JPH0714151A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To produce a magnetic recording medium having satisfactory surface smoothness with satisfactory productivity. CONSTITUTION:This magnetic recording medium has <=5nm center line average roughness (Ra) of the surface. In order to control the center line average roughness of the surface of this magnetic recording medium to <=5nm, the particle diameter of magnetic fine particles forming the flux pass layer is preferably regulated to <=120nm. In the case where a two-layered magnetic recording medium is subjected to orientation treatment, in order to attain simultaneous coating, the coercive force of magnetic fine particles in the flux pass layer is regulated to <=300Oe.

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.

[0002]

2. Description of the Related Art Conventionally, a so-called in-plane recording method has been generally used, in which magnetization is formed in a direction parallel to the surface of a magnetic layer film for recording. However, in such a recording method, the recording density could not be increased due to the demagnetization effect. Therefore, in recent years, a perpendicular recording medium using magnetic fine particles such as Ba ferrite capable of high density recording has been developed.
It is about to be put to practical use.

However, a magnetic recording medium in which a single perpendicular recording layer is coated on a substrate is inefficient in writing by a commonly used ring head, and the important improvement in recording density is much less than that of an in-plane oriented medium. Didn't improve.

On the other hand, as described in JP-A-61-34728, γ-Fe2 O3 particles having a needle-like ratio of 2 to 3 and a length of 0.2 μm are used as a first magnetic layer on a substrate. A technique is disclosed in which a layer having isotropic magnetic anisotropy is formed, dried, and then a second magnetic layer having perpendicular magnetic anisotropy is separately provided thereon. With such a configuration, the remanent magnetization state becomes a stable magnetization structure due to the in-plane magnetization of the first magnetic layer and the perpendicular magnetization of the second magnetic layer, and the first magnetic layer functions as a flux path.

[0005]

However, in the above-described conventional magnetic recording medium, γ-Fe2 O3 particles having a needle-like ratio of 2 to 3 and a length of 0.2 μm and large γ-Fe2 O3 particles are used as the magnetic material of the first magnetic layer. Therefore, if the second magnetic layer is thinly applied to a thickness such that the first magnetic layer corresponding to the flux path layer can exert the effect of the flux path, the smoothness deteriorates,
It is not possible to secure excellent electromagnetic conversion characteristics.

In the calendering process after coating and drying the magnetic layer, the thicker the magnetic layer, the better the smoothness, and the thinner the magnetic layer, the rougher the surface. This is because the amount of deformation of the magnetic layer due to the pressure is proportional to the film thickness of the magnetic layer. Therefore, when calendering different thicknesses with the same pressure, the thicker the film, the better the smoothness. Therefore, in the case of the manufacturing method in which coating is performed twice as in the conventional example, the first magnetic layer tends to have poor calendaring. Furthermore, when the second magnetic layer is applied on top of this so as to obtain a flux pass effect, the surface of the magnetic layer becomes rough due to the surface roughness of the flux pass layer, and the smoothness deteriorates.

Further, in the manufacturing method of the conventional example, a drying step is required after the application of the first magnetic layer. This is because, in the case of performing the orientation treatment, if the second magnetic layer is applied simultaneously while the first magnetic layer is not dried, the magnetic fine particles of the first magnetic layer are oriented by the orientation treatment. This is because isotropic magnetic anisotropy cannot be obtained. Therefore, in order for the first magnetic layer of the magnetic recording medium to have isotropic magnetic anisotropy, a drying step is required after coating the first magnetic layer, resulting in extremely poor productivity.

That is, in the conventional example, the purpose is to improve the superiority to the longitudinal recording system, and means for controlling the smoothness of the surface and a method for manufacturing a magnetic recording medium with high productivity. Is not mentioned. The present invention has been made in view of the above circumstances, and provides a magnetic recording medium having good surface smoothness and a method of manufacturing a magnetic recording medium having high productivity.

[0009]

A magnetic recording medium of the present invention comprises a flux path layer mainly composed of first magnetic particles on a support, and second magnetic particles mainly composed on the flux path layer. A magnetic recording medium provided with a magnetic coating layer having a perpendicular magnetization component to the film surface is characterized in that the center line average roughness (Ra) of the surface of the magnetic coating layer is 5 nm or less.

Further, the particle size of the magnetic fine particles constituting the flux path layer is 120 nm or less. Further, the magnetic fine particles forming the flux path layer have a coercive force of 300 Oe or less.

Further, the magnetic fine particles forming the flux path layer have a plurality of easy axes of magnetization. Further, in the method for producing a magnetic recording medium of the present invention, a first magnetic coating material composed mainly of first magnetic fine particles having a coercive force of 300 Oe or less is applied as a flux path layer on a support, and first coating is performed. A step of forming a layer, and before the flux path layer is dried, a magnetic coating layer on the flux path layer is mainly composed of second magnetic fine particles that are easily magnetized in a direction perpendicular to the film surface. And a step of applying a second magnetic coating to form a second coating layer, and a step of drying the first coating layer and the second coating layer to form a flux path layer and the magnetic coating layer. And

[0012]

As described above, the magnetic recording medium of the present invention has a flux path layer mainly composed of first magnetic fine particles on a support and a film surface mainly composed of second magnetic fine particles on this flux path layer. And a magnetic coating layer having a perpendicular magnetization component with respect to the center line average roughness (R
a) is 5 nm or less.

The reproduction output of the magnetic recording medium decreases exponentially with the distance between the recording medium and the head, that is, the spacing amount. Therefore, in the magnetic recording medium of the present invention, the flux path layer is provided in the flux path layer, and the Ra of the magnetic layer of the layer having the perpendicular magnetization component is 5 nm or less and the spacing is small, so that excellent electromagnetic conversion characteristics are secured. It is possible,
The recording medium has improved reproduction output.

There are various methods for obtaining such Ra. For example, the magnetic particles forming the flux path layer preferably have an average particle size of 120 nm or less, and more preferably the particle size range is 40 to 100 nm. . If the particle size is large,
The smoothness deteriorates, the magnetostatic energy on the flux path layer side of the magnetic recording medium becomes non-uniform, and the interface of the flux path layer is disturbed. Therefore, in the present invention, the average particle diameter of the magnetic fine particles is set to 120 nm or less, so that the desired Ra
A magnetic recording medium having

Further, the coercive force of the magnetic fine particles forming the flux path layer is preferably 300 Oe or less. When performing the orientation treatment, the coercive force of 300 Oe or less has the effect of ensuring that the magnetic fine particles are non-oriented to the orientation treatment performed after the coating step, and simultaneous coating is possible. Becomes That is, the magnetic particles in the flux path layer are not oriented even if they are applied simultaneously and subjected to the orientation treatment, so that the magnetization axes of the magnetic particles are oriented in multiple directions, and the flux path layer of the obtained magnetic recording medium is isotropically magnetic. Have characteristics. When the coercive force is greater than 300 Oe, the non-orientation is also affected by the viscosity of the magnetic paint. The simultaneous coating in the present invention means coating the magnetic coating layer before the flux path layer is dried.

Further, the magnetic fine particles forming the flux path layer preferably have a plurality of easy magnetization axes. Since the magnetic fine particles forming the flux path layer have a plurality of easy axes of magnetization, the flux path layer of the magnetic recording medium has an effect that the magnetization can follow a larger number of minute magnetic fields in arbitrary directions. Thus, the flux path effect of the flux path layer is improved, and a magnetic recording medium having further improved output characteristics can be obtained.

Further, in the method of manufacturing a magnetic recording medium of the present invention, when the orientation treatment is carried out, since the magnetic coating made of magnetic fine particles having a coercive force of 300 Oe or less is used for the flux path layer, the orientation treatment carried out after the coating step. On the other hand, it has the effect that the magnetic fine particles of the flux path layer are non-oriented, and the magnetic coating layer and the flux path layer can be applied simultaneously.

Further, in the calendering process performed after coating, the smoother the film, the better the smoothness. Therefore,
Compared to the conventional double coating in which the magnetic flux coating layer is applied after the flux path layer is coated and dried, the conventional calendering process is carried out for each layer formation. Therefore, in the simultaneous coating of the present invention, the surface of the magnetic coating layer is smoothed. Productivity is improved and the number of steps is reduced, so that productivity is improved.

In this manufacturing method, vertical orientation treatment is effective in terms of electrical characteristics of the magnetic coating layer, but short-wavelength output tends to be improved even when in-plane orientation treatment is performed. It is considered that this is because the in-plane orientation of the magnetic coating layer is not perfect, and the magnetic fine particles that are likely to be vertically oriented have many vertical residual components even though they are in-plane oriented. Similarly, the short-wavelength output tends to improve even without alignment treatment, and any of in-plane alignment, vertical alignment, and no alignment treatment is effective.

As the magnetic fine particles in the magnetic coating layer in the present invention, magnetic fine particles which are easily oriented vertically, for example, M-type, W-type or composite type hexagonal ferrite represented by Ba ferrite can be used. For the magnetic particles of the flux path layer, cubic magnetic powder such as magnetite or various spinels can be used. Known binders and other additives can be used.

In order to obtain the effect of the flux pass layer, it is desirable that the thickness of the magnetic coating layer be 1 μm or less. The center line average roughness (Ra) (standard JIS B0
(Based on 601), the Rank Taylor
Hobson's Tarry step was used.

[0022]

The magnetic recording medium of the present invention and its manufacturing method will be described below. (Example 1) As magnetic fine particles, Ba was used in the magnetic coating layer.
Ferrite (coercive force (Hc) 1400 Oe, average particle size (d) 40 nm, saturation magnetization (σ) 60 emu / g, D /
t3), Ni-Zn ferrite (Hc 50 Oe, powder diameter (d) 50 nm, σ 80) in the flux path layer.
emu / g) was used. The Ba ferrite was produced by the glass crystallization method, and the Ni-Zn ferrite was produced by the flux method.

In preparing a magnetic coating material containing these magnetic fine particles, magnetic coating materials having the following compositions are mixed,
Well dispersed. [Magnetic coating layer Magnetic coating composition] Ba ferrite 100 parts by weight Vinyl chloride 3 parts by weight Urethane 4 parts by weight Lubricant 2 parts by weight Abrasive 4 parts by weight [Flux path layer magnetic coating composition] Ni-Zn ferrite 100 parts by weight Vinyl chloride 2 Parts by weight Urethane 4 parts by weight Lubricants 2 parts by weight After the composition is sufficiently dispersed, a polyisocyanate-based curing agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) as a curing agent is added to each resin in the paint. 5 parts by weight was added to 100 parts by weight of the binder. These are 1
A 0 μm PET film was overlaid with a nozzle coater at the same time, and then it was vertically aligned and dried. The obtained film is subjected to calendar treatment, and the obtained raw fabric is cut into a predetermined width,
A magnetic tape for an 8 mm VTR, which is Example 1 of the magnetic recording medium of the present invention, was manufactured.

Example 2 A magnetic recording medium was obtained in the same manner as in Example 1, except that the coating amount was changed by changing the discharge amount of the coating material of the upper flux path layer at the time of coating. It was The magnetic coating layer of this magnetic recording medium was 1.1.
μm, and the flux path layer was 1.4 μm. At this time, even if the film thickness of the upper and lower layers changed, the electrostatic characteristics of the upper and lower layers did not change.

(Embodiment 3) In Embodiment 1, the particle diameter is changed to 120 by changing the condition of the heat treatment for producing fine particles of the magnetic powder of the flux path layer Ni-Zn ferrite.
nm, a magnetic recording medium was obtained by the same method as in Example 1. At this time, the coercive force of the magnetic fine particles in the flux path layer was 190 Oe.

Example 4 A magnetic recording medium was obtained in the same manner as in Example 1, except that the composition of the magnetic coating material for the flux path layer in Example 3 was 8 parts by weight of vinyl chloride and 8 parts by weight of urethane.

(Example 5) In Example 1, Co was added to Ni-Zn ferrite which is a magnetic coating material for the flux path layer to increase the coercive force of the magnetic particles of the flux path layer to 240.
A magnetic recording medium was obtained in the same manner as in Example 1 with Oe set.

Example 6 A magnetic recording medium was obtained by performing in-plane orientation instead of perpendicular recording in Example 1.

(Example 7) In Example 1, instead of Ni-Zn ferrite of the magnetic coating material for the flux path layer, Co substitution type Ba ferrite Hc having uniaxial anisotropy.
A magnetic recording medium was obtained in the same manner as in Example 1 using 200 Oe and a powder diameter of 40 nm. The flux path layer has uniaxial anisotropy, but since the powder coercive force is small, the orientation rate of the flux path layer single layer was 52%, which was almost non-oriented.

(Embodiment 8) A magnetic recording medium was obtained in the same manner as in Embodiment 1, except that the coating amount was changed by changing the discharge amount of the coating material of the upper flux path layer during coating. It was The thickness of this magnetic recording medium was 0.2 μm in the magnetic coating layer and 2.3 μm in the flux path layer. At this time, even if the film thickness of the upper and lower layers changed, the electrostatic characteristics of the upper and lower layers did not change.

(Comparative Example 1) Needle ratio 2 to 3, length 0.2 μ
The γ-Fe ₂ O ₃ fine particles of m, which were made into a paint according to Example 1, were applied onto a PET film, dried, and then subjected to calendaring and curing to form a flux path layer. The film thickness at this time was 2 μm.
Next, a hexagonal plate-shaped microcrystalline Ba ferrite having a diameter of about 0.1 μm, which was made into a paint in accordance with Example 1, was applied to have a coating thickness of 0.5 μm, and dried in a vertical alignment magnetic field. After that, calendering was performed to obtain a magnetic recording medium.

Comparative Example 2 Magnetic Coating Layer The magnetic coating material of Example 1 was applied and vertically aligned to obtain a single-layer magnetic recording medium.

Comparative Example 3 Magnetic Coating Layer The magnetic coating material of Example 1 was applied and in-plane oriented to obtain a single-layer magnetic recording medium.

As described above, Examples 1 to 8 and Comparative Examples 1 to 1
The magnetic recording medium obtained in Comparative Example 3 was cut into a width of 8 mm, and the characteristics and reproduction output of the magnetic recording medium were measured. The results of this measurement are shown in Table 1. In Table 1, the magnetic coating layer is called the upper layer and the flux path layer is called the lower layer. Further, the saturation magnetization amount of each of the magnetic coating layer and the flux path layer in Table 1 is
The saturation magnetization is measured when the magnetic coating material for each layer is applied to a single layer. The reproduction output was measured at room temperature by mounting a sendust thin film head with a gap of 0.2 μm on a modified deck of 8 mm.

[0035]

[Table 1]

[0036]

According to the magnetic recording medium of the present invention, since the surface has good smoothness, a magnetic recording medium having improved output characteristics can be obtained. Further, according to the method of manufacturing a magnetic recording medium of the present invention, the magnetic coating layer and the flux path layer can be coated simultaneously, so that a magnetic recording medium having good smoothness can be easily manufactured.

Claims (5)

[Claims] 1. A flux path layer composed mainly of first magnetic particles on a support, and a magnetic coating layer composed mainly of second magnetic particles on the flux path layer and having a perpendicular magnetization component to the film surface. A magnetic recording medium comprising: a magnetic recording medium having a center line average roughness (Ra) of 5 nm or less on the surface of the magnetic coating layer. 2. The magnetic recording medium according to claim 1, wherein the particle size of the magnetic fine particles forming the flux path layer is 120 nm or less. 3. The magnetic recording medium according to claim 1, wherein the magnetic fine particles forming the flux path layer have a coercive force of 300 Oe or less. 4. The magnetic recording medium according to claim 1, wherein the magnetic fine particles forming the flux path layer have a plurality of easy magnetization axes. 5. A step of forming a first coating layer by coating a first magnetic coating material mainly composed of first magnetic fine particles having a coercive force of 300 Oe or less on a support as a flux path layer, Before the flux path layer is dried, a second magnetic paint composed mainly of second magnetic fine particles that are easy to magnetize in the direction perpendicular to the film surface is applied on the flux path layer as a magnetic coating layer. A method of manufacturing a magnetic recording medium, comprising: a step of forming two coating layers; and a step of drying the first coating layer and the second coating layer to form a flux path layer and the magnetic coating layer.