JPH08106622A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE: To improve durability by specifying the ratio of the residual magnetic flux density in a longitudinal direction measured when a magnetic field is removed after the magnetic layer surface of a magnetic recording medium provided with a magnetic layer contg. platelike hexagonal ferrite powder on a nonmagnetic substrate is subjected to saturation magnetization in a perpendicular direction and the saturation magnetic flux density in the longitudinal direction to a prescribed value. CONSTITUTION: The axis of easy magnetization of the planar hexagonal ferrite powder in the magnetic coating film 2 is oriented in the longitudinal direction like an arrow A on a base film 3 formed with the magnetic coating film 2 of a fluid state coated with a magnetic coating material between opposed N-N magnets 1a, 1b at the left end of Fig. Next, the axis of easy magnetization of the platelike hexagonal ferrite powder is oriented in a C direction from a B direction by the opposed S-N magnets 4a, 4b on the right side, then the opposed S-N magnets 5a, 5b. The ratio of the residual magnetic flux density Br' in the longitudinal direction and the saturation magnetic flux density Bs in the longitudinal direction measured when the magnetic field is removed after the magnetic layer surface is subjected to saturation magnetization in the direction perpendicular thereto is specified to a relation satisfying 0.2<Br'/Bs<0.6.

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 using a plate-shaped hexagonal ferrite powder as a recording element and a method for producing the same, and more specifically to the above magnetic recording medium excellent in electromagnetic conversion characteristics and durability. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is prepared by coating and drying a magnetic coating material prepared by mixing and dispersing magnetic powder with a binder resin, an organic solvent and other necessary components on a substrate. The demand for higher recording density for this type of magnetic recording medium is increasing. For this reason,
As a magnetic powder, it has been practiced to use a plate-shaped hexagonal ferrite powder, and in particular, an easy axis of magnetization that is perpendicular to the plate surface of the plate-shaped hexagonal ferrite powder is oriented in the longitudinal direction of the magnetic layer. And the coercive force squareness ratio of the magnetic recording medium becomes about 0.9 or more due to the interparticle interaction that occurs when the powder particles come into contact with the plate surface and stacking occurs, and the magnetic recording medium using the conventional acicular magnetic powder It has a higher coercive force squareness ratio of about 0.7 and exhibits excellent short wavelength characteristics.Therefore, it is possible to orient this kind of plate-shaped hexagonal ferrite powder in the longitudinal direction of the magnetic layer to achieve high recording density. Being tried.

[0003]

However, when this type of plate-shaped hexagonal ferrite powder is exposed to a strong orienting magnetic field in order to orient it in the longitudinal direction, the squareness becomes higher, but the stacking degree of the powder particles is increased. There is a drawback that it becomes too large and causes an increase in noise. In addition, when the calendering treatment, which is indispensable in order to improve the surface smoothness of the magnetic layer and to improve the short wavelength characteristics, is performed, the plate-like hexagonal ferrite powder is erected on the magnetic layer surface by the longitudinal orientation. Occurs, and the orientation is disturbed, and the short-wavelength characteristics are rather deteriorated. In extreme cases, the surface of the magnetic layer is cracked and durability is significantly reduced.

[0004]

The present invention has been made as a result of various studies in view of such circumstances. After applying a magnetic coating material containing plate-shaped hexagonal ferrite powder on a non-magnetic substrate, the The easy axis is oriented in the longitudinal direction, then the easy axis is oriented in the vertical direction, and the magnetic layer is oriented by applying a magnetic field having an average direction of 10 to 60 ° in the direction perpendicular to the magnetic layer surface. The ratio Br ′ / Bs of the residual magnetic flux density Br ′ in the longitudinal direction and the saturated magnetic flux density Bs in the longitudinal direction measured when the magnetic field is removed after saturation magnetization in the direction perpendicular to the magnetic layer surface is 0.2 <Br ′ / By satisfying the relationship of satisfying Bs <0.6, stacking of the plate-shaped hexagonal ferrite powder is made moderate, and the plate-shaped hexagonal ferrite powder is not disturbed by the calendar treatment. It is oriented well and the electromagnetic conversion characteristics and durability are sufficiently improved.

In the present invention, the magnetic field orientation of the plate-shaped hexagonal ferrite powder is first determined between the N-N facing magnets 1a and 1b at the left end as shown in the magnetic field orientation process explanatory diagram of the plate-shaped hexagonal ferrite powder of FIG. The magnetic film is applied to the base film 3 on which the magnetic coating film 2 in a fluidized state is formed, and the easy axis of magnetization of the plate-like hexagonal ferrite powder in the magnetic coating film 2 is indicated by an arrow. As shown in A, it is oriented in the longitudinal direction.

Then, it is introduced between the S-N facing magnets 4a and 4b in the central portion, and this time, the easy axis of magnetization of the plate-shaped hexagonal ferrite powder in the magnetic coating film 2 is indicated by an arrow B. The SN facing magnet 5 is composed of a magnet 5a which is oriented in the vertical direction and is further widened, and a magnet 5b whose width at the right end is narrowed and magnet 5b whose width is narrowed so that the entrance side end face is aligned with the magnet 5a.
It is introduced between a and 5b, and is oriented by applying a magnetic field having a direction of magnetic force lines in the direction of 10 to 60 ° on average in the direction perpendicular to the surface of the magnetic coating film 2.

However, the plate-like hexagonal ferrite powder in the magnetic coating film 2 in the fluidized state is first of all the N-N facing magnet 1 at the left end.
The axes of easy magnetization are aligned in the longitudinal direction by a and 1b as shown by the arrow A, and then the SN facing magnet 4 in the central portion is aligned.
By applying a magnetic field in the vertical direction by a and 4b, the particles are oriented in the vertical direction as shown by arrow B, so that the powder particles easily flow so that their plate surfaces are parallel to each other.
Further, the SN facing magnets 5a and 5b at the right end further apply a magnetic field having a magnetic force line component in an oblique direction while gradually changing the angle with respect to the magnetic layer surface, so that the plate-shaped hexagonal ferrite powder is The planes are aligned in an oblique direction with respect to the magnetic layer plane, and the easy axis of magnetization is finally oriented as shown by an arrow C.

Therefore, the stacking degree of the hexagonal ferrite powder particles does not become too large, which causes an increase in noise, and even if the calendering is continuously performed, the plate surfaces of the hexagonal ferrite powder particles are uniform. Therefore, the disorder of the orientation of the hexagonal ferrite powder particles is also suppressed. As a result, the plate-like hexagonal ferrite powder is favorably oriented, the surface smoothness of the magnetic layer surface is improved, the electromagnetic conversion characteristics are sufficiently improved, and the magnetic layer surface is not cracked. Durability is sufficiently improved.

Thus, when the easy axis of magnetization of the plate-like hexagonal ferrite powder is finally oriented obliquely with respect to the magnetic layer surface as shown by arrow C in FIG.
The magnetic field applied by the opposing magnets 5a and 5b is a magnetic field having a direction of magnetic force lines in the direction of 10 to 60 ° on average in the direction perpendicular to the magnetic coating film 2 surface, and saturated magnetization is applied in the direction perpendicular to the magnetic layer surface. After that, the ratio Br ′ / Bs of the residual magnetic flux density Br ′ in the longitudinal direction and the saturation magnetization density Bs in the longitudinal direction measured when the magnetic field is removed is set to satisfy the relationship of 0.2 <Br ′ / Bs <0.6. Is preferred, and this Br
If ´ / Bs is less than 0.2, the output will decrease, and
When it is larger than 6, noise tends to increase, which is not preferable.

Further, the plate-like hexagonal ferrite powder used in the present invention is a plate-like hexagonal ferrite powder containing various substitution elements produced by a conventional manufacturing method such as a hydrothermal method or a flux method in glass. Is preferable, and if the coercive force is less than 200 Oersted, high-density recording cannot be performed, and if it exceeds 2000 Oersted, the current magnetic head cannot perform sufficient magnetic recording.
Those having a coercive force of 200 to 2000 Oersted are preferably used. The average particle size is 0.02.
If it is less than μm, sufficient magnetic properties cannot be obtained, and if it exceeds 0.5 μm, the surface smoothness of the magnetic layer cannot be sufficiently improved and high density recording cannot be performed, so 0.02 μm to 0.5 μm
Those within the range are preferably used.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, a plate-shaped hexagonal ferrite powder is mixed and dispersed with a binder resin, an organic solvent and the like to prepare a magnetic coating material. After coating this magnetic coating on a non-magnetic substrate such as a polyester film by any coating means such as a roll coater, first the easy axis of magnetization is oriented in the longitudinal direction, and then the easy axis of magnetization is oriented in the vertical direction. Let
Furthermore, it is 10 to 60 ° on average in the direction perpendicular to the magnetic layer surface.
The residual magnetic flux density B in the longitudinal direction measured when the magnetic field is removed by applying a magnetic field having a direction of magnetic force lines to
The ratio Br ′ / Bs of r ′ and the saturation magnetic flux density Bs in the longitudinal direction
Should satisfy the relation of 0.2 <Br ′ / Bs <0.6.

The binder resin used here is a vinyl chloride-vinyl acetate copolymer, a polyvinyl butyral resin, a fibrin resin, a polyurethane resin, a polyester resin, an isocyanate compound, radiation curing. Conventionally widely used binder resins such as mold resins are widely used.

As the organic solvent, conventionally used organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, ethyl acetate and toluene may be used alone or in combination of two or more.

In the magnetic coating composition, various kinds of additives usually used, such as a dispersant, a lubricant, an abrasive and an antistatic agent, may be optionally added and used.

[0015]

EXAMPLES Next, examples of the present invention will be described. Example 1 1000 parts by weight of Co-Ti substituted barium ferrite hexagonal magnetic powder (average particle diameter 0.05 μm, average plate ratio 3, coercive force 1250 Oersted, saturation magnetization 58 emu / g) vinyl chloride-vinyl acetate-vinyl alcohol- Copolymer 137.5〃 (UCC; VAGH) Polyurethane resin (Dainippon Ink and Chemicals; Pandex 87.5 〃 T5201) α-Fe ₂ O ₃ powder 100 〃 Methyl isobutyl ketone 800 〃 Toluene 800 〃 After mixing and dispersing the product in a ball mill for 3 days,
80 parts by weight of oleyl oleate and a trifunctional isocyanate compound (Nippon Polyurethane Industry Co., Ltd .; Coroneate L) 2
5 parts by weight was added, and the mixture was further mixed and dispersed for 2 hours to prepare a magnetic coating material.

Then, the magnetic coating is applied to a gravure coater.
Is applied to a polyester film having a thickness of 14 μm, and then while the magnetic paint is in a flowing state, first, an easy axis of magnetization is set in the longitudinal direction by using a repulsive opposed magnet that generates a maximum magnetic field strength of 4 K oersted. Orientation is further performed, and the easy axis of magnetization is oriented in the vertical direction by using an attracting opposed magnet that generates a maximum magnetic field strength of 4K oersted, and then the direction of the magnetic field lines is in the direction of 20 ° on average in the direction perpendicular to the magnetic layer surface. It was oriented by passing through a magnetic field. After the orientation, the magnetic layer was dried to form a magnetic layer having a thickness of 2.5 μm, calendered and cut into a predetermined width to produce a magnetic tape.

Example 2 In the magnetic field orientation step in Example 1, after the easy axis of magnetization is oriented in the vertical direction, the subsequent orientation is averaged in the direction perpendicular to the surface of the magnetic layer and the direction of the magnetic field lines is 20 °. Magnetic field orientation was performed in the same manner as in Example 1 except that instead of a certain magnetic field, the magnetic field was oriented in the direction perpendicular to the surface of the magnetic layer and the direction of the magnetic force lines was 40 ° on average.
A magnetic tape was produced.

Comparative Example 1 In the magnetic field orientation step of Example 1, the application of the longitudinal orientation magnetic field and the vertical orientation magnetic field was omitted, and only the magnetic field in which the direction of the magnetic field lines was 20 ° on average in the direction perpendicular to the magnetic layer surface. A magnetic tape was produced in the same manner as in Example 1 except that the magnetic field was applied.

Comparative Example 2 In the magnetic field orientation step in Example 1, only the vertical orientation magnetic field was applied, and the longitudinal orientation magnetic field and the magnetic field in which the direction of the magnetic force line was 20 ° on average in the direction perpendicular to the magnetic layer surface. A magnetic tape was produced by orienting the magnetic field in the same manner as in Example 1 except that the application was omitted.

COMPARATIVE EXAMPLE 3 In the magnetic field orientation step in Example 1, only the longitudinal orientation magnetic field was applied, and the vertical orientation magnetic field and the magnetic field having the direction of the magnetic force line in the direction perpendicular to the magnetic layer surface were 20 °. A magnetic tape was produced by orienting the magnetic field in the same manner as in Example 1 except that the application was omitted.

The magnetic tape obtained in each Example and Comparative Example
The coercive force Hc in the longitudinal direction and the square Br / Bs,
The ratio Br ′ / of the residual magnetic flux density Br ′ in the longitudinal direction and the saturated magnetic flux density Bs in the longitudinal direction measured when the magnetic field is removed after the magnetic field is removed by applying a magnetic field of 10 K oersted in the direction perpendicular to the magnetic layer surface to cause saturation magnetization. Bs, maximum residual magnetic flux density B
m was measured to measure the surface roughness and still durability of the magnetic layer. Also, using an amorphous head with a gap length of 0.2 μm, the relative speed was 3.8 m / sec and the recording wavelength was 0.5 μm.
The output C is measured at the optimum recording current value at m,
Furthermore, C / N was measured. Regarding the surface roughness of the magnetic layer, the center line average roughness Ra was measured at a cutoff of 0.08 mm using a stylus type surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. The still durability was measured as the time required for the output to drop 6 dB from the initial output. Table 1 below shows the results.

[0022]

[0023]

As is apparent from Table 1 above, Example 1
The magnetic tapes of the present invention obtained in Nos. 1 and 2 are square Br / Bs, Br '/ Bs, outputs C and C /, respectively, as compared with the magnetic tapes obtained in Comparative Examples 1 to 3. The N content is high, the surface roughness of the magnetic layer is small, and the still durability is good. From this, the magnetic recording medium obtained by the present invention is
It can be seen that the electromagnetic conversion characteristics and durability are excellent.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a magnetic field orientation step of plate-like hexagonal ferrite powder in the present invention.

[Explanation of reference numerals] 1a, 1b NN counter magnet 2 magnetic coating film 3 base film (non-magnetic substrate) 4a, 4b SN counter magnet 5a, 5b SN counter magnet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaetsu Yoshida 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic layer containing plate-shaped hexagonal ferrite powder on a non-magnetic substrate, and a longitudinal direction measured when the magnetic field is removed after saturation magnetization in a direction perpendicular to the magnetic layer surface. Of the residual magnetic flux density Br 'and the saturation magnetic flux density Bs in the longitudinal direction, Br' / Bs, satisfy the relationship of 0.2 <Br '/ Bs <0.6. 2. A magnetic coating material containing a plate-shaped hexagonal ferrite powder is applied onto a non-magnetic substrate, and then the easy axis of magnetization is oriented in the longitudinal direction, and then the easy axis of magnetization is oriented in the vertical direction, and further the magnetic layer surface. To 10-6 on average in the vertical direction
The residual magnetic flux density Br ′ in the longitudinal direction and the longitudinal residual magnetic flux density Br ′ measured when the magnetic field is removed after the magnetic field having the direction of the magnetic force line in the direction of 0 ° is applied to orient it and saturated magnetization in the direction perpendicular to the magnetic layer surface is removed. Ratio Br ′ / B of saturation magnetic flux density Bs
and a relationship of 0.2 <Br ′ / Bs <0.6 is satisfied.