JPH0489624A - Production of perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the perpendicular magnetic recording medium having a magnetic layer which has a high degree of perpendicular orientability and has a smooth surface by providing a plane heating body which does not hinder the magnetic fields between magnetic poles of different poles facing each other along an object to be treated and transmitting heat to an undried coating layer by this heating body. CONSTITUTION:The PET film 19 formed with the undried coating layer 20 is introduced to a perpendicular orienting device 11 and is passed in the orienting magnetic fields of 3000G by bringing the rear surface of the PET film into contact or proximity to the 'Teflon(R)' surface of the iron plate 14. A heater 16 is previously operated at this time and is so set that the surface temp. of the 'Teflon(R)' of the iron plate 14 attains about 60 deg.C. The magnetic material particles in the coating layer in the undried state is then perpendicular ly oriented and the heat is transmitted from the 'Teflon(R)b surface via the PET film 19 to the undried coating layer, by which the solvent of the coating material of the coating layer is evaporated and the coating layer is dried. The magnetic characteristics in the perpendicular direction are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a coated magnetic recording medium using a perpendicular magnetic recording method.

[Conventional technology]

In recent years, there has been a desire to develop high-density magnetic recording media that are excellent in recording and reproducing at short wavelengths. From this point of view, the conventionally commonly used recording method is to magnetize a magnetic recording medium having a magnetic layer with magnetic particles oriented in the longitudinal direction of the magnetic tape parallel to the surface of the magnetic layer using a ring head. Since there is a theoretical limit to increasing the packing density of the magnetic material in the magnetic layer, it is disadvantageous for use in high-density recording.

Therefore, as a high-density type magnetic recording medium, a so-called perpendicular magnetic recording method, that is, a perpendicular magnetic recording medium having a magnetic layer in which the axis of easy magnetization of magnetic particles is oriented perpendicularly, is used. The method of recording by magnetization has attracted attention, and its perpendicular magnetic recording media are being actively researched. This perpendicular magnetic recording method not only allows magnetic particles to be packed in the magnetic layer at a high density, but also has little influence from demagnetizing fields, so it is possible to use an SPT head instead of a ring head, and in principle it is short. It has been confirmed that it has excellent recording and reproducing characteristics at various wavelengths and is suitable for high-density recording.

This perpendicular magnetic recording medium is produced by forming a thin film of a ferromagnetic metal such as a Go-Cr alloy on a base film such as a polyethylene terephthalate film (PUT film) by sputtering or vapor deposition to form a recording layer. is being studied. However, the metal thin film recording layer formed by these methods not only has problems with running durability and corrosion resistance when rubbed by a magnetic head when used as a magnetic recording medium, but also has problems with running durability and corrosion resistance when rubbed by a magnetic head when used as a magnetic recording medium. There is also a problem in terms of production efficiency.

Therefore, a coated perpendicular magnetic recording system that can be produced by a so-called coating method has fewer of these problems, has excellent flexibility in the magnetic layer, is easy to operate, and can make use of years of research into magnetic recording media. Creating a medium is being studied. As this coating type magnetic recording medium, for example, hexagonal plate-shaped barium ferrite (BaFe1
20+5) A magnetic paint made by dispersing powder or acicular iron oxide powder in an organic binder, etc. is applied to the base film, and before the paint film dries, a magnetic field is applied in the perpendicular direction of the coated layer to coat the axis of easy magnetization. A method of vertically aligning the layers is being considered.

Among these, magnetic recording media using hexagonal plate-shaped hali-rham ferrite powder as a magnetic material have a low saturation magnetic flux density (Bs), so there is a risk of insufficient output in the low frequency range.

On the other hand, when producing a coating-type perpendicular magnetic recording medium using acicular magnetic powder, which produces a coercive force Hc due to shape anisotropy, as a magnetic material, there is a problem that the surface of the magnetic layer becomes rough. In this respect, if it is a type of magnetic tape that records by magnetizing magnetic particles parallel to the magnetic layer, such as a magnetic tape that has a magnetic layer in which magnetic particles are oriented in the longitudinal direction, as shown in Figure 2 (a). As shown in the figure, the easy magnetization axes, that is, the long axes of the magnetic substances 3. When the magnetic particles are passed through the PUT film on which the coating layer has been formed, the magnetic particles are arranged parallel to the undried coating layer, and the surface of the coating layer does not become rough, causing no problem.

However, in the case of coated perpendicular magnetic recording media, the second
As shown in Figure (b), it is necessary to form a coating layer 6 with the long axis of the magnetic material 3. Vertical alignment processing methods, direct current alignment processing methods, etc. are employed.

Specifically, a well-known method is to apply a magnetic field perpendicularly to the undried coating layer through a pair of magnets of different polarities facing each other, for example, a PET film on which the undried coating layer has been formed.

[Problem to be solved by the invention]

However, in order to efficiently make a long axis of an acicular magnetic material such as 1-Fe2O3 perpendicular to obtain a magnetic layer with enhanced vertical orientation, the coercive force Hc of the magnetic material caused by shape anisotropy must be Since a sufficiently large magnetic field is applied perpendicularly to the wet coating layer, the strength and direction of the magnetic field between the opposing magnets is not the same between the edge portions and the center portion of the magnets. The orientation is disturbed by the magnetic field, and the surface layer of the coating layer rises in the direction of the applied magnetic field due to magnetic aggregation, resulting in not only a low degree of perpendicular orientation but also
There is a problem in that unevenness occurs on the surface of the coating layer, causing the surface to become rough, ie, so-called surface deterioration.

In addition, as shown in FIG. 3, the acicular magnetic particles 6.6 of the undried coating layer 5 in the air-dried state have different polarity magnets 7a,
Even if it is oriented vertically when passing between 7b and 7b, it will rotate or fall back in an attempt to return to its original position when it is no longer affected by the applied magnetic field, resulting in the so-called "return" phenomenon, and the more the needle-like shape There is also the problem that the degree of vertical orientation of the magnetic particles decreases.

Regarding these problems, A, Oh tube,
Y.

5atoh, T., Masuko, T., Watanab
e, IEEE Trans, MAG-233149 (1
987) and Yuji Sato, Akio Otsubo, and Hikoyoshi Momoi.

Toshio Kobayashi, 13th Japanese Society of Applied Magnetics, Academic Lecture Summary 22
A4 (1987).

When a magnetic layer consisting of a coated layer with so-called surface deterioration as described above is used, for example, as a magnetic recording network tape, the distance between the magnetic head and the tape will vary, resulting in so-called spacing loss, and the playback output will be affected. This may lead to a decrease in This is a big problem, especially for magnetic recording media that record images in a short wavelength range.

Therefore, in order to solve these problems, a LIPS alignment device as shown in FIG. 4 has been proposed (for example, Y,
5atoh, A., 0htubo, T., Masuko, M.
, Kurematsu.

IEEE Trans, MAG-23, 3149 (19
88)). That is, a plurality of sets of magnets each having a pair of N and S poles facing each other are provided, and the N and S poles are arranged in reverse for every set of magnets, so that the surface layer of the magnetic coating layer is perpendicularly magnetically oriented, and the deep layer is magnetically oriented longitudinally. Magnetic tapes having layers have been proposed. In addition, 8
9 is a coating device, and 9 is a base film on which an undried coating layer is formed after the coating device.

However, even this method cannot be said to have solved the above problems. Among the above-mentioned problems, in particular, the phenomenon of "return" explained based on Fig. 4 is caused by: ■ The magnetic particles tend to fall down due to insufficient drying of the coating layer; Causes include disruption of arrangement due to the influence of demagnetizing fields between body particles. In this case, if the drying process is too good in an attempt to eliminate the cause of (2), the coating layer will harden before the magnetic particles are oriented, and not only will the degree of orientation of the particles in the resulting magnetic layer become low. This causes a problem in that the surface of the magnetic layer tends to become rough.

Therefore, in order to reduce the "one return" of magnetic particles, it is important to select a drying method during magnetic field orientation.

Regarding this drying method, please refer to the above Y, 5atoh, A, 0
htub.

, T., Masuko, M., kurematsu, I.E.
EE Trans, MAG-23, 3149 (198B
) proposes a method using A11l [1IIY (air drying) or a combination of this and infrared irradiation.

According to this method, by changing the amount of air drying and the amount of infrared rays irradiated, it is thought that vertically oriented particles in the coating layer are fixed as the paint dries from the surface layer to the deeper layers. The magnetic tape obtained after calendering as a post-processing has a tape squareness ratio Br10s in the vertical direction as high as 0.66 (with demagnetizing field correction).

Note that the strength of the orientation magnetic field at this time is about 2 KOe, and even if it is made stronger than this, this Br/Bs will hardly change.

However, even if the magnetic particles in the wet coated layer subjected to magnetic field orientation treatment are vertically oriented, when the wet coated layer on the running base film is out of the influence of the magnetic field, the magnetic particles If there is a degree of freedom of movement, "return" occurs as described above. Furthermore, even if air-drying or infrared rays are used to dry an undried coating layer, especially when sprayed or irradiated from the coating layer side, the coating layer is dried and cured sequentially from the surface to the deep layers, and the deep layers are Since the magnetic particles in the deep part have a high degree of freedom of movement, when they are no longer affected by the orienting magnetic field, the deep part will move freely.
"Return" also becomes larger. In addition, it is difficult to make the amount of air blown and the amount of infrared rays uniform throughout the undried coating layer on the moving base film, and the degree of dryness and curing of the coating layer may vary depending on the location. Therefore, there is also a problem that the degree of orientation of the magnetic particles also differs depending on the location.

An object of the present invention is to provide a method for manufacturing a coating-type perpendicular magnetic recording medium, which has a magnetic layer with a smooth surface and a high degree of perpendicular orientation obtained by reducing the "return" of magnetic particles after orientation in a magnetic field. The objective is to obtain a perpendicular magnetic recording medium.

[Failure to solve the problem]

In order to solve the above-mentioned problems, the present invention aims to provide an easy-to-magnetize axis of magnetic particles by passing an object to be treated, which has a wet coated layer of magnetic paint on a non-magnetic support, between opposing magnetic poles of different polarities. In the manufacturing method of a perpendicular magnetic recording medium, the method includes a vertical alignment treatment step of orienting the applied layer perpendicularly to the principal surface of the coated layer, in which the object to be processed is placed in a magnetic field between the opposing magnetic poles of different polarities without interfering with the magnetic field. The present invention provides a method for producing a perpendicular magnetic recording medium, characterized in that a flat heating body is provided along the vertical axis, and heat is transferred to the undried coating layer by the heating body.

At this time, the object to be processed that has been heated by the heating element is rapidly cooled down. The non-magnetic support on the back surface should be in contact with this heating element to transfer heat, the quenching treatment should be carried out by bringing the object to be processed into contact with the cooled metal plate, and the longitudinal direction of the coating layer should be applied before the vertical alignment process. It is also preferable to orient the magnetic particles.

[Effect]

When the object to be treated is heated with a flat heating element, heat is uniformly transferred to the undried coating layer, and if this heat transfer is performed from the non-magnetic support side on the back side of the object to be treated, the undried coating layer is heated from within. be done. Heating in this way accelerates drying and
The curing of the resin in the coating layer is accelerated. Therefore, vertically oriented magnetic particles have less freedom of movement,
This is promoted by rapid cooling, especially for the internal particles, and finally the orientation state of the magnetic particles is fixed.

〔Example〕

Next, the present invention will be explained in detail.

Example 1 FIG. 1 shows a part of the manufacturing process of the magnetic recording medium of the present invention, in which 11 is a vertical alignment processing device, and 12 is a quenching device.

The vertical alignment processing device 11 has permanent magnets 13a, 13b, 13c, 13d on the bottom surface of a perforated wooden board 12, and permanent magnets 15a, 15b, 15c on the bottom surface of an iron plate 14 with a thickness of about 5 m, which is made by pasting the N pole on the bottom side. , 15d are fixed with their S poles facing upward, corresponding to the permanent magnets, and a heater 16 made of nichrome wire is arranged on the lower surface of the iron plate 14 around these magnets. Note that 16a is an explosion-proof cover. A non-magnetic support on which an undried coating layer (described later) has been formed passes between these upper and lower structures, but these structures are tilted upward to prevent evaporated paint vapor from being trapped. ing.

The surface magnetic flux density of the above permanent magnet is 3000G (Gauss)
It is preferable to use a moderately magnetized Fe-5m-Co magnet or a Fe-Nd-8 magnet having stronger magnetic energy.

In addition, the quenching device 12 includes a flat hollow body 16' made of iron, which is inclined so that its flat upper surface is parallel to the running surface of the PUT film on which a coating layer (to be described later) is formed and is upwardly tilted. A pipe 17 is connected to the front and rear center of the flat hollow body, and a circulation pump 18 is connected to this pipe.
A coolant such as water is circulated to cool the flat hollow body 16'. By providing the flat hollow body at an angle in this way, it is possible to prevent the evaporated solvent of the undried coating layer from being trapped.

Note that the surface of the iron plate may be covered with a Teflon sheet.

To produce a magnetic tape using the above-mentioned apparatus, a magnetic paint having the following composition is applied to the surface of a PET film 19 as a non-magnetic support using a coater (not shown) to form an undried coating layer 20.

Acicular alloy powder 100M parts Vinyl chloride resin 8M parts Urethane resin
12 parts by weight polyisocyanate
6 parts by weight Myristic acid 3 parts by weight n-butyl stearate 1 part by weight Toluene 130 parts by weight Methyl ethyl ketone 130 parts by weight Abrasive (granular α-A”2
05) 12 parts by weight The acicular alloy powder used had a long axis of 0.2 μm, a short axis of 0.03 μm, a specific surface area (BET value) of 52 g7 g, and a coercive force Hc of 900 δe.

Further, the coating conditions are as follows.

Coater: Direct gravure coating speed:
Coating thickness: 4.0 μm (dry coating) PUT film thickness: 14 μm Next, the PET film 19 on which the undried coating layer 20 was formed was passed through the guide roller 21 to the vertical orientation device. 11, and passed through an orientation magnetic field of 3000 G with the back side of the PET film in contact with or close to the Teflon surface of the iron plate 14. At this time, the heater 16 is operated in advance and the iron plate 1 is heated.
Set the surface temperature of the Teflon in Step 4 to approximately 60°C.

By doing this, the magnetic particles in the undried coating layer are vertically oriented, and heat is transferred from the Teflon surface to the undried coating layer via the PUT film 19.
The solvent of the paint in the coating layer is evaporated and the coating layer is dried. This evaporation of the solvent is continued while the undried coating layer is under the action of the orienting magnetic field, so that the coating layer is substantially dried.

During this time, the resin is accelerated to harden.

The PET film 19 with this almost dry coating layer is led to the quenching device 12, and water is circulated in advance to reduce the temperature.
A PET film 1 is placed on the upper surface of the flat hollow body 16' set at ℃.
9. Touch the back sides.

As a result, the coating layer is rapidly cooled and hardened, and the vertically oriented magnetic particles lose their degree of freedom and are fixed to the bangu resin, thereby suppressing "return". The PET film 19 having the coating layer subjected to the vertical alignment treatment is sent to the dryer 22, where the resin of the coating layer is further accelerated to harden. At this time, the magnetic particles are fixed to the resin and will not "return".

The object dried in this way is wound up and made into a PET
An original magnetic tape having a magnetic layer on the film is completed.

The above original magnetic tape was polished to a mirror finish and cut to create a magnetic tape having a magnetic layer with a dry coating thickness of 4 μm.To examine the degree of orientation in the perpendicular direction, the coercive force and squareness were compared (both in the perpendicular direction). The magnetic properties were measured using a sample vibrating magnetic flux needle (manufactured by Riken Denshi Co., Ltd.).

These results are shown in the table. The larger these values, the higher the degree of vertical orientation. Furthermore, the surface roughness (surface roughness, that is, the root mean square value of unevenness) of the magnetic layer of the magnetic tape was examined using a surface roughness meter.

The results are shown in the table. Note that the surface roughness of commercially available VTR tapes is 0.015 to 0.025 μl.

Example 2 In Example 1, the temperature of the Teflon surface of the iron plate 14 was set to 6
0°C, and the surface temperature of the flat hollow body 16' is about 2°C.
A magnetic tape was made in the same manner except that it was maintained at 5°C.
This was also measured in the same manner as in Example 1, and the results are shown in the table.

Example 3 A magnetic tape was produced in the same manner as in Example 1, except that the PET film was processed with the vertical alignment processing device II while it was stopped, and then the processing with the quenching device 12 was not performed. The results measured in the same manner as in Example 1 are shown in the table.

Comparative Example 1 In Example 1, the iron plate 14 was not heated during the treatment in the vertical alignment processing device 11, but was kept at room temperature (25° C.), and air was blown from between each of the magnets 15 to 18 attached to the perforated wooden plate 12. At the same time, the surface temperature of the flat hollow body 16' of the quenching device 12 is brought to room temperature (25°C) by irradiating infrared rays.
A magnetic tape was prepared in the same manner except that it was held at The running speed of the PET film is 6 m/min, 8 m/min,
The drying conditions were optimized by performing three types of drying at 10 m/min.

These magnetic tapes are also 1jl1 as in Example 1.
The results obtained are shown in the table.

Comparative Example 2 In Example 3, the iron plate 14 was not heated during the treatment in the vertical alignment processing device 11, but kept at room temperature (25°C), and air was blown between each of the magnets 15 to 18 attached to the perforated wooden plate 12. A magnetic tape was prepared in the same manner as in Example 1, except that infrared rays were irradiated, and the results are shown in the table.

(Margins below this page) Note that the squareness ratio is a value corrected by demagnetizing field.

From the above results, it can be seen that the method of Example 1.2 in which the magnetic tape material is created while running the PUT film has superior magnetic properties and coating speed compared to Comparative Example 1 in which the magnetic tape material is created in the same manner. It is about the same as that of Example 3, which has a low value. In addition, in the magnetic tape of Example 3, the running of the PUT film was stopped and the coating layer was dried and cured in an orientation magnetic field, so there is almost no "return" after orientation of the magnetic particles. Depending on the strength of the magnetic field and magnetic particles, not only iron plates but also ferromagnetic metal plates can be used, plates made of materials with good geothermal conductivity can also be used, and planar heating elements can also be used. Also, metal, ceramic, plastic, etc. can be used as the material for the perforated wooden board.

Further, as the acicular alloy powder, Fe-Ni, Fe-
Although alloys such as NiC0 can be used, instead of this acicular alloy powder, r-Fe2J, Co-containing ]-Fe205,
Oxides such as CrO2, iron nitride, iron carbide, etc. can also be used.

Further, although PUT film is used as the non-magnetic support in the above example, the present invention is not limited to this, and it is also possible to use a PUT film provided with an undercoat layer and a back coat layer.

〔Effect of the invention〕

According to the present invention, during the vertical alignment treatment in which the axis of easy magnetization of the magnetic material in the wet coated layer of magnetic paint is aligned perpendicularly to the coated layer, a flat heating body, such as a ferromagnetic metal plate, is heated. By heating the coated layer using heat, it is possible to uniformly dry the undried coated layer and uniformly accelerate the curing of the resin. The number of particle returns can be reduced. At this time, it is thought that the degree of perpendicular orientation closest to the limit can be obtained from the relationship of continuous coercive force. Comparative Example 2 uses a conventional drying method for vertically aligning the magnetic particles in the coating layer, but P
Since the running of the ET film was stopped, the drying was improved and the magnetic properties were clearly expressed.

In the above example, only vertical alignment treatment was performed, but
If the magnetic particles are first aligned in the longitudinal direction of the undried coating layer and then vertically aligned, the alignment efficiency can be increased.

In the above, the distance between the opposing magnets of different polarities may be within a range that allows disturbance of the vertical orientation of the magnetic particles, and may be determined as appropriate along with the magnetic field strength of the magnets. These magnets can also be used opposite each other with different vertical pressures.

In the above embodiment, the iron plate 1 is
4 was installed and the temperature was set at 60℃, but this temperature was 60-8
Although it is preferable to keep the temperature constant at 0°C, it is also possible to make the inlet low and the outlet high to reduce drying at first to make it easier for the particles in the undried coating layer to move. By scattering and rapidly cooling, this "recovery" phenomenon can be further reduced. In this way,
It is possible to provide a magnetic recording medium having a magnetic layer with a high degree of perpendicular orientation and less disturbance on the surface, and with less surface roughness.

In this way, it is possible to provide a magnetic recording medium that has magnetic properties whose recording wavelength extends to an extremely short wavelength range and is suitable for perpendicular magnetic recording.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a part of the apparatus used in the manufacturing method of one embodiment of the present invention, and Fig. 2 (a) is an explanatory diagram when magnetic particles are oriented parallel to the main surface of the coating layer. , The same figure (b) is an explanatory diagram when magnetic particles are oriented perpendicularly to the main surface of the coating layer,
FIG. 3 is a cross-sectional explanatory view of "return" that occurs during vertical alignment processing, and FIG. 4 is a schematic explanatory view of a conventional apparatus. In the figure, 11 is a vertical alignment device, 12 is a quenching device, 13a-
13d, 15a to 15d2 are magnets, 14 is an iron plate, and 16 is a nichrome wire.

Claims (5)

[Claims] (1) The object to be treated, on which a wet coated layer of magnetic paint is formed on a non-magnetic support, is passed between opposing magnetic poles of different polarities so that the axis of easy magnetization of the magnetic particles is perpendicular to the main surface of the coated layer. In the manufacturing method of a perpendicular magnetic recording medium, which includes a perpendicular alignment treatment step to orient the object, a flat heating body is provided in the magnetic field between the opposing magnetic poles of different polarities without interfering with the magnetic field and along the object to be processed. A method for manufacturing a perpendicular magnetic recording medium, characterized in that a heating element is provided to transfer heat to the undried coating layer. (2) The method for manufacturing a perpendicular magnetic recording medium according to claim 1, characterized in that the object to be processed heated by the heating body is rapidly cooled. (3) The heating body is made of a heated ferromagnetic metal plate and is placed in contact with the magnetic pole located on the back side of the non-magnetic support, and the non-magnetic support on the back side of the object to be processed is in contact with this heating body. 3. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the heat is transferred by using a perpendicular magnetic recording medium. (4) The method for manufacturing a perpendicular magnetic recording medium according to claim 1 or 2, wherein the quenching treatment is performed by bringing the object to be processed into contact with a cooled metal plate. (5) Claim 1 characterized in that a treatment for orienting the magnetic particles in the longitudinal direction of the coating layer is performed before the vertical alignment treatment step.
4. The method for manufacturing a magnetic recording medium according to any one of 4 to 4.