magnetic sheet was measured using a VSM (vibrating magnetometer) at a maximum applied magnetic field of 5 [KOe]. The glossiness was measured at an incident angle of 60' using a gloss meter manufactured by Murakami Color Research Institute.

The atomic ratio of each element at the time of raw material preparation was used. Note that the representation of oxygen in the magnetic powder components has been omitted for the sake of brevity.

[Example 1] B a C02.2 H2O 0.3 mol, F e C
13.6 H2O2, 675 mol, NiCl2.6
175 moles of H200 were mixed and dissolved in 2.51 moles of pure water to form a solution A. Further, 0.15 mol of NbCl5 was dissolved in advance in 0.31 mol of ethanol, and this solution was mixed with the above-mentioned liquid A.

NaOH 10.0 mol, Na2CO3 2-5 mol, N
a2s i 03-9 0.2 mol of H2O, 2.5
1 was dissolved in pure water, and this was used as Solution B.

Keep both liquids A and B at 30°C, then mix both liquids and heat to 30°C.
The mixture was stirred for 13 hours. To the thus obtained mixed solution containing the coprecipitate, 5500 ml of IN hydrochloric acid and 501 ml of pure water were added, and the mixture was stirred at 30° C. for 15 hours.

Next, the mixed liquid is separated and the water content of the solids is evaporated to dryness.
It was fired in an electric furnace at 895°C for 2 hours. After washing the obtained fired product with pure water until all soluble materials are removed,
ri'i was dried to obtain ferrite magnetic powder. The physical properties of the obtained ferrite magnetic powder are shown in Table 2.

[Examples 2 to 33] Ferrite magnetic powders listed in Table II2 were produced in the same manner as in Example 1 except that the Ml, M2, and M3 components were changed and the composition ratio was changed.

Note that chloride was used as the raw material for the M1 and M2 components, and among the raw materials for the M3 component, nitrates were used for A1, La, and Mn, and ammonium salts were used for (2) and W. Chloride was used as the raw material for other components. As is clear from Table 2, the magnetic powder of the present invention has an appropriate coercive force, and when formed into a magnetic sheet, the variation ratio of the coercive force is small.

In addition, the average particle diameter is 0.08 μm or less, the platelet ratio is 8 or less, and the particle size distribution is 3.3 or less, and the glossiness of the sheet, which is an indicator of dispersibility, is 90% or more, and it has excellent properties in all respects. shows.

(Left below) [Comparative Example 1] Na25iO+・9H20 was not dissolved. Ferrite magnetic powder was produced in the same manner as in Example 1 under other conditions.

Table 3 shows the composition and physical properties of the obtained magnetic powder.

[Comparative Examples 2 to 33] By changing Ml, M2, and M3 components and composition ratios,
The ferrite magnetic powders listed in Table 3 were manufactured using the same method as in Example 1 under other conditions.

(Left below) [Examples 34 to 40] Ferrite magnetic powder shown in Table 4 was dissolved by dissolving the M2 component using various solvents listed in Table 4, and other conditions were the same as in Example 1. Manufactured.

(Margin below)

Claims (2)

[Claims] (1) General compositional formula (Fe)_a(Si)_b(M^1)_c(M^2)_
Magnetic powder for magnetic recording represented by d(M^3)_eO_f. (However, M^1 represents at least one metal element selected from Ba, Sr, Pb, and Ca, M^2 represents at least one metal element selected from Bi, Nb, and Sb, and M^ 3 is Mn, Mg, Ni, Al, C
e, Cr, Cu, La, V, Ti, Zr, W and Zn
Represents at least one element selected from. Also,
a, b, c, d, e and f are respectively Fe, Si,
Represents the number of atoms of M^1, M^2, M^3 and O, a
=8.0-13.0, b:0.01-8.0, c:0.
3-6.0, d: 0.01-6.0, and e=0.0
It takes a value of 1 to 6.0, and f is the number of oxygen atoms that satisfies the valences of other elements. ) (2) A magnetic recording medium using the magnetic recording magnetic powder according to claim 1.