JPH01251425A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the desorption of polishing agent particles and to enhance traveling durability and reliability by lowering the hardness of a 1st magnetic recording layer and adding the polishing agent having a specific grain size to the 2nd magnetic recording layer. CONSTITUTION:The 1st magnetic recording layer (A) contg. acicular ferromagnetic powder (a) and the 2nd magnetic recording layer (B) contg. hexagonal ferromagnetic powder (b) having the axis of easy magnetization perpendicular to the planar plane are formed on a substrate. The polishing agent (e.g.: Al2O3) having the average grain size larger than the film thickness of the layer B is added to the layer B so that the layer A is formed to the hardness lower than the hardness of the layer B. The adjustment of the hardness of the layer A is executed by selecting the binder and controlling the amt. of the additive and the orientation of the component B is executed by the orientation treatment of the layer B. Co-deposited gamma-ferrite, etc., are usable for the component (a) and Co-Ti substitution type Ba ferrite, etc., are usable for the component (b).

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a magnetic recording device capable of high-density recording that provides high reproduction output in a wide range of wavelengths from short wavelengths to long wavelengths. Regarding the medium.

(Prior Art) In recent years, magnetic recording media have come into widespread use as recording media for recording large amounts of information in various fields such as audio, video, and computer applications.
Along with this, there is a demand for further improvement in recording density.

In response to these demands, for example, ultrafine hexagonal ferromagnetic powder, such as hexagonal ferrite powder, in which the axis of easy magnetization is perpendicular to the plate-like surface of the particle, is used to create a magnetic layer in which the plate-like surface is A perpendicular magnetization recording system that uses residual magnetization perpendicular to the plane of the magnetic recording medium, which is oriented parallel to the plane of the magnetic recording medium, is attracting attention.

However, although magnetic recording media obtained using such ultrafine hexagonal ferromagnetic powders can obtain high reproduction output in the short wavelength region where the recording wavelength is about 1 μm or less,
It has been found that what causes the characteristic that high reproduction output cannot be obtained when used for recording in the long wavelength range. For this reason, when recording and reproducing signals in a long wavelength range such as audio signals and color signals on, for example, a VTR tape, there is a problem in that sufficient recording becomes difficult.

As a way to compensate for these drawbacks, the magnetic recording layer has a two-layer structure, and the lower layer is made of acicular ferromagnetic powder such as metal magnetic powder or oxide magnetic powder, which is advantageous for recording and reproducing in the long wavelength range. A two-layer magnetic recording medium has been proposed, in which a magnetic layer is formed using a magnetic layer made of a hexagonal ferromagnetic powder, which is advantageous for recording and reproducing in a short wavelength range.

Although such a two-layer magnetic recording medium is effective for recording and reproducing over a wide range of wavelengths from short wavelengths to long wavelengths, there are many problems that must be solved.

For example, in order to enable recording of short wavelength signals, the gap of the magnetic head used must be 0.3 μm.
It is necessary to make the width narrower as shown below, which makes it difficult to apply a long wavelength signal to the deep layer of the magnetic layer. In order to provide a sufficient recordable magnetic field to the lower magnetic layer responsible for recording long wavelength signals, the upper magnetic layer must be extremely thin.

However, by reducing the thickness of the upper magnetic layer, the inorganic additives contained in the magnetic layer, especially the abrasive, must be present on the surface, and if a relatively large diameter one is used, the abrasive may detach. There is a problem in that running durability and reliability are reduced.

It is also conceivable to reduce the particle size of the abrasive according to the thickness of the magnetic layer, but if a fine particle size is used, a problem arises in that the polishing and cleaning performance for the magnetic head deteriorates.

(Problems to be Solved by the Invention) As described above, a magnetic recording medium with a two-layer structure consisting of a magnetic layer made of acicular ferromagnetic powder and a magnetic layer made of hexagonal ferromagnetic powder can be used in a short wavelength range to a long wavelength range. Although it is superior in terms of effectively recording and reproducing a wide range of wavelengths up to At the same time, a problem arises in that the cleanliness of polishing the magnetic head also deteriorates, such as head clocking phenomenon occurring.

The present invention has been made to address the problems of the conventional technology, and it is possible to obtain high output over a wide range of wavelengths from short wavelengths to long wavelengths, and to improve running durability and reliability. The purpose is to provide an excellent magnetic recording medium.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a first magnetic recording layer formed by coating an acicular ferromagnetic powder together with a binder component on a substrate, and a first magnetic recording layer. A magnetic recording medium having a second magnetic recording layer formed by coating thereon a hexagonal ferromagnetic powder whose easy axis of magnetization is perpendicular to the particle plate plane together with a binder component. The layer contains an abrasive having an average grain size larger than the thickness of the second magnetic recording layer, and the hardness of the first magnetic recording layer is smaller than the hardness of the second magnetic recording layer. There is.

Examples of the acicular ferromagnetic powder used in the first magnetic recording layer in the present invention include γ-Pe203, Co-γ-
Examples include oxide ferromagnetic powders with an acicular structure such as Fe203, and metal ferromagnetic powders with an acicular structure such as CrO2 and Co-Pe alloys, and the particle size of these acicular ferromagnetic powders is generally expressed by the long sleeve diameter. 0.1 μm to 1 μm is suitable.

Furthermore, the hexagonal ferromagnetic powder used in the second magnetic recording layer has uniaxial anisotropy in which the axis of easy magnetization is perpendicular to the particle plate surface, and has a coercive force of 2000 e.
Examples include ultrafine powder of ferrite such as M-type or W-type Ba ferrite, Sr ferrite, Ca ferrite, PB ferrite, or solid solutions thereof, or ion substituted products represented by the following general formula, with a particle size of about 20,000 e. .

General formula: AO・口(Fe14MI11)203 (in the formula,
A is any one element of Ba, 5rSCa, Pb, H is Zn, Co5Tl, old, Mns Ins CL
I% Ges Nb5Sn, Zr, lIr5Aβ, etc., at least an element of IMi, m is 0 to 2,
n represents a number from 5.4 to 8.0, respectively. However, H
When is an element with a valence of 2 or 4 or more, the question is the combination of two or more elements whose average valence is 3.

) These hexagonal ferromagnetic powders have a hexagonal plate-like crystal structure, and have an average particle size in the range of 0.03 μm - (1.1 μm), where the length of the diagonal of the plate surface is taken as the particle size. The ratio of the diagonal length of the hexagonal plate surface to the thickness, that is, the plate ratio, is preferably in the range of 3 to 5.

The first magnetic recording layer in the present invention is produced, for example, as follows.

That is, first, the acicular ferromagnetic powder and the binder are dispersed or dissolved in a solvent, and the mixture is thoroughly mixed and dispersed using a ball mill, sand mill, etc. to produce a magnetic paint. Dispersants, lubricants, etc. may be added to this magnetic paint as desired.
Further, appropriate amounts of various additives such as antistatic agents such as graphite powder and carbon black may be added.

Next, after applying this magnetic paint onto the substrate, it is subjected to orientation treatment, etc., if desired, and then dried to produce a first magnetic recording layer.

As the binder component for producing the above-mentioned magnetic paint, it is possible to use various conventionally known binder components, such as polyurethane resin, polyester resin, polycarbonate resin, polyacrylic resin, Examples include epoxy resins, phenol resins, vinyl chloride resins, vinyl acetate resins, and mixtures or copolymers thereof. Examples of lubricants include lauric acid, palmitic acid, and stearic acid, and examples of dispersants include lecithin and various surfactants.

The hardness of this first magnetic recording layer is adjusted to be smaller than that of the second magnetic recording layer, and its thickness is 1 μm.
It is preferable to set it to about 5 micrometers.

The hardness of the coating film is adjusted, for example, by using a binder component with relatively low hardness or by adjusting the amount of additives. The hardness of the first magnetic recording layer varies depending on the hardness of the second magnetic recording layer, but it is preferably in the range of approximately 2H to 8 on the Empi hardness scale.

Further, for the second magnetic recording layer, similarly to the first magnetic recording layer described above, a magnetic paint is prepared by first uniformly dispersing hexagonal ferromagnetic powder in the various binder components described above. An abrasive is added as an essential component to the magnetic paint for the second magnetic recording layer. As this polishing agent, TlO2, Cr
Inorganic powders having a Mohs hardness of 5 or more, such as 203, A, g 203 and SiC5Zr02, are suitable, and the amount used is preferably about 0.5 to 10 parts by weight per 100 parts by weight of the magnetic powder. The abrasive used here has an average particle size of, for example, about 0.1 μm to 2.0 μm, which is larger than the film thickness of the second magnetic recording layer.

Next, the above-mentioned magnetic paint is applied onto the first magnetic recording layer, and an orientation treatment is performed, for example, by placing the coating film in a magnetic field perpendicular to the substrate surface to orient the axis of easy magnetization of the magnetic powder in the direction of the magnetic field. Then, after drying, the surface is smoothed by calendering or the like.

By this surface smoothing treatment (S), the abrasive particles contained in the second magnetic recording layer are embedded in the first magnetic recording layer, are sufficiently retained by the binder component, and are prevented from detaching.

The film thickness of the second magnetic recording layer maintains short wavelength recording characteristics,
Moreover, it is necessary to make it thin so as not to deteriorate the long wavelength characteristics, and a thickness of about 0.1 μm to 0.5 μm is suitable, for example. If the thickness of the second magnetic recording layer is less than 0.1 μm, the recording magnetic field in the short wavelength region may reach the first magnetic recording layer, and if it exceeds 0.5 μm, recording in the long wavelength region may occur. There is a possibility that the magnetic field will not reach the first magnetic recording layer sufficiently. Further, although the hardness varies depending on the hardness of the first magnetic recording layer, it is preferably in the range of approximately 5H to 9H or more in terms of Empi hardness.

Also, this f? A small amount of an antistatic agent as described above may be added to the magnetic recording layer of S2, but as long as the conductivity of the first magnetic recording layer is ensured, charging can be prevented even if almost no conductive powder is added. Therefore, it is possible to increase the filling rate of the magnetic powder in the magnetic recording layer of division 2 and improve the recording and reproducing output. Note that this conductivity can also be ensured by the base.

(Function) -S: In order to prevent the sliding surface of the magnetic head from becoming rough and to maintain a good contact state at all times, the magnetic recording layer must have a certain level of abrasiveness against the head. Therefore, the abrasive must be contained in the magnetic recording layer and must appear on the surface of the magnetic recording layer.

In the magnetic recording medium of the present invention, the second magnetic recording layer contains an abrasive having an average grain size larger than the thickness of the second magnetic recording layer. In addition, the hardness of the first magnetic recording layer is made smaller than the hardness of the second magnetic recording layer, so that the abrasive contained in the second magnetic recording layer can be removed during calendering, which is a surface finishing process. The particles can be easily embedded into the first magnetic recording layer. Therefore,
The abrasive can easily appear on the surface of the magnetic recording medium to ensure sufficient abrasiveness to the magnetic head, and the abrasive can be sufficiently retained in the binder to prevent detachment, improving running durability and reliability.

The present invention allows some of the abrasive particles contained in the second magnetic recording layer to be embedded into the first magnetic recording layer during calendering, etc., so that the abrasive particles can be absorbed even when the second magnetic recording layer is thin. It is characterized by sufficient binder retention.

Therefore, the hardness of the first magnetic recording layer after the abrasive is embedded in the first magnetic recording layer does not necessarily have to be low.

Furthermore, even if the thickness of the second magnetic recording layer made of a large-scale ferromagnetic powder whose easy axis of magnetization, which is advantageous for short-wavelength signals, is perpendicular to the plate-like surface of the particles is made sufficiently thin, the removal of the abrasive may occur. Since the occurrence of this phenomenon is prevented, even when a narrow gap magnetic head is used, it is possible to sufficiently provide a long wavelength signal to the first magnetic recording layer made of acicular ferromagnetic powder. Therefore, high output can be obtained in a wide range of wavelengths from short wavelengths to long wavelengths.

(Example) Next, examples of the present invention will be described.

Example First, the following composition was thoroughly mixed and then dispersed for an additional hour using a sand grinder to prepare a magnetic paint for a first magnetic recording layer.

(Coating components for the first magnetic recording layer) Coating - Ferrite powder 100 parts by weight (average particle size 0.5μ11) Carbon black 4 Lecithin 31 Polyurethane resin 12 Vinyl chloride vinyl acetate copolymer resin 6 Methyl ethyl ketone
80/l cyclohexane 80
〃Toluene 80g/Next, the obtained magnetic coating for the first magnetic recording layer was coated to a thickness of 50μ.
A first magnetic recording layer was prepared by applying the mixture onto a polyester film having a thickness of 3 μm and drying it to a thickness of 3 μm after drying.

Note that the hardness of the first magnetic recording layer is 51 on the Empi hardness.
It was 1.

Next, the following composition was thoroughly mixed and then dispersed for another 2 hours using a sand grinder to produce a second magnetic coating for a magnetic recording layer.

[Magnetic paint components for second magnetic recording layer] Co-Tl substituted Ba ferrite powder 100 parts by weight (average particle size 0.05 μm, plate ratio 3, coercive force 6000e) An203 powder 4 (average particle size 0, 5 μl) Lecithin 3 // Stearic acid 2 // Polyurethane resin 8 Vinyl chloride-vinyl acetate copolymer resin 8 // Methyl ethyl ketone
8011 cyclohexane
8011 toluene 8
0 Next, an isocyanate compound is added as a curing agent to the obtained magnetic coating for the second magnetic recording layer and kneaded, and then a film with a dry film thickness of 0 is applied on the first magnetic recording layer described above. .3 μm, and then placed in a magnetic field perpendicular to the surface of the magnetic recording layer for orientation treatment, dried, and calendered to smooth the surface. A magnetic recording layer was prepared, and the intended magnetic recording medium was obtained.

The hardness of the second magnetic recording layer is 8H in terms of hardness.
Met.

Comparative Example 1 The blending ratio of polyurethane resin, hydrochloric acid, and copolymer resin as binder components in the magnetic paint for the first magnetic recording layer in the above example was the same as that of the magnetic paint for the first magnetic recording layer. A two-layer magnetic recording medium was manufactured under the same conditions except for the above. The hardness of the first magnetic recording layer of this magnetic recording medium was 411 in Empi hardness.

Comparative Example 2 A magnetic recording medium was produced under the same conditions as in Comparative Example 1 except that the 1203 powder contained in the second magnetic recording layer in Comparative Example 1 had an average particle size of 0.1 μm.

The magnetic recording media obtained in the above Examples and Comparative Examples were
The running durability, polishing and cleaning properties for magnetic heads, and output characteristics in each wavelength range were measured. The measurement was performed using a VH3 type VTR, and evaluated the still durability and the output drop after 30 minutes at a recording wavelength of λ-0 and 1 μm. The results are shown in the table below.

In addition, the still durability time is -3 compared to the initial recording and playback output.
, the time it takes for the voltage to drop to 0 dB.

As is clear from the results in the preceding table, in the magnetic recording medium of this example, relatively large-diameter abrasive particles are pressed into the first magnetic recording layer, and the binder of the first magnetic recording layer sufficiently absorbs the particles. Since the abrasive particles were maintained at a high temperature, there was almost no detachment of the abrasive particles, resulting in excellent durability. In addition, since sufficient abrasive particles appear on the surface layer of the magnetic recording medium, it has excellent abrasiveness against magnetic heads, and can be used for long periods of time in a wide range of wavelengths from short wavelengths to high wavelengths. Excellent playback output was obtained.

On the other hand, in the magnetic recording medium of Comparative Example 1, the abrasive particles were detached, and in the magnetic recording medium of Comparative Example 2, the abrasive particles were made finer, which deteriorated the abrasiveness to the magnetic head, and the durability of the magnetic recording medium deteriorated. and had poor reliability.

In addition, in the magnetic recording medium according to this example, since the grain size of the abrasive particles is made larger than the film thickness of the second magnetic recording layer, almost all of the abrasive particles contained in this upper layer appear on the surface layer. Therefore, it has become possible to easily improve the polishing cleanliness of the magnetic head. Furthermore, since the hardness of the lower layer is lower than that of the upper layer, the surface can be easily smoothed during the final calendering process.

[Effects of the Invention] As is clear from the above examples, the magnetic recording medium of the present invention can obtain high reproduction output in a wide range of wavelengths from short wavelengths to long wavelengths, and also has a high reproduction output due to the abrasive particles. It also prevents detachment and has excellent running durability and reliability.

Applicant: Toshiba Corporation Agent Patent Attorney Suyama Sa

Claims (1)

[Claims] (1) A first magnetic recording layer formed by coating an acicular ferromagnetic powder together with a binder component on a substrate, and an axis of easy magnetization on this first magnetic recording layer that is perpendicular to the plate-like surface of the particles. A magnetic recording medium having a second magnetic recording layer formed by applying hexagonal ferromagnetic powder together with a binder component, wherein the second magnetic recording layer has an average particle diameter equal to the thickness of the second magnetic recording layer. A magnetic recording medium containing a larger abrasive and having a hardness of the first magnetic recording layer smaller than a hardness of the second magnetic recording layer.