JPH01211321A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the orientation rate in the perpendicular direction of a substrate and to obtain a high recording density by using ferromagnetic powder which is planar, has the axis of easy magnetization in the direction perpendicular to the plate plane and has a specific planar ratio (grain size/thickness). CONSTITUTION:The particles which are planar, have the axis of easy magnetization in the direction perpendicular to the plate plane, have 3.5-5.0 planar ratio (grain size/thickness) and are subjected to an orientation treatment in the direction perpendicular to the substrate are used as the particles of the ferromagnetic powder of the magnetic recording medium having a magnetic layer. The packing density of the ferromagnetic powder in the coated film increases but the orientation rate in the direction perpendicular to the substrate by the orientation treatment is insufficient if the planar ratio is smaller than 3.5. The orientation rate increases but the packing density in the medium decreases and the residual magnetization of the magnetic recording medium is so small that the high output is not obtainable if the planar ratio is large than 5. The high-density perpendicular magnetic recording medium having the large residual magnetization and reproduced output is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a magnetic recording medium capable of high-density perpendicular magnetic recording with large residual magnetization.

(Prior Art) Generally, a coated magnetic recording medium is composed of a base made of a polyethylene terephthalate film or the like, and a magnetic layer formed on the base, the main components of which are ferromagnetic powder and a binder.

Conventionally, ferromagnetic powder used in magnetic recording media has been r
-Fe O%CO deposition -γ-Pe O%CO doped -r-FeO5CrOs Acicular magnetic powders such as metal re are widely used, and magnetic recording is performed by a method that uses magnetization in the longitudinal direction in the plane. ing.

In manufacturing a magnetic recording medium by magnetization in the in-plane longitudinal direction, needle-shaped ferromagnetic powder is applied onto a substrate, oriented in the in-plane longitudinal direction in a solenoid, and dried. be able to. Moreover, this orientation can increase the filling rate of magnetic particles in the in-plane longitudinal direction.

However, in a magnetic recording medium obtained by orienting needle-shaped ferromagnetic powder in the in-plane longitudinal direction, when trying to improve recording and reproduction in a high frequency range, the demagnetizing field within the recording medium increases, so recording The problem is that the density cannot be improved that much.

In recent years, in order to significantly improve magnetic recording density, a perpendicular magnetic recording method has been proposed that uses magnetization in a direction perpendicular to the substrate of a magnetic recording medium. A magnetic recording medium based on this method is suitable for high-density digital recording because it does not suffer from the problem of demagnetization within the recording medium even in a high frequency range.

As a magnetic recording medium suitable for this perpendicular recording method,
A coating type recording medium using hexagonal ferromagnetic powder whose axis of easy magnetization is easily oriented in a direction perpendicular to the substrate of the magnetic recording medium is being researched. That is, for example, M-type Babe O or W, which has a flat plate shape and whose axis of easy magnetization is perpendicular to the substrate surface.
BaMe2Fe160゜y (Me is a substitutional metal element)
and those in which some of their atoms are replaced by other atoms, etc., are used. Such perpendicular magnetic recording type magnetic recording media are made by mixing an orthogonal ferromagnetic powder with a binder and coating it on the surface of a non-magnetic substrate, so that the axis of easy magnetization of the ferromagnetic powder in this coating layer is It can be obtained by oriented perpendicularly to the direction of the magnetic field and then dried.

(Problem to be Solved by the Invention) However, in order to obtain such a high-density perpendicular magnetic recording medium, it is necessary to have a high orientation rate in the direction perpendicular to the substrate, a high saturation magnetization, and a large reproduction output. is required. Incidentally, in order to obtain high saturation magnetization, it is generally considered desirable that the filling rate of ferromagnetic powder in the coating film be high.

However, in magnetic recording media using flat ferromagnetic powder, the shape of the ferromagnetic powder that simultaneously satisfies a high orientation rate and a high filling rate has not yet been clarified.

The present inventors conducted intensive research on the above-mentioned problems in obtaining a magnetic recording medium that can simultaneously achieve high recording density and large playback output. In a ferromagnetic powder having an axis of easy magnetization in a direction perpendicular to
It has been found that the above problem can be solved by using a material having the following properties.

The present invention was made based on this knowledge, and an object of the present invention is to provide a high-density perpendicular magnetic recording medium that uses flat ferromagnetic powder as the ferromagnetic powder and has a large residual magnetization and a large reproduction output. That is.

[Configuration of the Invention (Means for Solving the Problems) That is, the magnetic recording medium of the present invention is a magnetic recording medium comprising a magnetic layer formed by coating a magnetic paint containing ferromagnetic powder on a substrate, The particles of the ferromagnetic powder are plate-shaped, have an axis of easy magnetization in a direction perpendicular to the plate surface, and have a plate-like ratio (
It is characterized by having a grain size/thickness of 3.5 to 5.0 and being subjected to orientation treatment in a direction perpendicular to the substrate.

The present invention will be explained in more detail below.

The flat ferromagnetic powder used in the present invention has a particle size of 0
,01~0.3μI, coercive force is 200~20000
, M type (Magnetoplu+gbHe type
) SW-type uniaxially anisotropic Ba ferrite, Ca ferrite, Sr ferrite, Pb ferrite, solid solutions thereof, or ultrafine ferrite powders such as ion-substituted products represented by the following general formula are exemplified.

AO-n(Fe1-1M,)203 (wherein A is at least one element selected from Ba5CasSr and pb, X is Co, T1.Nb, Z
n, Sn+Ni.

Mn, In, Cu, Ge, Zr, Hf, V, Ta,
At least one element selected from A, g, Cr and sb; ■ represents a number of 2 or less; n represents a number from 5.4 to 6.0. ) If the particle size of the above-mentioned ferromagnetic powder exceeds 0.3 μm, it becomes difficult to perform sufficient recording and reproduction in the region of recording wavelengths below 2 μm, where perpendicular magnetization recording is more significant than longitudinal recording.
If it is less than 0.01μ, the magnetization will be small and the reproduction output will be reduced.

Furthermore, if the coercive force of the ferromagnetic powder is higher than 20,000, the head magnetic field will be saturated during recording, and if it is lower than 2,000, it will be difficult to retain the recorded signal.

In addition, if the plate ratio is smaller than 3.5, the filling rate of the ferromagnetic powder in the coating film will be high, but the orientation rate in the direction perpendicular to the substrate due to the orientation treatment will be insufficient, resulting in residual residue on the magnetic recording medium. If the magnetization is small, high output cannot be obtained; conversely, if the plate ratio is greater than 5, the orientation rate will be high, but the filling rate in the medium will be low, and the residual magnetization of the magnetic recording medium will be small, making it difficult to obtain high output. do not have.

The effect of the ferromagnetic powder in the present invention is due only to the shape of the flat ferromagnetic powder, and is not essentially affected by the composition of the magnetic powder.

The magnetic paint used in the present invention usually contains a binder resin, and if necessary, a dispersant, a lubricant,
Additives such as hardeners and abrasives are added.

Examples of the binder resin include vinyl chloride-vinyl acetate copolymer, polyurethane resin, vinyl chloride-vinyl acetate-sulfonated vinyl copolymer, nitrocellulose, polycarbonate resin, polyacrylic resin, polyamide resin, epoxy resin, phenol resin, polyether resin,
Examples include phenoxy resin, melamine resin, vinyl butyral resin, furan resin, and vinyl alcohol resin.

As the dispersant, lecithin, various anionic surfactants, cationic surfactants, nonionic surfactants, silane coupling agents, titanium coupling agents, etc. can be used.

As the lubricant, a higher fatty acid, a higher fatty acid alkyl ester type, a silicone type fluorinated hydrocarbon type, or a mixture thereof can be used.

In addition, polyvalent isocyanate is added as a curing agent for the binder resin used, and CrO, CrO, etc. are added as abrasives.
A, g A hard fine powder having a Mohs hardness of 5 or more, such as O5SiCSZr02, can also be added.

Examples of the solvent used for preparing the paint include solvents that dissolve the binder resin, such as toluene, xylene, cyclohexane, methyl butyl ketone, methyl isobutyl ketone, nitropropane, tetrahydrofuran, and isopropyl alcohol.

Further, as the substrate, in addition to polyethylene terephthalate film, polyamide resin film, etc., non-magnetic metal plates such as aluminum plates can also be used.

Further, as an orientation means for orienting the flat ferromagnetic powder used in the present invention in a direction perpendicular to the substrate, the following method can be used, for example.

■ After applying magnetic paint to the substrate, it is passed through a vertical magnetic field before drying.

■ After applying magnetic paint to the substrate, and before drying, use a doctor blade or the like to move the thinly applied coating film parallel to the substrate while moving it relative to the substrate.

■ After applying magnetic paint to the substrate, let it dry or semi-dry, and pressurize it with a smoother roll or the like.

Note that the achieved orientation rate varies depending on the orientation method, but
It is desirable that at least 70%, preferably 75% or more of the easy axis of magnetization of the ferromagnetic powder be oriented in a direction perpendicular to the substrate. Note that if the orientation rate is low, the residual magnetization of the medium will be small and high output will not be obtained.

The magnetic recording medium of the present invention is manufactured as follows.

First, each of the above-mentioned ferromagnetic powders and a binder resin are dispersed or dissolved in a solvent, and thoroughly mixed and dispersed using a ball mill, sand mill, or the like. In the mixing and dispersing process, various additives such as dispersants, lubricants, abrasives, etc. are added as desired.

Next (iii) If desired, a curing agent such as an isocyanate compound is added to the coating obtained above, and after stirring and mixing thoroughly, it is applied onto a substrate to a thickness of about 1 to 5 μm to form a coating film.

Next, this coating film is subjected to an orientation treatment by a desired means and a drying treatment to obtain the magnetic recording medium of the present invention.

(Function) The magnetic recording medium of the present invention has a flat plate shape, has an axis of easy magnetization in a direction perpendicular to the plate surface, and has a plate ratio (grain size/thickness) of 3.
Since ferromagnetic powder having a particle diameter of 5 to 5.0 is used, the orientation rate and filling rate of the ferromagnetic powder in the coating film are high, and the orientation rate in the direction perpendicular to the substrate is high, thereby achieving high recording density. In addition, the residual magnetization of the magnetic recording medium increases, and high output can be obtained.

(implementation nail) The present invention will be explained in detail below using examples.

In the following examples, the orientation ratio in the direction perpendicular to the substrate and the filling ratio of the ferromagnetic powder in the coating film were determined as follows.

[Orientation rate] The demagnetizing field (4πM) is corrected for the hysteresis curve obtained by applying an external magnetic field up to to k O8 in the direction perpendicular to the substrate of the magnetic recording medium, and the ratio of residual magnetization to saturation magnetization is calculated. The obtained value was taken as the orientation ratio in the direction perpendicular to the substrate.

[Filling factor] The filling factor is -1 when there is no void in the magnetic recording medium, and the saturation magnetization of the magnetic recording medium when the filling factor is -1 is calculated using the saturation magnetization of the ferromagnetic powder, and the actual saturation magnetization is calculated. The filling ratio was obtained by calculating the ratio of the values.

Examples 1 to 3 The ferromagnetic powder was Co-T I-substituted M type Ba-ferrite with a plate ratio of 3.5; Q, 5.0 was used.

The properties of the ferromagnetic powder used are summarized in Table 1.

(Margin below) Table 1 In addition, a magnetic paint was prepared with the composition shown in Table 2.

Table 2 *1: Vinyl chloride-vinyl acetate-vinyl sulfonate copolymer *2 Nistearic acid-butyl stearate mixture *3 Polyvalent isocyanate manufactured by Nippon Polyurethane Co., Ltd. Thoroughly mix each of the above components with a sand glider. After kneading,
It was coated on a polyethylene terephthalate film with a thickness of 9 μm, vertically aligned in a magnetic field of 5 kOe, dried in the magnetic field, and then cured by calendering to obtain a magnetic recording medium.

Examples 4 to 6 ・Using the ferromagnetic powder used in Examples 1 to 3,
The coating composition was adjusted to have the composition shown in Table 3, and magnetic recording media were prepared in the same manner as in Examples 1 to 3.

(Margin below) Table 3 Comparative Examples 1 to 2 As ferromagnetic powder, the plate ratio shown in Table 4 is 3,0; 6,0
Using Co-T I-substituted M-type Ba-ferrite,
Paints were prepared with the same composition as Examples 1 to 3, and
A magnetic recording medium was created using the same method as in Example 3.

(Hereinafter in the margin) Table 4 (hereinafter in the margin) Comparative Examples 3 to 4 Using the ferromagnetic powder used in Comparative Examples 1 to 2, magnetic recording media were prepared using the same paint composition and method as in Examples 4 to 6.

Comparative Examples 5 to 7 As ferromagnetic powder, C with a plate ratio of 3.0; 4.0; 8.0
.

-TI-substituted Ba-ferrite was used. Note that the ferromagnetic powder is the same as that used in Comparative Example 1, Example 2, and Comparative Example 2, respectively. The composition of the paint and the process of forming a film are as follows:
Magnetic recording media were manufactured in the same manner as Examples 1 to 3 and Comparative Examples 1 to 2, except that no orientation treatment was performed.

Table 5 shows the characteristics of the magnetic recording media obtained in each example and comparative example.

In addition, Figure 1 shows the relationship between the plate ratio and orientation rate of the flat ferromagnetic powder in these magnetic recording media, and Figure 2 shows the relationship between the plate ratio and the filling rate of the ferromagnetic powder in the coating film. .

In addition, curve 1 in FIG. 1 shows the results of Examples 1 to 3 and Comparative Examples 1 to 2, curve 2 shows the results of Examples 4 to 6 and Comparative Examples 3 to 4, and curve 3 shows the results of Comparative Examples 5 to 7. Curve 1 in FIG. 2 shows the results of Examples 1 to 3 and Comparative Examples 1 to 2, and curve 2 shows the results of Comparative Examples 5 to 7.

(Left below) Table 5 (Left below) Note that even when other tabular ferromagnetic powder is used instead of Go-TI-substituted M-type Ba-ferrite, the plate ratio is 3.
．． Co-T
Characteristics similar to those of a magnetic recording medium manufactured using I-substituted M-type Ba-ferrite were obtained.

[Effects of the Invention] As explained above, the magnetic recording medium of the present invention has both high recording density and high reproduction output.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the plate ratio of flat ferromagnetic powder and the orientation rate, and Figure 2 is a graph showing the relationship between the plate ratio of flat ferromagnetic powder and the filling rate of ferromagnetic powder in the coating film. It is a graph.

Claims (1)

[Claims] (1) In a magnetic recording medium comprising a magnetic layer formed by coating a magnetic paint containing ferromagnetic powder on a substrate, the particles of the ferromagnetic powder are flat and magnetized in a direction perpendicular to the plate surface. It has an easy axis and a platelet ratio (particle size/thickness) of 3.5 to 5.0.
1. A magnetic recording medium characterized in that an orientation treatment is performed in a direction perpendicular to a substrate.