JPH02146106A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium which exhibits high output and high CN in either of long wavelength and short wavelength regions by regulating the coercive force distribution when the angle of inclination in the impressed magnetic field direction with respect to the normal direction of a magnetic layer is changed. CONSTITUTION:The coercive force is measured while the angle theta formed by the normal direction and the impressed magnetic field direction is changed within one plane orthogonal with the magnetic layer of the coating type magnetic recording medium formed with the magnetic layer contg. acicular magnetic powder. A hysteresis curve is then recorded. The coercive force has the max. value in 0 deg.<=theta<=30 deg. and -60 deg.<=theta<=-30 deg. ranges respectively and has the min. value at -30 deg.<=theta<0 deg.. The max. value is made larger than the coercive force in the intra-surface direction (theta=90 deg.) and the min. value is made smaller than the coercive force in the intra-surface direction. The coercive force curve is, therefore, asymmetrical with the normal direction of the medium as a center. The such magnetic recording medium is preferably obtd. by previously orienting the magnetic layer in the longitudinal direction, then diagonally orienting the same.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coated magnetic recording medium.
In particular, it relates to the improvement of its electromagnetic conversion characteristics.

[Summary of the Invention] The present invention provides a magnetic recording medium in which a 6n layer containing acicular magnetic powder is formed, when the inclination angle θ of the direction of the applied magnetic field is changed with respect to the normal direction of the magnetic layer. By defining the coercive force distribution, it is intended to provide a magnetic recording medium that exhibits high output in both the long wavelength region and the short wavelength region.

[Conventional technology]

For example, as magnetic recording media used in audio tape recorders, video tape recorders, etc., media in which acicular magnetic powder is oriented in the in-plane direction (particularly in the longitudinal direction of the medium) in a magnetic layer are widely used.

Normally, this longitudinal orientation treatment is performed by forcibly changing the orientation of the magnetic powder by applying a magnetic field greater than the coercive force of the magnetic powder in the longitudinal direction of the medium using, for example, a permanent magnet or an electromagnet. The magnetic support is oriented in the longitudinal direction.

[Problem to be solved by the invention]

By the way, in the field of magnetic recording5, especially in video tape recorders, etc., there is a demand for even higher density recording in order to achieve higher image quality, etc., and magnetic recording devices that exhibit high output from long wavelength ranges to short wavelength ranges are required. There is a need for a magnetic recording medium that can

However, the longitudinally oriented magnetic recording media used so far have a high output, especially in the short wavelength range.

It is difficult to ensure a high CN ratio.

Therefore, the present invention has been proposed in view of the conventional situation, and it provides high output power and
An object of the present invention is to provide a magnetic recording medium that exhibits a high CN ratio.

(Means for Solving the Problems) As a result of various studies to achieve the above-mentioned object, the present inventors found that coercive force! It has been found that it is effective for the distribution of 1c to be asymmetrical with respect to the normal direction of the medium.

The present invention has been completed based on such knowledge, and provides a magnetic recording medium in which a magnetic layer containing acicular magnetic powder is formed, in which a normal line within a plane orthogonal to the magnetic layer is formed. When the coercive force is measured while changing the angle θ between the direction and the direction of the applied magnetic field, it has maximum values at 0°≦θ≦30″ and 60″≦θ≦−30°, and 306≦θ≦O It has a minimum value in @, and is characterized in that the maximum value is larger and the minimum value is smaller than the coercive force in the in-plane direction.

That is, first, as shown in Fig. 1, the medium surface (
Consider 11). Then, point 0 on this medium surface (11)
A perpendicular plane (hereinafter referred to as a slope) centered on the normal Z in . ) Record the hysteresis curve while changing the inclination angle (hereinafter referred to as magnetic field application angle) θ of the direction of the applied magnetic field (Hex) within the range of -90° to 90° within (12). Therefore, the applied magnetic field (He
When the direction of
When it coincides with the x' force direction, it is θ--90°.

Note that the slope surface may be set in any direction with respect to the 61 magnetic layer, and the sign of the tilt angle θ may be arbitrary. It is sufficient if the characteristics of

However, the slope is usually determined from the orientation direction of the acicular magnetic powder in the magnetic layer, and for example, as schematically shown in FIG. The plane including the orientation direction Y of the acicular magnetic powder (!5) in the magnetic layer (14) is defined as a slope. Also, the sign of the inclination angle θ is the normal Z
is the reference (0°), and if it is tilted in the same direction as the orientation direction (if it is tilted about 1 in the clockwise direction in the figure with respect to the normal Z), plus it is tilted in the opposite direction. (When tilting counterclockwise in the figure with respect to the normal Z)
is a negative value. 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 obtained from each hysteresis curve and plotted against the above magnetic field application angle θ. .) is obtained.

In a normal longitudinally oriented magnetic recording medium, this coercive force curve is θ
The minimum value is taken at -0°, and the position of the maximum value is symmetrical in the range of -90' to 90' with θ=0° as the center.

In contrast, in the magnetic recording medium of the present invention, the minimum value is θ
It deviates slightly from -0°, and the maximum value is also 0″≦θ≦3
0″' and -60″'≦θ≦−30@, and therefore the coercive force curve is left-right asymmetrical.

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

To create a magnetic recording medium with such characteristics,
It is possible to orient the acicular magnetic powder obliquely to the surface of the magnetic layer, but in this case, simply using an oblique orientation method will result in insufficient orientation, and the peaks of maximum and minimum values will likely become unclear. The positions of these peaks are outside the range mentioned above,
The difference between the maximum value and the minimum value also tends to become smaller.

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

According to this method, the acicular magnetic f5) ends are easily oriented obliquely, the peaks of the maximum value and the minimum value become clear, and their positions are reliably within the above-mentioned range.

Note that as a method for longitudinal orientation, any ordinary longitudinal orientation technique can be employed, and for example, either a permanent magnet or an electromagnet may be used as long as a direct current magnetic field can be applied. In addition, any method may be used for oblique orientation, such as a method using a permanent magnet or a method using an IFF magnet (DC or AC).However, when performing oblique orientation, When the magnet MM is arranged as shown in FIG. 2, it is preferable that the direction ψ of the applied 6n field is in the range of 20°<ψ<8o° with respect to the Iff layer surface.

In the magnetic recording medium to which the present invention is directed, an IF layer is formed by applying acicular magnetic powder together with a binder onto a nonmagnetic support. Although this is a so-called coating type magnetic recording medium, any resin used as a binder may be used as long as it is used in this type of magnetic recording medium.

Examples include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, and vinyl chloride-vinylidene chloride copolymer. Acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer.

Methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose MH
body, styrene-butadiene copolymer, polyester resin,
Phenolic resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin.

Such as urea-formaldehyde resin or a mixture thereof.

Any acicular magnetic powder that is normally used in this type of magnetic recording medium can be used, such as ferromagnetic iron oxide magnetic powder, ferromagnetic chromium dioxide magnetic powder 1, ferromagnetic metal magnetic TJL powder ( So-called metal powder), iron nitride magnetic powder, etc. can be used.

In addition to these binders and acicular magnetic powder, the magnetic layer also contains
Various additives such as a dispersant, an abrasive, an antistatic agent, a rust preventive agent, and a lubricant may be added.

The material of the non-6fi support does not matter, but organic polymers are suitable in terms of processability, moldability, etc. Among them, polyester, polyolefins, polyacrylates, polycarbonate, polysulfone, polyamide, aromatic Polyamide, polyphenylene sulfide, polyphenylene oxide, polyamideimide, polyimide, polyvinyl chloride.

Polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, cellulose acetate, methylcellulose, ethylcellulose, epoxy resin, urethane resin,
Alternatively, mixtures and copolymers thereof are suitable. Prior to forming the magnetic layer, these nonmagnetic supports are subjected to surface treatment or pretreatment for the purpose of improving adhesion, improving flatness, coloring, preventing static electricity, imparting wear resistance, etc. You can.

The forms of magnetic recording media are drum-shaped, disk-shaped,
The medium may be in the form of a sheet, tape, card, etc., but since orientation is a problem, it is suitable for application to tape-like media.

[Effect]

In a coated magnetic recording medium using acicular magnetic powder, i) When measuring magnetization on a slope, if the angle between the direction of the applied magnetic field and the normal direction of the film surface is θ, then 0°≦θ≦30. °
and having a maximum value of coercive force within the range of -60°≦θ≦-30°, ii) Similarly, having a minimum value of coercive force within the range of -30°≦θ〈O“, iii) Similarly, by setting the conditions such that the maximum value is larger and the minimum value is smaller than the coercive force in the in-plane direction, high output and high C/N can be obtained in terms of electromagnetic conversion characteristics, especially in the short wavelength range. .

〔Example〕

The present invention will be described below based on specific examples.

First, a magnetic paint was prepared by dispersing acicular magnetic powder of J1363 Oersted in a binder, and this was coated on a non-magnetic support.

Next, as shown in FIG. 4, before the coated magnetic recording medium (20) is moved in the direction of the arrow, a longitudinal direction magnetic field of Gaussian strength is applied to 2 by a longitudinal direction electromagnet (21). was applied to longitudinally orient the acicular magnetic powder in the magnetic layer.

Furthermore, a direct current magnetic field was applied in an oblique direction to the medium surface using a permanent magnet (22) to provide oblique orientation (45').

A magnetic recording medium was prepared according to Example 1 except that the angle of diagonal orientation was 75°.

A magnetic recording medium was produced in accordance with Example 1 except that only the longitudinal direction was performed using the same longitudinal direction electromagnet as in Example 1.

First, a magnetic paint was prepared by dispersing acicular magnetic powder with a coercive force of 1363 oersted in a binder, and this was coated on a non-magnetic support.

Next, the acicular magnetic powder in the 6f1 layer was oriented in a direction perpendicular to the film surface using a permanent magnet (5 Gauss) to produce a vertically oriented magnetic recording medium.

Regarding the magnetic recording media of these Examples and Comparative Examples, magnetization measurements were performed [the applied magnetic field was applied to a slope surface that coincided with the medium running direction (orientation direction of the acicular! n-type powder) (therefore, in FIG. 1, the X direction was the medium running direction). This means that the coercive force was measured while changing it in the normal direction within ). The results are shown in Figure 5.

Looking at this FIG.
The fl force curve is asymmetrical, and ■O゜≦θ≦30
It has a maximum coercive force at ° and -60°≦θ≦-30°.

■Has a minimum value of coercive force at −30”≦θ<Q’.

The maximum value is larger than the holding force in the 0-plane direction (90°).

The minimum value is smaller than the coercive force in the 0-plane direction (90°).

It can be seen that both conditions are satisfied.

On the other hand, in the magnetic recording medium of Comparative Example 1 (longitudinally oriented magnetic recording medium), the coercive force [III line is symmetrical, the minimum value is θ-〇°, and the maximum value also deviates from the previous condition You can see that

Further, the magnetic recording medium of Comparative Example 2 (vertically oriented magnetic recording medium) only has a maximum value near θ=0°.

Therefore, the IF recording medium of Example 1 and the C of each comparative example.
The wavelength dependence of the electromagnetic conversion characteristics of the 11K recording medium was investigated. The results are shown in Figure 6.

Looking at FIG. 6, it can be seen that the longitudinally oriented magnetic recording medium has a large output drop in the short wavelength range, and the vertically oriented magnetic recording medium has a large output drop in the long wavelength range.

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 over a long wavelength range to a short wavelength range.

〔Effect of the invention〕

As is clear from the above explanation, in the magnetic recording medium of the present invention, the coercive force distribution is defined when the inclination angle θ of the direction of the applied magnetic field is changed with respect to the normal direction of the magnetic layer. It is possible to provide a magnetic recording medium that exhibits high output in both the long wavelength region and the short wavelength region, and has a high C/H.

FIG.

FIG. 4 is a schematic perspective view of essential parts showing the orientation means employed in the example.

FIG. 5 is a characteristic diagram showing the coercive force curves of the 411K 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.

Patent applicant: Sony Corporation Agent: Patent attorney Akira Koike (and 2 others)

[Brief explanation of the drawing]

Figures 1 and 2 are schematic diagrams for explaining the magnetic field application angle when determining the coercive force curve, and Figure 3 is a longitudinal direction G.
An example of the coercive force curve of a 11K recording medium is shown in Fig. 1 (in-plane direction) (in-plane direction) Fig. 3 η Fig. 2 Fig. 4 Raw output i@-

Claims (1)

[Claims] In a magnetic recording medium formed with a magnetic layer containing acicular magnetic powder, the angle θ between the normal direction and the direction of the applied magnetic field is varied within a plane perpendicular to the magnetic layer. When the coercive force is measured while A magnetic recording medium characterized in that the maximum value is larger and the minimum value is smaller than the coercive force in the in-plane direction.