JPS621113A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which can make effective magnetic recording by the simultaneous utilization of both of vertical and both-faces magnetization components and has excellent surface smoothness by using the magnetic powder of which the squareness ratios in the intra-surface longitudinal direction and perpendicular direction are both >=0.5 and the squareness ratio in the intra-surface direction perpendicular to the intra-surface longitudinal direction is made smaller than the squareness ratio in the intra-surface longitudinal direction. CONSTITUTION:The magnetic powder of the magnetic recording medium formed by providing a magnetic layer contg. hexagonal ferrite powder on a substrate is oriented in the perpendicular direction on the surface and in the intra-surface direction in the inside and the squareness ratios in the intra-surface longitudinal direction and the direction perpendicular to the magnetic layer are larger than 0.5; in addition the squareness ratio in the intra-surface direction perpendicular to the intra-surface longitudinal direction is smaller than the squareness ratio in the intra-surface longitudinal direction. The magnetic powder is the hexagonal ferrite powder which is expressed by the formula MAO.n(Fe1-xMBX)2O3. In the formula, MA denotes the element of at least >=1 kinds among Ba, Sr, Pb, Sb, etc. and controls the coercive force. (n) is preferably 5.0-6.0 and (x) is in a 0-0.2 range. The average grain size of the hexagonal ferrite powder is preferably 0.01-0.3mum and the ratio between the grain size and thickness is >=2:1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic recording medium, and particularly to a coated high-density magnetic recording medium using macrogonal ferrite powder.

[Technical background of the invention and its problems]

A magnetic recording medium is composed of a nonmagnetic support such as polyethylene terephthalate and a magnetic layer provided thereon, the main components of which are magnetic fine particles and a binder. Conventionally, magnetic fine particles include r Fe I Q s, 0 rOH,
Acicular magnetic particles such as metal Fe are widely used.
Magnetic recording is based on a method that uses magnetization in the in-plane longitudinal direction. In manufacturing a recording medium using magnetization in the longitudinal direction of the plane, it is possible to orient the magnetic particles in the longitudinal direction of the plane without causing roughness on the surface of the magnetic layer. The filling rate can be increased. However, with this recording method that uses only magnetization in the in-plane longitudinal direction, when trying to improve recording and reproduction in the high frequency range, that is, to increase the recording density, the demagnetizing field within the recording medium increases, so the recording It is not possible to increase the density to Wakkanai.

In order to solve this problem, a perpendicular magnetic recording method has been proposed in recent years that uses magnetization in a direction perpendicular to the surface of a recording medium. In the perpendicular magnetic recording system, as the recording density increases, the demagnetizing field in the recording medium decreases, so it can be said to be a recording system that is essentially suitable for high-density recording.

As a recording medium suitable for such a perpendicular recording method, a coated recording medium using macrogonal ferrite powder whose axis of easy magnetization is easily oriented in a direction perpendicular to the surface of the recording medium is being researched.

By the way, in the case of a recording medium formed of a coating layer of magnetic particles, the following manufacturing method can be considered. That is, hexagonal ferrite powder such as BaFe, to, etc. is used as the magnetic particles. The reason for using hexagonal fulrite powder is that this ferrite has a flat plate shape, and its axis of easy magnetization is perpendicular to the plate surface, so it can be easily vertically aligned by magnetic field alignment treatment or mechanical alignment treatment. Because you will get it. After mixing such magnetic particles of hexagonal ferrite powder with a binder and coating this on the surface of a non-magnetic support, this coated layer is placed in a magnetic field so that the surface is perpendicular to the direction of the magnetic field. By doing this, the easy axis of magnetization of each magnetic particle is aligned in the direction of the magnetic field, and then the paint is dried to obtain a recording medium suitable for perpendicular magnetic recording.

However, when trying to obtain a perpendicular magnetic recording medium by magnetic field orientation, it is difficult to control the timing of drying in the magnetic field.
It is difficult to obtain a vertically oriented coating film with good reproducibility. Furthermore, if the time during which the magnetic particles are allowed to freely rotate and move under an orienting magnetic field is long, magnetic aggregation of the particles will occur, which will make the coating surface rough, resulting in an increase in noise during recording and reproduction.

[Purpose of the invention]

The present invention has been made to solve the above problems, and enables effective magnetic recording by simultaneously using both perpendicular and double-sided magnetization components in a coated magnetic recording medium using macrogonal ferrite powder. The object of the present invention is to provide a magnetic recording medium that can be used as a magnetic recording medium and has excellent surface smoothness.

[Summary of the invention]

A magnetic recording medium according to the present invention is a magnetic recording medium comprising a magnetic layer containing hexagonal ferrite powder on a substrate, in which the magnetic powder is oriented perpendicularly on the surface and in the in-plane direction inside. The squareness ratio in the in-plane longitudinal direction and the direction perpendicular to the magnetic layer is larger than 0.5, and the squareness ratio in the in-plane direction perpendicular to the longitudinal direction on the side of the lever is smaller than the squareness ratio in the in-plane longitudinal direction. That is.

The present invention will be explained in more detail below.

The magnetic powder in the present invention is a hexagonal ferrite powder, which is represented by the general formula M^s·n(Fe1 zMBz)ton. In the formula, M is Ba, Sr,
Pb.

Ml is In, Co, Ti, Ni, Mn, Ou
, Zn, Ge, Nb, Zr.

At least one of V, Ta, Al, Or, Sb, etc.
Represents more than one element, which controls the coercive force.

Also, n is 5.0 to 6. The range of O1X is preferably O-0.2, and the average particle size of the hexagonal ferrite powder is 0.5
The ratio of particle diameter to thickness of 01 to 0.3 μm is preferably 2:1 or more. It is the length of the diagonal line of the hexagonal plate surface.

Although the method for producing the hexagonal ferrite powder used in the present invention is not particularly limited, for example, the following method can be used. That is, an aqueous solution of metal ions such as iron chloride, barium chloride, or strontium chloride, and optionally a chloride of a substituent element, is brought into contact with an alkaline solution such as NaOH to form a precipitate of metal ions, and after washing with water and drying, the metal ions are heated at a high temperature. Co-precipitation method in which metal ions are crystallized in a high-temperature, high-pressure container in an aqueous solution containing the metal ions, and hydrothermal synthesis method in which metal ions are crystallized in a high-temperature, high-pressure container and heated at high temperatures as necessary (Japanese Patent Laid-Open No. 56-160
328 Publication), a flux method in which a compound containing iron, barium, stronitium, or lead is crystallized with a flux such as Na1l or Ba1lff at high temperature to remove the flux to obtain magnetic particles, BaO+Bl OB t Sio ,
A glass crystallization method in which glass is created from a glass-forming substance such as iron, barium, stronitium, or lead, and a compound containing a substituent element as required, and after crystallization at high temperature, the glass-forming substance is removed to obtain magnetic particles. (Unexamined Japanese Patent Publication No. 56-679
Publication No. 04).

Therefore, the magnetic recording medium of the present invention can be manufactured as follows. That is, the magnetic particles obtained by the above production method or a mixture of magnetic particles obtained by different production methods are made into a paint together with a binder, etc., and applied onto a substrate and passed through a solenoid or a repulsive magnetic field. First, a coating film in which magnetic particles are oriented in the in-plane longitudinal direction is obtained. Next, before this coating film dries, it is mechanically coated with a sear 7 using a smoother or the like to orient the magnetic particles near the surface perpendicularly to the surface. The strength of the magnetic field for orientation in the in-plane longitudinal direction is 500 Oersted or more, preferably 800-3000 Oersted. The strength of the sea 7 for vertical orientation is 500S.
-10Kdyne/c++! ffl, preferably 100
0-5000 dyne/cr/l is good.

In the present invention, there are no particular limitations on the method of mechanically applying the sheet 7. After orienting the magnetic particles in the in-plane longitudinal direction, the sheet 7 is applied with a roll on the coating surface before the coating film dries. It may also be possible to pass through the space. In addition, even after the paint film has dried, the surface of the paint film is dissolved with the solvent used to form the paint, and then mechanically sheared to orient the magnetic particles near the surface perpendicularly to the surface. You may let them. Further, after being oriented in the in-plane longitudinal direction, the coating film is dried. Next, the same paint or a paint having the same composition except for the physical properties of the magnetic particles is overcoated on top of that coating. And similarly mechanically Sea 7
is applied to orient the magnetic particles near the surface perpendicularly to the surface. Alternatively, when performing multiple coatings, the magnetic particles may be oriented perpendicularly to the surface by magnetic field orientation. The thickness of the coating film for vertical alignment in the case of overlapping coatings is preferably about the same thickness as the rad gap width for recording and reproduction, or up to about half that thickness.

The binder used in the present invention is not particularly limited, and various conventionally used thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. Further, the magnetic layer of the present invention may contain abrasives such as aluminum oxide and chromium oxide, lubricants such as various fatty acids and arsenic fatty acid esters, silicone oil, and fluorocarbons, etc., as necessary.

Further, as the substrate used in the present invention, various substrates such as a flexible substrate such as polyethylene terephthalate and a non-magnetic metal substrate can be used.

〔Effect of the invention〕

The magnetic recording medium obtained as described above has an in-plane oriented portion at the bottom of the magnetic layer, which increases the magnetic particle filling rate in the longitudinal direction, that is, the magnetic recording direction, and also increases the vertical orientation in the magnetic layer. The smoothness of the surface is also good because it is not carried out from the substrate surface to the entire surface), and the vertically oriented portion on the surface improves the recording and reproducing output in high frequencies.
Furthermore, by successfully forming a magnetic circuit in the recording medium between the in-plane oriented portion and the perpendicularly oriented portion, it is possible to improve electromagnetic conversion characteristics.

[Embodiments of the invention]

The present invention will be explained in more detail below with reference to Examples.

Example 1 Magnetic particles were produced by glass crystallization method.
Barium ferrite magnetic powder substituted with T, i (average particle size 580^, particle size to thickness ratio 4.5:1, coercive cuff 80
Qe, saturation magnetization 54 emu/g) was used.

Using this Barium 7 Helite magnetic powder, the following composition ratio was thoroughly kneaded to form a paint.

Barium ferrite magnetic particles 100 parts by weight Vinyl chloride-vinyl acetate copolymer 5I polyurethane
10 l chromium oxide fine powder
3I Lubricant 1.51 Dispersant 4I Methyl Ethyl Ketone 40 1 Toluene
40 I cyclohexane 40 parts by weight Add 6 parts by weight of a curing agent to this magnetic paint, apply it on a 15 rope thick polyethylene terephthalate film,
The magnetic particles were passed through a repulsive magnetic field of 0Qe to align them in the plane. Next, before the paint film dries, apply 2000 coats with a smoother.
dyne/crA C7 was applied to vertically align the magnetic particles on the surface of the coating film. Thereafter, it was dried and subjected to surface smoothing treatment. After the coating film was well cured, a slitted magnetic tape with a width of 50% inch was prepared from this film.

The squareness ratio of the obtained magnetic tape was measured using a vibrating sample magnetometer in three directions: the longitudinal direction in the plane, the direction perpendicular to the longitudinal direction in the plane, and the direction perpendicular to the magnetic layer. In addition, the surface smoothness of the obtained tape was measured using a stylus type surface roughness meter, and the recording and playback characteristics in the video band were examined. The results will be described later along with other examples and comparative examples.

Example 2 Barium ferrite magnetic powder substituted with O o -N b produced by hydrothermal synthesis method (average particle size 800k, particle size to thickness ratio 3.7:1, coercive force 1100Qe, saturation magnetization 57emu) /g) was used.

Using this barium fluorite magnetic powder, the same composition ratio as in Example 1 was thoroughly kneaded to form a paint. 6 parts by weight of a curing agent was added to this magnetic paint, which was applied onto a 15 rope thick polyethylene terephthalate plate, and passed through a 2100Qe solenoid to orient the magnetic particles in-plane.

Next, before the coating film dries, 3500 dyn was applied between the twin rolls.
The e/cd sheet 7 was used to vertically align the magnetic particles.

Thereafter, it was dried and subjected to surface smoothing treatment. After the coating film was well cured and post-mortem, the film was slit to a width of 1.5 inches to produce a magnetic tape.

The obtained tape was evaluated in the same manner as in Example 1.

Comparative Example 1 The same magnetic paint used in Example 1 was applied onto polyethylene terephthalate with a thickness of 15 mm, and the magnetic particles were vertically aligned by passing through a magnetic field arranged perpendicular to the magnetic layer surface. A vertically oriented coating film was prepared by drying in a magnetic field. After the coating film was well cured, the film was slit to a width of 50% inch to produce a magnetic tape.

The obtained tape was evaluated in the same manner as in Example 1.

Comparative Example 2 The same magnetic paint used in Example 1 was applied onto a 15-layer thick polyethylene terephthalate plate, and a non-oriented coating was applied! ! dried until. After the coating film was well cured, the film was slit to a width of % inch to produce a magnetic tape.

The obtained tape was evaluated in the same manner as in Example 1. The results for each side are shown below.

Here, Mrx In-plane longitudinal residual magnetization Mry
Residual magnetization in the direction perpendicular to the x-axis in the plane Mrz As seen in the results of the residual magnetization in the direction perpendicular to the magnetic layer film, high output can be obtained due to the good filling condition of the surface and magnetic particles, especially in the low frequency region. Improvements have also been seen. The magnetic layer has in-plane orientation in the longitudinal direction, and the upper part has vertical orientation, so that Mr x/M s>o, st Mr
z/Ms>0.5p MrX/Ms>MYy/Mar
It was found that some effects were observed.

In addition, for strontium ferrite magnetic powder and lead fluorite magnetic powder, the squareness ratio in the in-plane longitudinal direction and the vertical direction is 0.5 or more KL, and the squareness ratio in the in-plane direction perpendicular to the in-plane longitudinal direction is the squareness in the in-plane longitudinal direction. A similar effect was obtained by making the ratio smaller than the ratio.

Claims (5)

[Claims] (1) In a magnetic recording medium formed by coating a magnetic layer containing hexagonal ferrite powder on a substrate, the squareness ratio in both the in-plane longitudinal direction and the perpendicular direction is 0.5 or more, and the in-plane longitudinal direction A magnetic recording medium characterized in that a squareness ratio in an in-plane direction perpendicular to is smaller than a squareness ratio in an in-plane longitudinal direction. (2) The average particle size of hexagonal ferrite powder is 0.01 to 0.
．． The magnetic recording medium according to claim 1, which has a thickness of 3 μm. (3) The ratio of particle size and thickness of hexagonal ferrite powder is 2:1
The magnetic recording medium according to claim 1, which is the above. (4) Coercive force of hexagonal ferrite powder is 200-200
0 Oersted. (5) The magnetic recording medium according to claim 1, wherein the hexagonal ferrite powder having a substitution element for controlling coercive force is represented by the following general formula. M_AO・n(Fe_1_−_xM_B_x)_2O_
In formula 3, M_A is one of Ba, Sr, and Pb, and M_B is Ir, Co, Ti, Ni, Mr, Cn, Zr, Nb, and V.
, Ta, Sb, Al, and Cr, x represents 0 to 0.2, and n represents 5.0 to 6.0.