JPH05174359A - Magnetic powder for magnetic recording and magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide magnetic powder by which a coasting material is easily available comparing with the conventional material, sine the dispersibility is very excellent, and whose output, and S/N characteristics are superior, and which is very efficient to a high density. CONSTITUTION:The magnetic power for magnetic recording incorporates the water contents of from >=1.35X10<-4>x SBET (g) to <=4.3X10<-4>XSBET (g) per unit mass, when a specific surface area measured by a BET method using gaseous nitrogen is SBET(m<2>/g), and also is larger than 800(Oe) in the coercive force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder for magnetic recording suitable for high density recording, and a magnetic recording medium.

[0002]

2. Description of the Related Art A magnetic recording medium manufactured by coating is
It is composed of a supporting base made of polyethylene terephthalate or the like, and a magnetic layer containing magnetic powder and binder resin as main components formed on the supporting base.

Magnetic powders used in magnetic recording media are conventionally γ-Fe ₂ O ₃ , Co-deposited γ-Fe ₂ O ₃ ,
Needle-shaped magnetic powders such as Co-doped γ-Fe ₂ O ₃ , Co-deposited Fe ₃ O ₄ , and metallic Fe have been used, and an in-plane recording method using magnetization in the in-plane longitudinal direction has been adopted. However,
This in-plane recording method is not suitable for high-density recording / reproducing because the influence of the demagnetizing field increases as the recording density increases.

Therefore, in recent years, a perpendicular magnetic recording system has been proposed which uses magnetization in the direction perpendicular to the surface of the magnetic layer. This perpendicular magnetic recording system, with the increase in recording density,
It can be said that this magnetization is the most suitable recording method for high-density recording because its magnetization becomes more stable.

As a magnetic recording medium suitable for such a perpendicular magnetic recording system, a Co--Cr alloy or the like is deposited on a supporting substrate using a vacuum technique such as a vacuum deposition method or a sputtering method, or a plate surface It is known to apply hexagonal ferrite powder having an easy axis of magnetization in the vertical direction.

The magnetic recording medium using the vacuum technique is mass-producible,
Although it has various problems such as manufacturing cost, the coating type magnetic recording medium is very promising because conventional manufacturing facilities can be used and mass productivity is excellent.

Hexagonal ferrite powder used for such a coating type magnetic recording medium is, for example, M type Ba powder.
Fe ₁₂ O ₁₉ , W-type BaMe ₂ Fe ₁₆ O ₁₇ (Me is a substitution metal element), or hexagonal ferrite powder in which some of those atoms are substituted with other elements, or a composite of M-type and W-type Powders, composite powders of M type and spinel, etc. are known and are being researched and developed.

[0008]

By the way, when acicular magnetic powder or hexagonal ferrite powder is used as a component of the magnetic recording medium, the magnetic agglomeration of the particles is strong and it is necessary to discontinue the magnetic agglomeration. is there.

For this purpose, it becomes necessary to disperse the particles by applying a large amount of beads to the sand grinder, increasing the non-volatile content, introducing a kneader, and the like to apply high shear. ..

In particular, hexagonal ferrite powder having an axis of easy magnetization in the direction perpendicular to the plate surface is more magnetic than needle-like magnetic powder because the particles are in contact with each other in the plane as compared with the conventional needle-like magnetic powder. It has a problem that it is hard to disperse when it is made into a paint because it is strongly aggregated.

The present invention has been made to solve the above problems, and provides a magnetic recording magnetic powder and a magnetic recording medium which can be easily dispersed by including a certain range of water in the magnetic recording magnetic powder. It is intended to be provided.

[0012]

The magnetic powder for magnetic recording of the present invention has a specific surface area of SBET (m ² ) measured by the BET method using nitrogen gas. / G), 1.35 × 10 ⁻⁴ × SBET (g) or more per unit mass, 4.3 × 10 ⁻⁴
× SBET (g) Containing water or less and coercive force of 80
It is characterized by being larger than 0 (Oe).

In the magnetic recording medium of the present invention, the specific surface area measured by the BET method using nitrogen gas is SBET (m
² / G), 1.35 × 10 ⁻⁴ per unit mass
A magnetic layer containing magnetic powder having a coercive force of more than 800 (Oe) and containing water of not less than × SB ET (g) and not more than 4.3 × 10 ^-4 × SBET (g) in a resin. It is characterized by having.

[0014]

The magnetic powder for magnetic recording of the present invention has a specific surface area of SBET (m ² /
g), 1.35 × 10 ⁻⁴ × per unit mass
It contains water of SBET (g) or more and 4.3 × 10 ⁻⁴ × SBET (g) or less. Here, the amount of water per unit mass is regulated within this range is 1.35 × 10 ⁻⁴ ×
If it is less than SBET (g), the magnetic powder cannot be easily dispersed. Therefore, 2.7 × 10 ⁻⁴ × SBET (g) or more is more effective. It is considered that when the water content is small, the water has little effect of weakening the magnetic cohesion of the particles, and the viscosity increase due to water cannot be expected in the dispersion step at the time of forming the coating material.
On the other hand, if it is more than 4.3 × 10 ⁻⁴ × SBET (g), the curing agent consumption rate is increased and the stability of the coating composition is impaired. The magnetic powder for magnetic recording of the present invention has a coercive force of 8
It is an essential requirement that it is larger than 00 (Oe). When the coercive force of the magnetic powder for magnetic recording is 800 (Oe) or less, it is difficult to apply it to the high-output, high-density magnetic recording medium aimed at by the present invention, and the effect of the present invention is not clearly exhibited.

Specific surface area SBE of magnetic powder for magnetic recording of the present invention
Whatever T is, the effect of the present invention can be obtained by including the water in the above range. In particular, its specific surface area SBET is 35 m ² / G or more 65m ² It is desirable to satisfy the range below / g. This is the specific surface area S
BET is 35m ² If it is less than / g, it is difficult to obtain a medium having high surface smoothness, so that high output cannot be obtained, and since the particles are large, medium noise is high. On the other hand, specific surface area SBET
Is 65m ² If it is larger than / g, the cohesion of the particles is so strong that they are difficult to disperse and the medium noise is high, and the magnetization of the magnetic powder is small, and it is difficult to obtain a medium having a high output.

As the magnetic powder for magnetic recording of the present invention, hexagonal plate-shaped hexagonal ferrite powder can be used. As the hexagonal ferrite powder, in order to obtain sufficient recording / reproducing and obtain a high S / N in a region where the recording wavelength is 1 micron or less, where perpendicular magnetization recording is more significant than in-plane recording, It is preferable that the particle size is 0.01 to 0.3 micron and the particle size is uniform.

As hexagonal ferrite powder, M type, W type
Barium or strontium ferrite having a crystal structure such as a mold, or spinel-coated or spinel-containing barium ferrite or strontium ferrite can be used.

[0018]

The present invention will be described in detail below with reference to specific examples and comparative examples. The magnetic properties, the specific surface area, the water content, and the curing rate of the coating material of the magnetic powder prepared for this example were measured in an environment kept at the same temperature and humidity as in the vessel atmosphere. (Specific example 1)

First, Co and Ti are formed by a glass crystallization method.
And Sn-substituted Ba ferrite magnetic powder were prepared. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen.

Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. The magnetic characteristics of the magnetic powder for magnetic recording were measured by using a vibrating sample magnetometer (VSMP-1) manufactured by Toei Industry Co., Ltd., and as shown in Table 1, a coercive force of 850 (Oe) and a saturation magnetization of 57 (emu / emu /
g) and the specific surface area is 35 (m ² / G). The moisture content at this time is measured by a moisture measuring device (C
A-06 / VA-06), the result was 0.0110 (g) per 1 g of the magnetic powder as shown in Table 1. Using the magnetic powder for magnetic recording thus obtained,
The magnetic paint was prepared as follows. (Coating composition) Magnetic powder for magnetic recording 100 parts by weight Sulfonated vinyl chloride resin 10 parts by weight Dispersant (lecithin) 3 parts by weight Abrasive (Al ₂ O ₃ ) 2 parts by weight Lubricant (StA / StBu) 2 parts by weight Curing agent (coronate) 4 parts by weight Methyl ethyl ketone 40 parts by weight Toluene 40 parts by weight Cyclohexanone 40 parts by weight The above-mentioned various materials were kneaded for 5 hours with a sand grinder.

During kneading, the coating material was sampled every hour and coated on a 9-micron polyethylene terephthalate film using an applicator having a gap width of 30 microns to prepare a coating film. The gloss of this coating film was measured using a Nippon Denshoku gloss meter (entrance reflection angle: 60 degrees) to examine the degree of dispersion of the magnetic powder. Further, the paint after 5 hours of kneading was applied to a KBr plate, and an FT-IR device (FT / IR-) manufactured by JASCO Corporation was used.
7000) to examine the curing rate of the coating material by examining the time change of the absorption intensity ratio of the -CH group and the -NCO group.

Further, using a paint after 5 hours of kneading, a magnetic film of 3 microns was coated on a polyethylene terephthalate film of 9 microns, dried and calendered to form a magnetic layer, which was cut into 8 mm width. To form a magnetic tape. Then, the coercive force of the magnetic tape was measured using a vibrating sample magnetometer (VSMP-1) manufactured by Toei Industry Co., Ltd. in the same manner as the magnetic powder. Also, the output and S / N in the 5 MHz band of this magnetic tape were measured.

Table 2 shows the change of the glossiness thus obtained with respect to the dispersion time, the curing rate of the coating material, the coercive force ratio (magnetic layer coercive force / magnetic powder coercive force), output and S / N.
The curing speed of the paint is shown by the time when the value of (-NCO strength / -CH strength) becomes 1/2. (Specific example 2)

First, Co and Ti are formed by a glass crystallization method.
And Sn-substituted Ba ferrite magnetic powder were prepared. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. This magnetic powder for magnetic recording has a coercive force of 1180 (Oe), a saturation magnetization of 57 (emu / g) and a specific surface area of 40 (m ² ) as shown in Table 1. / G), and the water content was 0.0126 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Specific example 3)

Co, Zn and Nb substituted Ba ferrite magnetic powders were prepared by the glass crystallization method. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. This magnetic powder for magnetic recording is shown in Table 1.
As shown in, coercive force 1150 (Oe), saturation magnetization 61
(Emu / g), specific surface area 38 (m ² / G), and the water content was 0.0120 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Specific Example 4) The same Co, Zn and Nb-substituted Ba ferrite magnetic powder as in Specific Example 3 was prepared by the glass crystallization method.

Then, the magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder is heated to 25 ° C. and 50
It was placed in a large vessel kept at% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. This magnetic powder for magnetic recording has a coercive force of 1160 as shown in Table 1.
(Oe), saturation magnetization 61 (emu / g), specific surface area 38
(M ² / G), and the water content was 0.0078 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Specific Example 5)

Co, Zn, and Nb-substituted Ba ferrite magnetic powders were prepared by the glass crystallization method. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. This magnetic powder for magnetic recording is shown in Table 1.
, The coercive force is 1200 (Oe) and the saturation magnetization is 55.
5 (emu / g), specific surface area 60 (m ² / G) and the water content was 0.0189 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Specific Example 6)

By the glass crystallization method, Co, Zn, Nb
And Sn-substituted Ba ferrite magnetic powder were prepared. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. As shown in Table 1, the magnetic powder for magnetic recording has a coercive force of 1100 (Oe), a saturation magnetization of 59 (emu / g), and a specific surface area of 40 (m ^2). / G), and the water content was 0.0131 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Specific Example 7)

By the glass crystallization method, Co, Zn, Ni
And Ti-substituted Ba ferrite magnetic powder were prepared. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. As shown in Table 1, this magnetic powder for magnetic recording has a coercive force of 1145 (Oe), a saturation magnetization of 59.5 (emu / g), and a specific surface area of 41 (m ^2). / G)
The water content was 0.0122 (g). A magnetic tape was obtained in the same manner as in Example 1 using the magnetic powder for magnetic recording. (Comparative Example 1)

Co, Ti and Sn substituted Ba ferrite magnetic powders were prepared by the glass crystallization method. Then, this magnetic powder was put into water and sufficiently stirred while applying ultrasonic waves to obtain a water slurry. The slurry was dried with a spray dryer and collected in a container filled with dry nitrogen. Next, the dry powder was placed in a large vessel kept at 25 ° C. and 60% RH to adsorb moisture in the environment inside the vessel to obtain magnetic powder for magnetic recording. This magnetic powder for magnetic recording is shown in Table 1.
As shown in, the coercive force is 500 (Oe) and the saturation magnetization is 56 (e).
mu / g), specific surface area 35 (m ² / G), and the water content was 0.0107 (g). Using such magnetic powder for magnetic recording, a magnetic tape was obtained in the same manner as in Example 1. (Comparative example 2)

A magnetic tape was obtained in the same manner as in Example 1 except that the Co, Ti and Sn-substituted Ba ferrite magnetic powder shown in Example 2 was used without moisture adsorption. The magnetic powder for magnetic recording has a coercive force of 1190 as shown in Table 1.
(Oe), saturation magnetization 57.5 (emu / g), specific surface area 40 (m ^2). / G) and the water content was 0.0048 (g). (Comparative example 3)

A magnetic tape was obtained in the same manner as in Example 1 except that the Co, Zn and Nb-substituted Ba ferrite magnetic powder shown in Example 3 was used without moisture adsorption. The magnetic powder for magnetic recording has a coercive force of 1165 as shown in Table 1.
(Oe), saturation magnetization 61.5 (emu / g), specific surface area 38 (m ^2). / G), and the water content was 0.0045 (g). (Comparative example 4)

Except that the Co, Zn and Nb-substituted Ba ferrite magnetic powder shown in Example 3 was placed in a large vessel kept at 40 ° C. and 90% RH and the magnetic powder for magnetic recording adsorbed water was used. A magnetic tape trial production was attempted in the same manner as in Example 1, but the stability of the paint was poor and a tape of sufficient length was used.
I couldn't get it. The magnetic powder for magnetic recording is shown in Table 1.
, The coercive force is 1140 (Oe) and the saturation magnetization is 60.
5 (emu / g), specific surface area 38 (m ² / G), and the water content was 0.0178 (g).

[0034]

[Table 1]

[0035]

[Table 2]

From the specific examples and comparative examples described above, in Comparative Examples 2 and 3 in which the water content is small, the rise of dispersion is slow,
It can be seen that the gloss after 5 hours did not increase, the coercive force change rate was small, and the degree of dispersion was low. On the contrary, in Comparative Example 4 in which the water content is large, although the dispersion proceeds to some extent, the curing rate is high and the stability of the coating is poor.

On the other hand, according to this example, since the water content and the coercive force are within the predetermined ranges,
From the measurement results of the coercive force ratio, gloss, output, S / N, etc., it can be understood that the dispersibility is extremely excellent.

The samples used in the examples were prepared by drying in a spray dryer and collecting in a container filled with nitrogen, and then adjusting the water content. At this time, the magnetic powder only needs to satisfy the range of the present invention.

[0039]

As described above, the magnetic powder for magnetic recording of the present invention has very excellent dispersibility, so that it can be made into a paint much more easily than in the past. Further, a magnetic recording medium made of such magnetic powder for magnetic recording is also excellent in output and S / N characteristics, and is very effective in increasing the density.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuji Ogawa 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (2)

[Claims] 1. The specific surface area measured by the BET method using nitrogen gas is SBET (m ² / G), 1.35 × 10 ⁻⁴ × SBET (g) or more per unit mass, 4.3 ×
Magnetic powder for magnetic recording, which contains water of 10 ⁻⁴ × SBET (g) or less and has a coercive force of more than 800 (Oe). 2. The specific surface area measured by the BET method using nitrogen gas is SBET (m ² / G), 1.35 × 10 ⁻⁴ × SBET (g) or more per unit mass, 4.3 ×
A magnetic recording medium comprising a magnetic layer comprising magnetic powder having a water content of 10 ⁻⁴ × SBET (g) or less and a coercive force of more than 800 (Oe) dispersed in a resin.