JPH03224133A - Production of perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having high perpendicular orientation of magnetic particles and excellent electromagnetic conversion characteristics at high efficiency and low cost by orienting a magnetic coating film in a perpendicular magnetic field and then applying a specified AC magnetic field for demagnetization while the magnetic coating film is not dried. CONSTITUTION:A magnetic coating material is applied on a nonmagnetic supporting body, on which a perpendicular magnetic field is applied to orient the magnetic particles. Then an AC magnetic field of >=300 Hz frequency containing the perpendicular component to the film is applied on the film for demagnetization while the magnetic coating film is not dried. The film is then dried to form the magnetic layer. Namely, by applying an AC magnetic field having the perpendicular component to the coating film after orientation, mag netic particles showing the magnetic pole direction up or down are uniformly dispersed in the film to give apparent demagnetized state of the film as a whole. By this method, a recording medium having extremely high perpendicular orienta tion of magnetic particles and excellent electromagnetic conversion characteristics can be produced at high efficiency and low cost.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes and magnetic disks having a coated magnetic layer on a non-magnetic support, and particularly to magnetic recording media such as magnetic powders in the magnetic layer. The present invention relates to a method for producing a perpendicular magnetic recording medium in which the axis of easy magnetization is oriented perpendicularly to the surface of the support.

[Conventional technology]

The magnetic recording medium that uses the perpendicular magnetic recording method is γ-Fe.
20: Enables dramatically higher density recording than conventional magnetic recording media that employ the general-purpose longitudinal magnetic recording method, which uses magnetic powder made of acicular particles such as powder or metallic iron powder as the recording element. As such, research and development has been actively conducted in recent years.

In particular, perpendicular magnetic recording media that have a coated magnetic layer containing hexagonal ferrite powder, typically Ba ferrite powder, have problems in corrosion resistance and durability, unlike perpendicular magnetic recording media that have a magnetic layer made of a thin metal film. It is attracting attention because of its excellent reliability and suitability for mass production.

Incidentally, the electromagnetic conversion characteristics of such a coated perpendicular magnetic recording medium largely depend on the squareness of the medium, and are improved as the squareness in the vertical direction becomes higher. Therefore, in boat fishing, when coating a magnetic coating on a non-magnetic support to form a magnetic layer, N-
3. By applying a magnetic field perpendicular to the coated surface using opposed magnets, the magnetic particles are oriented so that their axis of easy magnetization is perpendicular to the coated surface, and the above-mentioned vertical square shape is formed. A method has been adopted to increase the

[Problem to be solved by the invention]

However, in the above method, the magnetic particles once oriented by the perpendicular magnetic field are affected by the demagnetizing field generated in the medium and the degree of orientation decreases. It is necessary to dry the magnetic coating film to prevent the rotational movement of the magnetic particles.

However, if this drying is carried out rapidly in a short period of time, such as by spot drying by blowing hot air, the surface smoothness of the magnetic layer deteriorates, resulting in a decrease in electromagnetic conversion characteristics. On the other hand, in order to dry slowly and over a long period of time, it is necessary to significantly slow down the coating speed or set the orientation magnetic field region to be extremely long. Equipment costs will be required.

Therefore, with the above-mentioned conventional means, there is a problem in that in order to obtain a magnetic recording medium with a high degree of perpendicular alignment, either the medium characteristics or the production cost must be sacrificed.

In view of the above-mentioned circumstances, an object of the present invention is to provide a method for producing a perpendicular magnetic recording magnetic recording medium with extremely high degree of perpendicular orientation of magnetic particles and excellent electromagnetic conversion characteristics with high efficiency and at low cost. It is an object.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors found that when the magnetic layer is demagnetized by a specific means following the normal vertical magnetic field orientation performed after applying magnetic paint, It is possible to prevent the axis of easy magnetization of the magnetic particles from falling in the in-plane direction, resulting in a high degree of vertical orientation, and there is no need to perform rapid drying or reduce the coating speed of the magnetic paint as in the case of conventional methods, which improves the media properties. They found a way to achieve both productivity and productivity, and came up with this invention.

That is, in this invention, a magnetic paint is applied onto a non-magnetic support, a magnetic field is applied perpendicular to the coated surface to orient the magnetic particles, and then the coated surface is coated while the magnetic coating is not dry. A frequency of 300 H with a magnetic field component perpendicular to
The present invention relates to a method of manufacturing a perpendicular magnetic recording medium, characterized in that a magnetic coating film is demagnetized by applying an alternating current magnetic field of z or more, and then dried to form a magnetic layer.

Further, in the above manufacturing method of the present invention, a particularly preferred embodiment is such that the magnetic particles used are macrogonal ferrite particles.

[Structure and operation of the invention]

In the manufacturing method of the present invention, a magnetic coating film formed by coating on a non-magnetic support such as a polyester film is subjected to perpendicular magnetic field orientation similar to that used in manufacturing magnetic recording media of the conventional perpendicular magnetic recording method. However, in the undried state after this orientation, an alternating current magnetic field is further applied as described above to demagnetize the magnetic coating film.

That is, due to the vertical magnetic field orientation, all the magnetic particles in the magnetic coating film are oriented so that their axes of easy magnetization are perpendicular to the coating surface, but after this orientation, the magnetic particles have a magnetic field component perpendicular to the coating surface. When an alternating current magnetic field is applied, magnetic particles whose magnetic pole directions are upside down are evenly present in the coating film, and the magnetic coating film as a whole is demagnetized.

Therefore, according to this method, the degree of perpendicular orientation is prevented from decreasing due to the demagnetizing field when a magnetic layer is continuously formed while the nonmagnetic support is running, so the magnetic coating film is dried within the orientation magnetic field. (It is no longer necessary to perform short drying times due to conventional spot drying or long drying times due to extremely low coating speeds.) It can be avoided and
It is possible to form a magnetic layer at a coating speed comparable to that of manufacturing magnetic recording media using the in-plane magnetic recording method, and high productivity can be ensured.

The alternating current magnetic field used for the above demagnetization must reverse the magnetic moment faster than the rotation period of the magnetic particles within the magnetic coating in order to prevent the magnetic particles from rotating following changes in the magnetic field. , from this point the frequency is set to 300. Set above Hz. The upper limit of frequency is 5.000 Hz
An alternating magnetic field with a frequency higher than this is difficult to generate, and the degree of vertical orientation also reaches saturation, so that no further improvement can be expected. The strength of this alternating magnetic field is preferably about 0.5 to 3 times the coercive force (Hc) of the magnetic particles used.

On the other hand, in the manufacturing method of the present invention, the vertical magnetic field orientation applied after applying the magnetic paint is N-3 as in the conventional method.
This can be done using various vertical magnetic field generators such as opposed magnets and solenoid coils.

It has been previously proposed that the vertical magnetic field orientation itself be performed using an alternating magnetic field, but in this case, the maximum magnetic field that orients the magnetic particles so that the axis of easy magnetization is perpendicular to the coated surface is continuously However, during the reversal process of the magnetic field, it acts in a direction that tilts the axis of easy magnetization in the plane, and therefore a higher degree of orientation cannot be achieved compared to normal orientation due to a fixed magnetic field.

In addition, in such orientation using an alternating magnetic field, since the magnetic particles are rotated and oriented by the magnetic field, it is necessary to set the frequency to usually about 100 Hz or less to slow down the reversal period of the magnetic moment. It is essentially different from the alternating current magnetic field applied for said demagnetization.

The magnetic paint used in this invention is prepared by dispersing and mixing magnetic powder, a binder, and various additives added as necessary in a suitable organic solvent according to a conventional method.

The above-mentioned magnetic powder is not particularly limited, but includes hexagonal ferrite powder having an axis of easy magnetization perpendicular to the particle plate surface, such as barium ferrite powder, strontium ferrite powder, lead ferrite powder, calcium ferrite powder, etc. It is suitable for use in perpendicular magnetic recording media.

As the above-mentioned binder, any binder conventionally known for use in magnetic layers of magnetic recording media can be used, such as vinyl chloride-vinyl acetate copolymers, cellulose resins, polyurethane resins, and polyvinyl butyral resins. Examples include resins, polyvinyl acetal resins, polyester resins, isocyanate compounds as crosslinking agents, radiation curable resins, and two or more of these may be used in combination.

Examples of the above additives include dispersants, lubricants, abrasives, antistatic agents, fillers, and the like. As the organic solvent, conventionally used organic solvents such as toluene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, and ethyl acetate can be used alone or in combination of two or more.

In order to manufacture a perpendicular magnetic recording type magnetic recording medium using the manufacturing method of the present invention, a non-magnetic support such as a polyester film is continuously run, and the above-mentioned magnetic paint is applied to the surface according to a conventional method. After that, the perpendicular magnetic field orientation described above is performed on the subsequent stage, and the undried area of the magnetic coating film is demagnetized by the alternating current magnetic field, and then the magnetic coating film is dried and hardened in a drying oven etc. to form a magnetic layer. After forming and then performing surface treatment such as calendering as necessary,
All you have to do is cut it to the desired width, size, and shape.

(Effects of the Invention) According to the manufacturing method of the present invention, a magnetic coating film formed by coating on a non-magnetic support is subjected to normal perpendicular magnetic field orientation, and then the magnetic coating film is undried. Since demagnetization is performed by applying an alternating magnetic field of In addition to avoiding deterioration, there is no need to reduce the coating speed, and as a result, a perpendicular magnetic recording medium with an extremely high degree of perpendicular orientation of magnetic particles and excellent electromagnetic conversion characteristics can be obtained with high efficiency and at low cost.

Further, in the manufacturing method of the present invention, if hexagonal ferrite particles are used as the magnetic particles, a particularly excellent magnetic recording medium for perpendicular magnetic recording systems can be obtained.

〔Example〕

Next, the present invention will be specifically explained using examples.

In addition, in the following, parts mean parts by weight.

Example 1 CX-Al! 2Q3 powder 1 part methyl isobutyl ketone 80 parts toluene
After mixing and dispersing 80 parts of the above composition in a ball mill for 3 days, 8 parts of oleyl oleate and 2.5 parts of a trifunctional isocyanate compound (trade name Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) were added, and A magnetic paint was prepared by mixing and dispersing for 2 hours.

This magnetic paint was applied onto a continuously running polyester film with a thickness of 75 μm at a coating speed of 40 m/min so that the thickness after drying was approximately 3 μm, and then N -3 A perpendicular magnetic field is oriented with a perpendicular magnetic field strength of 4 Oersteds (Oe) using opposing magnets, and then an alternating current perpendicular magnetic field of Oersteds (Oe) with a frequency of 500 Hz and a perpendicular magnetic field strength of 2 is applied to demagnetize.
The magnetic coating was dried to form a magnetic layer by passing through a drying oven. Thereafter, it was calendered and cut into a predetermined width to produce a magnetic tape.

Example 2 The alternating current perpendicular magnetic field for demagnetization applied after orientation was applied at a frequency of 1.0.
A magnetic tape was produced in the same manner as in Example 1, except that the magnetic tape was 00 Hz, the perpendicular magnetic field strength was 2, and Oersted (Oe).

Comparative Example 1 Except for not demagnetizing by applying an alternating current perpendicular magnetic field,
A magnetic tape was produced in the same manner as in Example 1.

Comparative Example 2 The frequency of the AC perpendicular magnetic field for demagnetization applied after orientation was 60H.
A magnetic tape was produced in the same manner as in Example 1, except that the perpendicular magnetic field strength was Oersted (Oe).

Comparative Example 3 The magnetic paint was applied at a speed of 20 m/min, and spot drying was performed by blowing hot air (90°C) onto the coated surface from a nozzle in a vertically oriented magnetic field, and demagnetization was performed by applying an alternating current vertical magnetic field. A magnetic tape was produced in the same manner as in Example 1, except that the tape was tapered.

For each of the magnetic tapes produced in the above Examples and Comparative Examples, the squareness was measured as a magnetic property, and the surface smoothness of the magnetic layer was measured using a stylus type surface roughness meter using a center line average surface roughness (Ra value). ). These results are shown in the table below along with the manufacturing conditions.

From the results in the table above, the magnetic tapes (Examples 1 and 2) obtained by the manufacturing method of the present invention have a large square shape and a high degree of vertical orientation, have a high surface smoothness, and exhibit excellent electromagnetic conversion characteristics. That is clear.

On the other hand, the magnetic tape to which no alternating current perpendicular magnetic field was applied after vertical orientation (comparative example 1) and the magnetic tape in which the frequency of the alternating current perpendicular magnetic field was too low (comparative example 2) had small square shapes and significantly inferior orientation. It can be seen that the surface smoothness is also poor. In addition, with a magnetic tape using a conventional method (Comparative Example 3) in which the coating speed was slowed down and spot drying was performed in a vertically oriented magnetic field without applying an alternating perpendicular magnetic field, the orientation was almost good; It can be seen that surface roughness due to spot drying significantly deteriorates surface smoothness, resulting in poor electromagnetic conversion characteristics and, moreover, lowering productivity.

Claims (2)

[Claims] (1) Apply magnetic paint on a non-magnetic support, apply a magnetic field perpendicular to the coated surface to orient the magnetic particles, and then apply the magnetic paint to the coated surface while the magnetic coating is still wet. 1. A method for manufacturing a perpendicular magnetic recording medium, which comprises demagnetizing a magnetic coating film by applying an alternating current magnetic field with a frequency of 300 Hz or more having a magnetic field component in the perpendicular direction, and then drying it to form a magnetic layer. (2) The method for manufacturing a perpendicular magnetic recording medium according to claim (1), wherein the magnetic particles in the magnetic paint are hexagonal ferrite particles.