JPH09180170A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium for high density recording generating low noise and excellent in orienting property by dispersing hexagonal ferromagnetic powder having a specified specific surface area and a specified coercive force in a resin binder. SOLUTION: This magnetic recording medium contains hexagonal ferromagnetic powder having 25-45m<2> /g specified surface area and 400-2,000Oe coercive force dispersed in 10-40 pts.wt. resin binder based on 100 pts.wt. of the powder. In the case of <400Oe coercive force, it is difficult to increase recording density. In the case of >2,000Oe, a magnetic recording head is liable to cause saturation. The ferromagnetic powder is preferably Baferrite powder and the axes of easy magnetization of the powder have been preferably oriented in a direction perpendicular to the surface of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium for high density recording which has low noise and excellent orientation.

[0002]

2. Description of the Related Art Most of conventional magnetic recording media are constructed by coating a magnetic coating material comprising magnetic powder and a resin binder on a supporting substrate such as a polyester film. The magnetic The powder gamma-Fe ₂ O ₃ system, Fe ₃ O ₄ system and these cobalt adsorption system, or CrO acicular ferromagnetic powder used ₂ system or the like is mainly used. However, these needle-shaped ferromagnetic powders have a drawback that they cannot meet the recent demands for high-density recording because their coercive force is small and the recording density has already reached its limit. Therefore, it has recently been considered to reduce the particle length of the acicular ferromagnetic powder as much as possible or to improve the coercive force (Hc) and the maximum magnetic flux density (Ms) in order to improve this defect. However, if the particle length is reduced in these acicular ferromagnetic powders,
Due to the influence of the demagnetizing field, the electromagnetic conversion characteristics in the low frequency range deteriorated, and there was a drawback that sufficient improvement in characteristics could not be expected.

On the other hand, a so-called metal tape is known in which fine powder of magnetic iron powder is dispersed in a resin binder and the obtained magnetic coating is applied to the surface of a supporting substrate. This has the advantage of enabling higher density magnetic recording than in the case of conventional γ-Fe ₂ O ₃ magnetic iron oxide, but on the other hand, it is easily oxidized by oxygen in the air, and There is an extremely high risk of explosion in the manufacturing process of the magnetic coating material, and it is difficult to handle the magnetic coating material, and the long-term stability of the characteristics of the magnetic recording medium is poor.

Hexagonal system ferromagnetic powder, which is chemically stable and is suitable for perpendicular magnetic recording, has been attracting attention as a magnetic powder capable of solving such problems and enabling high density recording. This is because the perpendicular magnetic recording method is essentially suitable for high-density recording because the demagnetizing field in the recording medium decreases as the recording density increases.

The hexagonal ferromagnetic powder is usually a hexagonal plate-like particle and has an easy axis of magnetization in the direction perpendicular to the plate surface. For this reason, even if this magnetic powder is applied, the plate surface is likely to be parallel to the supporting substrate surface, and the easy axis of magnetization is easily vertically aligned by the magnetic field orientation treatment or the mechanical orientation treatment.
Therefore, a hexagonal ferromagnetic powder having such properties is used as a fine powder having a single domain structure (average particle size of 0.25 μm or less).
As a result, if it is applied uniformly on the surface of the supporting substrate together with the resin binder, it is expected that the magnetic recording medium will have an extremely high recording density.

However, when the hexagonal ferromagnetic powder becomes a fine powder having an average particle size of 0.25 μm or less, the cohesive force between particles becomes large, so that it can be highly dispersed in the magnetic paint. It will be extremely difficult. as a result,
The perpendicular orientation of the obtained magnetic recording medium is deteriorated, and the reproduction output characteristics in the high range are not as excellent as initially expected, and the noise characteristics are low.

When the average particle size of the magnetic powder is 0.2 μm or more, the dispersibility is slightly improved, but the above-mentioned circumstances also apply to this case. Therefore, it has been desired to improve the dispersibility of the hexagonal ferromagnetic powder and thereby enhance the orientation and noise characteristics of the magnetic recording medium using the same.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium for high density recording which has low noise and excellent orientation.

[0009]

As a result of intensive studies to achieve the above object, the present inventors have found that hexagonal ferromagnetic powder has an average particle size of 0.05 to 0.25 μm. There is not necessarily an inverse proportional relationship between the particle size and the size of the specific surface area, and the quality of the dispersibility does not directly depend on the particle size, but it was found that there is a strong correlation with the size of the specific surface area. Completed the invention.

That is, in the magnetic recording medium of the present invention, a hexagonal ferromagnetic powder having a specific surface area of 23 to 45 m ² / g and a coercive force of 400 to 2000 Oe is 1 to 100 parts by weight of the powder.
It is characterized by being dispersed in 0 to 40 parts by weight of a resin binder.

The hexagonal ferromagnetic powder used is Co,
Fine particles of a metal such as Co-Cr, Co-Mn, and Mn-Al that form hexagonal crystals by themselves, a general formula MO · n (F
e ₂ O ₃ ) hexagonal ferrite (M is B
Any one of a, Sr, Pb, and Ca, n is 5 to 6, and part of Fe is Ti, Co, Zn, In, Mn, and C.
It may be substituted with a transition metal such as u, Ge or Nb)
And the like, and preferably hexagonal ferrite, more preferably Ba-ferrite.

Since hexagonal ferrite generally has a high coercive force, some of the constituent atoms have been replaced with specific atoms and the coercive force thereof has been reduced to a range suitable for perpendicular magnetic recording.
It is preferable as the magnetic powder of the present invention.

The coercive force of the magnetic powder is 400 to 2000 O
Let be e. If the coercive force is less than 400 Oe, it is difficult to increase the recording density, and if it exceeds 2000 Oe, the magnetic recording head tends to be saturated, which is inconvenient.

The specific surface area of the hexagonal ferromagnetic powder is 23-4.
And 5m ² / g, preferably with 25~40m ² / g. Here, the specific surface area means the surface area of the powder per unit weight measured by the BET adsorption method of nitrogen gas. The specific surface area is set to 23 to 45 m ² / g because the adsorption force of the binder such as resin to the magnetic powder surface overcomes the cohesive force between the magnetic powder particles in this region, and the magnetic powder is evenly distributed in the magnetic paint or coating film. Is not only dispersed, but also improves the fluidity of the paint, resulting in a smooth coating surface. As a result, the orientation of the magnetic recording medium is enhanced, and the reproduction output characteristic and noise characteristic are improved. In other words, when the specific surface area is less than 23 m ² / g, the adsorption of the binder becomes insufficient, the cohesive force of the magnetic powder overcomes the adsorption force of the binder, and the specific surface area is 45 m ² / g.
When it exceeds, the cohesive force of the magnetic powder increases due to the increase in the surface energy of the magnetic powder, and since the cohesive force of the magnetic powder overcomes the adsorption force of the binder, the dispersibility of the magnetic powder decreases. Playback output characteristics and noise characteristics are degraded.

The particle size of the hexagonal ferromagnetic powder is 0.0
It is 5 to 0.25 μm, preferably 0.05 to 0.2 μm. If the average particle size is less than 0.05 μm, the thickness of the non-magnetic layer on the surface of the magnetic powder cannot be ignored, the maximum magnetic flux density (Ms) of the magnetic powder begins to decrease, and the orientation also decreases, resulting in high density. It becomes difficult to record. On the other hand, when the average particle size exceeds 0.25 μm, the orientation is improved, but the magnetic cohesive force of the magnetic powder increases, so that noise increases, making high-density recording difficult as in the above case.

Such hexagonal ferromagnetic powders are disclosed in Japanese Patent Application No. 54-143859 and Japanese Patent Application No. 55-55, filed by the present applicant.
It can be produced by the glass crystallization method described in the specification of No. 34769. In adjusting the specific surface area and particle size of these magnetic powders, a wide range of specific surface area and particle size can be obtained by appropriately changing the reaction conditions during production.

As the resin binder to be used, any film-forming material having flexibility, which is compatible with the support material and the magnetic powder, can be used. Examples of these are vinyl chloride-vinyl acetate-based copolymer materials, NBR-polyvinyl acetate-based materials, urethane plasticized vinyl chloride-vinyl acetate-based copolymer materials, polyurethane-based materials, polyester-based resins, isocyanate-based materials. Known materials such as The magnetic recording medium of the present invention is usually coated on a supporting substrate excellent in mechanical properties such as flexibility, tensile strength and dimensional stability, for example, a polyester film. By coating the magnetic recording medium on the supporting substrate in this manner, handling of the magnetic recording medium becomes extremely easy.

The magnetic recording medium of the present invention can be obtained, for example, as follows. That is, first, in a dispersing / mixing machine such as a sand grinder pot, the hexagonal ferromagnetic powder and the resin binder, and a predetermined amount of a solvent are appropriately added, and then the mixing machine is operated to operate the magnetic paint. To prepare.

At this time, the compounding ratio of the magnetic powder and the resin binder is such that the resin binder is 10 to 100 parts by weight of the magnetic powder.
40 parts by weight. If the resin binder is less than 10 parts by weight,
The uniformity and stability of the magnetic paint are impaired. As a result, the smoothness of the medium surface deteriorates, the space loss between the head and the medium increases, and the output decreases. On the other hand, the resin binder is 4
If it exceeds 0 parts by weight, the filling amount of the magnetic powder becomes insufficient, and therefore the maximum magnetic flux density (Ms) of the medium becomes small, so that the output also decreases. Magnetic paint is also used as antistatic conductive material such as carbon black, dispersant such as lecithin,
Known additives such as lubricants, abrasives and stabilizers can be added.

Next, the obtained magnetic coating material is applied by a known method using, for example, a reverse roll coater, a doctor blade coater, a gravure coater, or the like, and preferably magnetic field orientation is carried out in a direction perpendicular to the surface of the supporting substrate. The magnetic recording medium of the present invention is obtained by performing a drying / smoothing process while performing the treatment or the mechanical orientation treatment. At that time, the orientation of the magnetic powder is, for example, Japanese Patent Application No. 54-7 filed by the present applicant.
1278, Japanese Patent Application No. 55-132145, Japanese Patent Application No. 55
-132138 can be performed by the method and apparatus described in it.

[0021]

As is apparent from the above description, since the magnetic recording medium of the present invention uses hexagonal ferromagnetic powder, the easy axis of magnetization of the magnetic layer is easily oriented vertically and its specific surface area is 23 to 45 m. ^Since it is ² / g, the dispersibility is good, and as a result, the smoothness of the coating film, the orientation rate, and the noise characteristics are excellent. Therefore, it has the effect of enabling high-density recording. The value is extremely large.

[0022]

EXAMPLES The magnetic recording medium of the present invention will be described in detail below with reference to examples.

Example 1 As a hexagonal ferrite powder, the average particle size was 0.09 μm.
, Specific surface area 27 m ² / g, coercive force 780 Oe, maximum magnetic flux density 59 emu / g substitutional barium ferrite BaO ・ 6
To 100 parts by weight of {(Fe _0.86 Co _0.07 Ti _0.07 ) ₂ O ₃ } powder, 8.3 parts by weight of conductive carbon black, 6.7 parts by weight of lecithin, 100 parts by weight of methyl ethyl ketone, and 66.7 parts by weight of toluene were added. After mixing well, a vinyl chloride-vinyl acetate copolymer (trademark VAGH:
Union Carbide Co., Ltd.) 10 parts by weight and polyurethane resin (Trademark N-2301: Nippon Polyurethane Co., Ltd.)
(Manufactured by Mfg. Co., Ltd.) was added and mixed, and the mixture was dispersed in a sand grinder pot for about 2 hours. The magnetic paint obtained was filtered and the polyisocyanate curing agent (trademark Coronate L:
After adding Nippon Polyurethane Co., Ltd., apply it on a polyester film with a reverse roll coater,
Drying while passing through a vertical magnetic field, coating thickness about 2μm
The magnetic layer of Finally, this was passed through a super calender roll device and smoothed to obtain a magnetic recording medium of the present invention.

For this magnetic recording medium, the surface roughness of the magnetic layer, the vertical orientation ratio and the carrier signal-to-noise ratio (C /
N) (4MHz carrier, tape speed 3.5m / sec)
Was measured. The results are shown in the following table. The values of carrier signal to noise ratio (C / N) in Table 1 are 0.27 μm as magnetic powder, specific surface area 36 m ² / g, coercive force 12
This is a relative value based on the C / N value (0 dB) of a metal tape obtained by a method similar to the above, using a ferromagnetic metal powder having a magnetic flux density of 70 Oe and a maximum magnetic flux density of 170 emu / g. First
As is clear from the table, the magnetic recording medium of the present invention had a smooth coating film surface, a high vertical orientation rate and an excellent C / N value.

Example 2 Instead of the hexagonal ferrite used in Example 1, an average particle size of 0.17 μm, a specific surface area of 35 m ² / g, a coercive force of 740 Oe,
Substitution type barium ferrite B with maximum magnetic flux density of 60emu / g
A magnetic recording medium of the present invention was obtained in the same manner as in Example 1 except that aO.6 {(Fe _0.86 Co _0.07 Ti _0.07 ) ₂ O ₃ } powder was used, and the surface roughness and vertical orientation of the magnetic layer were obtained. The rate and C / N value were measured. The results are shown in the following table. As is apparent from Table 1, the magnetic recording medium of the present invention had a smooth coating film surface, a high vertical orientation rate and an excellent C / N value.

Example 3 Instead of the hexagonal ferrite used in Example 1, an average particle size of 0.25 μm, a specific surface area of 33 m ² / g and a coercive force of 830O
e, by the same method as in Example 1 except that the substitution type barium ferrite BaO · 6 {(Fe _0.86 Co _0.07 Ti _0.07 ) ₂ O ₃ } powder having a maximum magnetic flux density of 61 emu / g was used.
The magnetic recording medium of the present invention was obtained, and the surface roughness of the magnetic layer, the vertical orientation rate and the C / N value were measured. The results are shown in the following table. As is clear from Table 1, the magnetic recording medium of the present invention has a smooth coating surface, a relatively high vertical orientation rate, and an excellent C /
It had an N value.

Comparative Example 1 Average particle size 0.08 having almost the same chemical composition as in Example 1.
A magnetic recording medium was obtained in the same manner as in Example 1 except that the substitutional barium ferrite powder having a μm, a specific surface area of 19 m ² / g, a coercive force of 810 Oe and a maximum magnetic flux density of 60 emu / g was used. Surface roughness, vertical orientation ratio and C /
The N value was measured. The results are shown in Table 1. As is clear from comparison of this result with the result of the example, the characteristics of the smoothness of the coated surface, the vertical orientation ratio, and the C / N value were all inferior to those of the magnetic recording medium of the present invention.

Comparative Example 2 Average particle size 0.24 having almost the same chemical composition as in Example 1.
A magnetic recording medium was obtained in the same manner as in Example 1 except that a substitutional barium ferrite powder having a μm, a specific surface area of 22 m ² / g, a coercive force of 780 Oe, and a maximum magnetic flux density of 61 emu / g was used. The surface roughness and C / N value were measured.
The results are shown in Table 1. As is clear by comparing this result with the result of the example, the smoothness of the coated surface,
Both characteristics of C / N value were inferior to the magnetic recording medium of the present invention.

Comparative Example 3 Average particle size 0.06 having substantially the same chemical composition as in Example 1.
A magnetic recording medium was obtained by the same method as in Example 1 except that a substitutional barium ferrite powder having a μm, a specific surface area of 51 m ² / g, a coercive force of 760 Oe, and a maximum magnetic flux density of 52 emu / g was used. Surface roughness, vertical orientation ratio and C /
The N value was measured. The results are shown in Table 1. As is clear from comparison of this result with the result of the example, all the characteristics of the smoothness of the coated surface, the vertical orientation ratio, and the C / N value were inferior to those of the magnetic recording medium of the present invention.

[0030]

[Table 1]

TEST EXAMPLE Average particle size 0.06 having approximately the same chemical composition as in Example 1.
～0.1Myuemu, the various substituted barium ferrite powder having a specific surface area of 14~45m ² / g, by the same method as in Example to obtain a magnetic recording medium. The carrier signal-to-noise ratio C / N value (4 MHz carrier, tape speed 3.5 m / sec) of these was measured, and the relationship between the value and the specific surface area of the magnetic powder was determined. The result is shown in the figure. As is clear from FIG. 1, the magnetic powder having a specific surface area of 23 to 45 m ² / g showed an excellent C / N value. Incidentally, the C / N value on the vertical axis in FIG. 1 represents a relative value based on the C / N value (0 dB) of the same metal tape as described above.

[Specificity of Numerical Limit Range] Examples 1 to 3,
Comparative Examples 1 to 3 are 100 parts by weight of magnetic powder and VA vinyl chloride.
This is an example of 10 parts by weight of GH and 10 parts by weight of urethane N-2301 with 20 parts by weight of the total resin binder. Tests were also carried out to demonstrate that the properties of the present invention within the numerical limits were unique. The test was carried out according to the solvent composition and other additive compositions as in the example.
The compounding ratio of GH and urethane N-2301 was set to 1: 1 as in the example, and the lower limit and the upper limit of 10 to 40 parts by weight of the resin binder with respect to 100 parts by weight of the magnetic powder and the outside thereof and the specific surface area of the magnetic powder of 23 to 45 m ^{2 were used.} The lower limit and the upper limit of / g and the outside thereof were performed. As the magnetic powder, the powder used in Comparative Example 2 and Test Example was used. Table 2 shows the test contents.

[0033]

[Table 2]

The test results are shown in Table 3.

[0035]

[Table 3]

Symbols E4 to E7 in Tables 2 and 3
Shows good experimental data within the range of Examples 1 to 3, and C4 to C11 show inferior comparative data presented following Comparative Examples 1 to 3.

The results of Table 3 are shown in the graph of FIG. As is clear from FIG. 2, E4 and E5 have a specific surface area of 23 m ² / g, which is the lower limit, and a resin binder, which is the lower limit and the upper limit, of D to 0.1.
Although it has a slightly rough surface, reflecting that it is 2 μm,
The C / N value is equal to or higher than that of metal tape.

E6 and E7 have a specific surface area of 43 m ² /
g, the resin binder is the lower limit and the upper limit, D ~ 0.02
The surface property is good reflecting the fact that it is μm. However, although the Ms and SQR tend to decrease due to a decrease in orientation, a decrease in σ, and difficulty in filling fine particles, the C / N value is secured to be equal to or higher than that of the metal tape.

C4 and C5 have a specific surface area of 22 below the lower limit.
m ² / g, the lower limit and the upper limit of the resin binder, D ~ 0.2
Reflecting the fact that it is 4 μm, the surface property is rough in all resin amount regions, the particle noise is dominant, and the C / N value is much lower than 0 dB compared to the metal tape.

C6 and C7 are media prepared by changing the resin amount of the E4 and E5 powders. When the resin amount of 9 parts is combined with the powder having a specific surface area of 23 m ² / g which is the lower limit, the surface energy of the magnetic powder cannot be reduced by this amount of resin and the dispersibility of the magnetic powder is reduced, resulting in a rough surface property. Become. The resin amount of 41 parts is excessive and a structure due to the interaction between the resins appears, so that the surface property is deteriorated and the orientation is also hindered. Further, the C / N value is out of the problem because the output is low and the noise is high due to the poor filling property.

C8 and C9 are media prepared by changing the amount of resin from the powders of E6 and E7. Specific surface area is 43m ² / g and resin 9
With the combination of the parts, the surface energy of the magnetic powder cannot be lowered by this amount of resin, and the dispersibility of the magnetic powder is lowered, so that the surface property is further lowered as compared with E6. In combination with 41 parts, the surface energy of the magnetic powder can be lowered and the surface property is improved, but the orientation is lowered, σ is lowered, Ms is lowered in combination with the difficulty of filling a large amount of resin and fine particles, Further, due to the decrease in SQR, the output component is small and the noise component is small, but the C / N value cannot be earned.

C10 and C11 are impossible for the same reason as C8 and C9. As shown by the above experimental data, the magnetic recording medium of the present invention exhibits more specific characteristics within the limited range of the specific surface area and the resin binder than those outside the range.

[Brief description of the drawings]

FIG. 1 shows the relationship between the specific surface area of magnetic powder and the C / N value of a magnetic recording medium when 100 parts by weight of hexagonal ferromagnetic powder are dispersed in 20 parts by weight of a resin binder. It is explanatory drawing of this invention shown.

FIG. 2 shows the same material as shown in FIG. 1 with specific surface areas set at the lower limit, the upper limit, below the lower limit and above the upper limit of the present invention, and It is a figure which shows in a graph the data of the experimental example and comparative example which set and measured the amount of the lower limit, the upper limit, below the lower limit, and above the upper limit of the limiting range of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsumi Maeda 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Higashi Koshibaura Electric Co., Ltd.

Claims (3)

[Claims] 1. A specific surface area of 25 to 45 m ² / g and a coercive force of 4
A magnetic recording medium, characterized in that a hexagonal ferromagnetic powder of 0 to 2000 Oe is dispersed in 10 to 40 parts by weight of a resin binder with respect to 100 parts by weight of the powder. 2. The magnetic recording medium according to claim 1, wherein the hexagonal ferromagnetic powder is Ba-ferrite. 3. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is coated on a supporting substrate, and the easy axis of magnetization of the magnetic powder is oriented in a direction perpendicular to the surface of the supporting substrate. recoding media.