JP2843342B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating type magnetic recording medium, and more particularly to an improvement in its electromagnetic conversion characteristics.

[Summary of the Invention]

The present invention provides a magnetic recording medium in which a magnetic layer containing acicular magnetic powder is formed, which defines a coercive force distribution when the inclination angle θ of the applied magnetic field direction with respect to the normal direction of the magnetic layer is changed. By doing so, it is an object of the present invention to provide a method for manufacturing a magnetic recording medium exhibiting high output in both a long wavelength region and a short wavelength region.

[Conventional technology]

For example, as a magnetic recording medium used in an audio tape recorder, a video tape recorder, or the like, a magnetic recording medium in which needle-shaped magnetic powder is oriented in an in-plane direction (in particular, a longitudinal direction of the medium) in a magnetic layer is widely used.

Usually, the orientation treatment in the longitudinal direction is performed by forcibly changing the orientation of the magnetic powder by applying a magnetic field larger than the coercive force of the magnetic powder in the longitudinal direction of the medium using, for example, a permanent magnet or an electromagnet. This is performed so as to be directed in the longitudinal direction of the magnetic support.

[Problems to be solved by the invention]

By the way, in the field of magnetic recording, especially in video tape recorders and the like, higher density recording is required in order to achieve higher image quality and the like, and high output is exhibited from a long wavelength region to a short wavelength region. A magnetic recording medium is required.

However, it is difficult to secure a high output and a high CN ratio particularly in a short wavelength region with the longitudinally oriented magnetic recording media used so far.

Accordingly, the present invention has been proposed in view of such conventional circumstances, and has as its object to provide a magnetic recording medium that exhibits a high output and a high CN ratio over a long wavelength range to a short wavelength range. .

[Means for solving the problem]

The present inventors have conducted various studies in order to achieve the above-mentioned object, and as a result, have obtained a finding that it is effective that the distribution of the coercive force Hc is asymmetrical with respect to the normal direction of the medium. Reached.

The present invention has been completed on the basis of such knowledge, and in a method for manufacturing a magnetic recording medium in which a magnetic layer containing a metal magnetic powder is formed, after the magnetic layer is longitudinally oriented in advance, Orientation, when the coercive force is measured while changing the angle θ between the normal direction and the applied magnetic field direction in one plane perpendicular to the magnetic layer, 0 ° ≦ θ ≦ 30 ° and −60 ° ≦ θ ≦ −30 ° has a local maximum value, −30 ° ≦ θ <0 ° has a local minimum value, and the local maximum value is larger than the coercive force in the in-plane direction so that the local minimum value is smaller. It is characterized by doing.

That is, first, a medium surface (11) such as a tape as shown in FIG. 1 is considered. One vertical plane including the normal Z at the point O on the medium surface (11) [hereinafter referred to as the normal plane]. ] (12) applied magnetic field (He
The angle of inclination in the x) direction (hereinafter referred to as the magnetic field application angle) θ
The hysteresis curve is recorded while changing in the range of -90 ° to 90 °. Therefore, when the direction of the applied magnetic field (Hex) coincides with the normal Z, θ = 0 °, the in-plane direction (x direction)
Θ = 90 ° when matched with θ, and θ = −90 ° when matched with the in-plane direction (x ′ direction).

The slope may be set in an arbitrary direction with respect to the magnetic layer, and the sign of the inclination angle θ is also arbitrary. In any case, the slope will be described later on any slope of the magnetic layer. What is necessary is just to satisfy the characteristics.

However, usually, the slope is determined from the orientation direction of the acicular magnetic powder in the magnetic layer, and is formed on the non-magnetic support (13) with the normal Z, for example, as schematically shown in FIG. The plane including the orientation direction Y of the acicular magnetic powder (15) in the magnetic layer (14) is defined as a slope. The sign of the inclination angle θ is plus when the inclination is in the same direction as the orientation direction (in the case where the inclination is in the clockwise direction with respect to the normal Z) with respect to the normal Z as a reference (0 °). A case of inclining in the opposite direction (a case of inclining counterclockwise in the figure with respect to the normal Z) is regarded as a minus. In this case, generally, the in-plane direction x-
x 'is the tape running direction (in the case of a disk-shaped medium, the tangential direction of the disk).

Next, the coercive force Hc is determined from each hysteresis curve, and plotted against the magnetic field application angle θ, for example, an Hc-θ curve as shown in FIG. 3 (hereinafter referred to as a coercive force curve). Is obtained.

In a normal longitudinally oriented magnetic recording medium, this coercive force curve takes a local minimum value when θ = 0 °, and the position of the local maximum value in the range of −90 ° to 90 ° around θ = 0 ° is left and right. Become symmetric.

On the other hand, in the magnetic recording medium of the present invention, the minimum value is slightly deviated from θ = 0 °, and the maximum value is also 0 ° ≦ θ ≦
The shift is in the range of 30 ° and −60 ° ≦ θ ≦ −30 °, and thus the coercive force curve is asymmetrical.

Further, the maximum value and the minimum value in the coercive force curve are clear, and particularly, the maximum value is larger than the coercive force in the in-plane direction (θ = 90 °).

In order to produce a magnetic recording medium having such characteristics, the needle-like magnetic powder may be oriented obliquely to the surface of the magnetic layer. In this case, however, simply using the oblique orientation method results in insufficient orientation. The peaks of the maximum value and the minimum value tend to be unclear, and the positions of these peaks are out of the above-mentioned range, and the difference between the maximum value and the minimum value tends to be small.

Therefore, in order to surely obtain a magnetic recording medium having the above-described characteristics, it is preferable to perform longitudinal alignment in advance and then perform oblique alignment.

According to this method, the needle-shaped magnetic powder is easily oriented obliquely, the peaks of the maximum value and the minimum value become clear, and the position surely falls within the aforementioned range.

As a method for longitudinal orientation, any of ordinary longitudinal orientation techniques can be adopted. For example, any of a permanent magnet and an electromagnet may be used as long as a DC magnetic field can be applied. As a method for oblique orientation, any method such as a method using a permanent magnet and a method using an electromagnet (DC or AC) may be used. However, when performing the oblique orientation, when the magnets M, M are arranged as shown in FIG. 2, the direction 印 加 of the applied magnetic field must be in the range of 20 ° <ψ <80 ° with respect to the magnetic layer surface. Is preferred.

The magnetic recording medium to which the present invention is applied is a so-called coating type magnetic recording medium in which a magnetic layer is formed by applying needle-shaped magnetic powder together with a binder on a non-magnetic support. The resin to be used may be any resin as long as it is used for this type of magnetic recording medium.

For example, a vinyl chloride-vinyl acetate copolymer,
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer Coalescence, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenolic resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin,
It is a urea-formaldehyde resin or a mixture thereof.

Any needle-shaped magnetic powder can be used as long as it is generally used for this type of magnetic recording medium. Ferromagnetic iron oxide-based magnetic powder, ferromagnetic chromium dioxide-based magnetic powder, ferromagnetic metal-based magnetic powder (so-called Metal powder), iron nitride-based magnetic powder, and the like.

In addition, in addition to these binders and acicular magnetic powders, dispersants, abrasives, antistatic agents, rust inhibitors, lubricants, etc.
Various additives may be added.

The material of the non-magnetic support is not limited, but an organic polymer is suitable in terms of processability, moldability, etc. Among them, polyesters, polyolefins, polyacrylates, polycarbonate, polysulfone, polyamide, and aromatic Group polyamide, polyphenylene sulfide, polyphenylene oxide, polyamideimide, polyimide, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, cellulose acetate, methylcellulose, ethylcellulose, epoxy resin, urethane resin, or a mixture or copolymer thereof. Polymers and the like are suitable. Prior to forming the magnetic layer, these non-magnetic supports are subjected to surface treatment or pre-treatment for the purpose of improving adhesiveness, improving flatness, coloring, preventing static charge, and imparting wear resistance. You may.

The form of the magnetic recording medium may be any of a drum form, a disk form, a sheet form, a tape form, a card form, etc. It is suitable.

[Action]

In the coating type magnetic recording medium using the acicular magnetic powder, i) In the magnetization measurement in the normal plane, assuming that the angle between the direction of the applied magnetic field and the normal direction of the film surface is θ, 0 ° ≦ θ ≦ 30゜ and -60 ° ≦ θ ≦ −30 °, having a maximum value of coercive force; ii) Similarly, having a minimum value of coercive force within a range of −30 ° ≦ θ <0 °; iii. Similarly, the maximum value is larger than the coercive force in the in-plane direction of the film,
By setting the minimum value and the following conditions, high output and high C / N can be obtained in the electromagnetic conversion characteristics, especially in the short wavelength region.

〔Example〕

 Hereinafter, the present invention will be described based on specific examples.

Example 1 First, a magnetic coating material was prepared by dispersing acicular magnetic powder having a coercive force of 1363 Oersted in a binder, and applied to a nonmagnetic support.

Then, as shown in FIG. 4, a longitudinally oriented magnetic field of 2 kGauss was applied by the longitudinally oriented electromagnet (21) while running the coating type magnetic recording medium (20) in the direction of arrow A. The needle-shaped magnetic powder in the magnetic layer was longitudinally oriented.

Further, a DC magnetic field was applied obliquely to the medium surface by a permanent magnet (22) to perform oblique orientation (45 °).

Example 2 A magnetic recording medium was prepared in the same manner as in Example 1 except that the angle of the oblique orientation was 75 °.

Comparative Example 1 A magnetic recording medium was prepared in the same manner as in Example 1, except that only longitudinal orientation was performed using the same longitudinal electromagnet as in Example 1.

Comparative Example 2 First, a magnetic coating material was prepared by dispersing acicular magnetic powder having a coercive force of 1363 Oersted in a binder, and applied to a non-magnetic support.

Next, the needle-like magnetic powder in the magnetic layer was oriented in the direction perpendicular to the film surface by a permanent magnet (5 k Gauss), thereby producing a perpendicularly oriented magnetic recording medium.

Comparative Example 3 First, a needle-shaped magnetic powder having a coercive force of 1363 Oersted was dispersed in a binder to prepare a magnetic paint, which was applied on a non-magnetic support.

Next, a DC magnetic field was applied obliquely to the medium surface by a permanent magnet, and only the oblique orientation (45 °) was performed.

Regarding the magnetic recording media of these examples and comparative examples,
Magnetization measurement [applied magnetic field is applied to the medium running direction (the orientation direction of the needle-shaped magnetic powder) in a normal plane (therefore, the x direction is the medium running direction in FIG. 1). The coercive force was measured while changing). The results are shown in FIG.

Referring to FIG. 5, the coercive force curves of the respective embodiments to which the present invention is applied are bilaterally asymmetric, and the maximum of the coercive force is 0 ° ≦ θ ≦ 30 ° and −60 ° ≦ θ ≦ -30 °. Has a value.

It has a minimum value of coercive force in −30 ° ≦ θ <0 °.

The maximum value is larger than the coercive force in the in-plane direction (90 °).

The minimum value is smaller than the coercive force in the in-plane direction (90 °).

It can be seen that all of the following conditions are satisfied.

On the other hand, in the magnetic recording medium of Comparative Example 1 (longitudinal magnetic recording medium), the coercive force curve is symmetrical, the minimum value is θ = 0 °, and the maximum value is out of the above condition. I understand.

The magnetic recording medium of Comparative Example 2 (perpendicularly oriented magnetic recording medium) only has a local maximum value near θ = 0 °.

Furthermore, the magnetic recording medium of Comparative Example 3 (only oblique orientation)
The peak of the maximum value or the minimum value is unclear, and the position of the peak of the maximum value is also out of the above range.

Thus, the electromagnetic conversion characteristics (dependence of reproduction output on recording wavelength) of the magnetic recording medium of Example 1 and the magnetic recording medium of each comparative example.
Was examined. The results are shown in FIG.

As shown in FIG. 6, the output of the longitudinally oriented magnetic recording medium has a large decrease in the short wavelength region, and the output of the vertically oriented magnetic recording medium has a large decrease in the long wavelength region.

On the other hand, it can be seen that the magnetic recording medium of Example 1 has both of these advantages, and exhibits good reproduction output from a long wavelength range to a short wavelength range.

〔The invention's effect〕

As is clear from the above description, in the magnetic recording medium of the present invention, the coercive force distribution when the inclination angle θ of the applied magnetic field direction is changed with respect to the normal direction of the magnetic layer is defined. A high output can be exhibited in any of a long wavelength region and a short wavelength region, and a high C / N magnetic recording medium can be provided.

[Brief description of the drawings]

FIGS. 1 and 2 are schematic diagrams for explaining a magnetic field application angle when a coercive force curve is obtained, and FIG. 3 is a characteristic diagram showing an example of a coercive force curve of a longitudinally oriented magnetic recording medium. . FIG. 4 is a schematic perspective view of a main part showing an orientation means employed in the embodiment. FIG. 5 is a characteristic diagram showing a coercive force curve of the magnetic recording media prepared in Examples and Comparative Examples. FIG. 6 is a characteristic diagram showing the recording wavelength dependence of the reproduction output of the magnetic recording media prepared in the example and the comparative example.

Claims (1)

(57) [Claims] 1. A method for manufacturing a magnetic recording medium comprising a magnetic layer containing a metal magnetic powder, wherein the magnetic layer is longitudinally oriented in advance, then obliquely oriented, and perpendicular to the magnetic layer. When the coercive force is measured while changing the angle θ between the normal direction and the applied magnetic field direction in the plane, it has local maxima at 0 ° ≦ θ ≦ 30 ° and −60 ° ≦ θ ≦ -30 °, respectively. -30 ° ≦ θ <0 °, and the maximum value is larger than the coercive force in the in-plane direction so that the minimum value is smaller. .