JPH03295028A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the medium having recording density exceeding conventionally by an application type magnetic recording medium by adding an application surface AC magnetic field being below its anti-magnetic force to needle-like or granular magnetic powder, and aligning the magnetic powder in the vertical direction of the application surface. CONSTITUTION:On a non-magnetic supporting body, a magnetic layer in which needle-like or granular magnetic powder and a resin compound binder are main agents is applied and formed. Subsequently, immediately thereafter, an in-application surface AC magnetic field in which the maximum magnetic field strength is below coercive force (Hc) of the magnetic powder is added so as to become the vertical direction to each other in two parts in the long size direction. It is limited to the in-surface vertical direction which can become the vertical direction in which the orientation focusing direction of the magnetic powder becomes the direction vertical to the applied AC magnetic field direction of two parts. In such a way, since no repulsion force is generated between adjacent magnetic particles, a vertical orientation processing of an application type medium whose surface is very smooth can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a coated magnetic recording medium used in video equipment, audio-related equipment, information-related equipment, and the like.

Conventional technology With the advancement of higher image quality in the field of video equipment, digital signal processing in the field of audio equipment, and miniaturization and faster processing of computer peripheral equipment, coated type external memory has been widely used. For magnetoelectric recording media, it has become important to improve recording and reproducing characteristics in high-density recording areas.

In the currently mainstream longitudinal magnetic recording system, there is a trend to employ metal magnetic powder with excellent magnetic properties as a recording element, and the following measures are being considered to increase the recording density.

■ Improve magnetic properties by making magnetic powder into fine particles and increasing the packing density of the particles in the magnetic layer.

■ Make the surface roughness of the magnetic layer as smooth as possible to suppress magnetic loss due to the gap between the magnetic layer and the magnetic head during recording and reproduction.

(2) In a tape that records in the longitudinal direction, the magnetic powder is aligned as much as possible in the longitudinal direction, which is the recording direction, to increase the residual magnetization strength of the magnetic properties.

However, in contrast to these efforts, ■ has limitations in creating ultrafine magnetic powder, and dispersion technology (dispersion material/dispersion processing method) to uniformly disperse ultrafine powder
There is also a problem above.

■The surface of the coated magnetic layer can be made mirror-like by ensuring and maintaining the surface properties of metal rolls for mirror-finishing, ensuring mechanical strength under high temperatures of elastic rolls for mirror-finishing, and binder properties that ensure mirror-finishing properties. There are limits to processing technology.

(2) There is a limit to the alignment processing technology that overcomes the interaction between ultrafine particles.

Due to the above-mentioned technical problems, it is difficult for coated magnetic recording media to secure the same high-frequency characteristics as those for media whose magnetic layer is a magnetic metal thin film formed by sputtering or vapor deposition.

On the other hand, among metal thin film media, it is already known that perpendicular magnetic recording media having an axis of easy magnetization in the perpendicular direction have excellent high-density recording characteristics. In the case of coated magnetic recording media, research and patent applications have been actively conducted year by year to provide the properties of perpendicular magnetic recording media by orienting acicular or granular magnetic powder in a direction perpendicular to the surface.

Problem to be Solved by the Invention In order to orient the axis of easy magnetization of the magnetic particles perpendicularly in a coated magnetic recording medium in which the magnetic particles are acicular or granular, a DC magnetic field is applied to the coating film immediately after coating in a direction perpendicular to the medium surface. The method is common.

However, this basic principle is based on the coercive force (Hc) of magnetic particles.
) By applying a magnetic field above, the magnetic moment is fixed to the axis of easy magnetization, and the magnetic particles begin to move and become oriented parallel to the external magnetic field. At this time, the magnetic moments between adjacent magnetic particles are oriented in the same direction, so a magnetic repulsion is generated, which is thermal. As the particle size becomes smaller, the interparticle distance decreases and becomes larger.

When vertically aligned based on such a principle, the magnetic particles escape from each other in the direction perpendicular to the coated surface due to mutual repulsion, resulting in surface roughness peculiar to this method.

Some of the above-mentioned applications describe methods for suppressing this surface roughness as much as possible, but no invention has been developed that fundamentally improves the surface roughness.

Perpendicular magnetic recording technology is characterized by the magnetization process of the recording signal, but its effectiveness is small if the gap between the recording and reproducing head becomes larger than that of a conventional longitudinal recording medium.

For this reason, with the medium obtained by the above-described invention, it has been difficult to actually realize recording and reproducing characteristics superior to those of ultra-smooth longitudinal magnetic recording media.

An object of the present invention is to solve the above-mentioned problems and provide a coated magnetic recording medium having a recording density higher than that of conventional media.

Means for Solving the Problems In the present invention, in order to achieve the above object, a magnetic layer consisting of acicular or granular magnetic powder and a resin binder is continuously coated on a non-magnetic support, and immediately after that, an external layer is formed. The maximum magnetic field strength is less than or equal to the coercive force (Hc) of the magnetic powder within the coating surface f
This method is characterized in that the magnetic powder is aligned in a direction perpendicular to the coated surface by an alignment process in which a magnetic field is applied at two locations in the longitudinal direction so that they are perpendicular to each other.

The principle of the present invention is that the magnetic moment of the magnetic powder causes an oscillating movement around the axis of easy magnetization by an alternating magnetic field whose maximum magnetic field intensity applied from the outside is less than the coercive force of the magnetic powder.

As a result of the amplitude movement of the magnetic moment, the magnetic powder gathers in the direction of the midpoint of the amplitude movement of the magnetic moment, ie, in a plane perpendicular to the direction of the applied magnetic field.

At this time, if the maximum magnetic field strength exceeds the coercive force, the magnetic field
K71''; [b angular'. Near 'axis of easy magnetization'. Fixed, and the behavior of the magnetic powder accompanying such amplitude motion cannot be obtained.

In the present invention, by applying an in-plane alternating current magnetic field whose maximum magnetic field strength is less than or equal to the coercive force of the magnetic powder so that the directions are perpendicular to each other at two long locations, the orientation and focusing direction of the magnetic powder is controlled. The direction is limited to an in-plane perpendicular direction which can be a direction perpendicular to the direction of the applied alternating magnetic field at two locations.

According to this basic principle, since no repulsive force is generated between adjacent magnetic particles, it is possible to vertically align a coated medium with a very smooth surface.

The specific method is to apply a current to two sets of AC electromagnets, I [''' IIIIX ' S l n (ωt), where l mmK is a current value such that the magnetic field generated by the electromagnets is less than or equal to the Hc of the magnetic powder. It is highly reliable even in continuous operation because the equipment itself does not have any moving parts, just by applying alternating current and arranging the magnetic fields generated by each magnet in directions perpendicular to each other. Furthermore, before applying an alternating current magnetic field from these two orthogonal directions, the initial orientation direction is set in the longitudinal direction by an in-plane longitudinal direct current magnetic field orientation treatment having a magnetic field strength three times or more than the coercive force of the magnetic powder. By arranging them, the effect of the rear two stages can be further enhanced to provide a coated vertical medium that is efficient and has excellent vertical alignment.

In this method, residual magnetization remains in the direction of the easy axis of magnetization by once applying a DC magnetic field of Hc or higher to the magnetic powder. However, due to the demagnetizing effect caused by the subsequent application of an alternating magnetic field, surface roughness due to repulsion between adjacent magnetic powders does not occur when the particles are oriented in a direction perpendicular to the surface. Rather, because the magnetic powder is initially oriented in the longitudinal direction, it can be more effectively oriented in the perpendicular direction than when alternating current magnetic fields from two orthogonal directions are directly applied.

EXAMPLE Hereinafter, a comparison between an example of the present invention and a conventional example will be explained with reference to the drawings.

Example 1 A specific configuration of an alignment apparatus based on the present invention will be described.

As shown in FIG. 1, the alignment processing apparatus used in this example is constituted by an electromagnet 1 having two sets of C-shaped cores. The electromagnet is composed of a C-shaped core 1-1 made of a ferromagnetic material with low magnetic permeability and a coil 1-2 made by winding a conductive wire with high conductivity. The electromagnets are arranged adjacent to each other in the longitudinal direction of the continuous medium 2, and the electromagnet at the front in the longitudinal direction is installed so that the magnetic poles at both ends of the letter 0 are lined up in the longitudinal direction.
The electromagnet at the rear in the longitudinal direction is installed so that its magnetic pole faces in the width direction. Then, an alternating current generator 3 applies a current of 1=laxx·s in (ωt) to each t stone. Here, I, . . . Also, by using a general single-phase 200cm AC, ω is 50cm.

By using such an orientation device, the present invention can easily orient the magnetic powder in the direction perpendicular to the coating surface without causing mutual magnetic repulsion.

Example 2 The configuration of the second embodiment is shown in the second section.

Embodiment 2 aims to make the principle of Embodiment 1 work even more effectively, and an in-plane long alignment device using a direct current magnetic field was installed on the front side in the longitudinal direction of the alignment processing device of Embodiment 1. It is something. The in-plane elongated orientation device consists of a set of rare earth permanent magnets (samarium cobalt) arranged with the same magnetic poles facing each other and sandwiching a elongated continuous medium.
5, and an electromagnet 5 wound in a solenoid shape with a conducting wire whose magnetic poles are set so as to absorb magnetic fields repelled by the same polarity. For the rare earth permanent magnet (samarium cobalt) that provides initial orientation, the magnetic field is set to three times the coercive force, and for the rear IIT magnet, the magnetic field strength is set to one to two times the coercive force.

Comparative Example In contrast to Examples 1 and 2 according to the present invention, orientation treatment according to the conventional method shown in Table 1 was examined as a comparative example.

Table 1 Ru.

In Comparative Example 1, in accordance with the conventional in-plane longitudinal recording method,
This is a device for orienting magnetic particles in the longitudinal direction of a continuous medium. Its configuration is shown in FIG.

This is composed of only the in-plane elongated orientation device used in Example 2, and 1&II rare earth permanent magnets (samarium cobalt) 4 arranged with the same magnetic poles facing each other and sandwiching a elongated continuous medium. , it is wound like a solenoid with a conductive wire whose magnetic poles are set so that it absorbs the magnetic field repelled by the same polarity! It is composed of a magnet 5.

Comparative Example 2 is an example of a vertical alignment method using a DC magnetic field.

Its structure, as shown in FIG. 4, consists of a set of rare earth permanent magnets (samarium cobalt) 6, with opposite poles facing each other with a long continuous medium in between, in order to generate a DC magnetic field.

However, this orientation method has the disadvantage that it is difficult to obtain the magnetic field length necessary to orient the magnetic powder on the elongated medium in the vertical direction.

Therefore, in Comparative Example 3, as shown in FIG. 5, four sets of rare earth permanent magnets are arranged in the longitudinal direction of the continuous medium in order to compensate for the drawbacks of Comparative Example 2.

In Comparative Examples 2 and 3, a DC magnetic field is obtained using a rare earth permanent magnet, but ■ The homogeneity of the magnetic field when magnetizing the permanent magnet ■ The influence of the magnetic field component returning from the magnetic pole that does not face the long medium The problem is that this greatly affects the deterioration of orientation.

Therefore, in Comparative Example 4, Comparative Example 2 was constructed using only a permanent magnet.
, 3, as shown in FIG. 6, two sets of t-magnets 7 are magnetically coupled by a yoke 8 made of ferromagnetic material to minimize the influence of magnetic fields from magnetic poles that do not face each other, and the magnetic poles are In the space between the two, a homogeneous DC magnetic field, which is a characteristic of TFM stones, can be obtained. The electromagnet used here is composed of a rod-shaped core 7-1 made of a ferromagnetic material with low magnetic permeability and a coil 7-2 made by winding a conductive wire with high conductivity.

Further, as shown in FIG. 7, Comparative Example 5 has a structure in which four sets of electromagnets used in Comparative Example 4 are arranged in a similar way to Comparative Example 3, which compensates for the drawbacks of Comparative Example 2.

Regarding Comparative Examples 2 to 5 introduced so far, considering the orientation principle, the magnetic field strength obtained with each configuration was set to three times the coercive force Hc of the magnetic powder. A polyethylene terephthalate film (hereinafter referred to as PET film) with a thickness of 10 μm was used as a nonmagnetic support, and a magnetic layer with a thickness of 3.0 μm was continuously coated on the surface thereof, and a hack coat layer with a thickness of 05 μm was formed on the back surface. A sample was made as a bi-band 811m VTR tape.

Hereinafter, the method for preparing samples for this example and comparative example will be explained in detail.

(1) Materials forming the magnetic layer The materials forming the magnetic layer and their ratios are: Metal magnetic material: 100 parts by weight Resin binder:
20 parts by weight Alumina 6 parts by weight Carbon 1 part by weight Aliphatic lubricant: 4 parts by weight Hardening agent
4 parts by weight.

Metal magnetic material is for bi-band 8m VTR (!
: We selected the ones that are widely known and easily available for boat fishing. Table 2 shows the characteristics.

The resin binder in Table 2 is mixed with the resin shown in Table 3.
It has a standard configuration as a binder for tapes.

(Left below) Blend ratio: Weight ratio based on the weight of magnetic powder in 100 The amount of each is determined as the best ratio based on the results of a tensile test of a coating film with a binder resin system and a scratch strength test of a magnetic coating film. There is.

Resin d was chosen to pretreat alumina.

Alumina has a particle size of 0.10-0.30 am
A common material having a specific surface area of 9 to 15 m''/H was used, and 1 part by weight of resin d was dispersed in advance at an appropriate viscosity using a mill disperser.

For the remaining 19 parts by weight of binder, mix the magnetic powder
It was added during pre-dispersion. Regarding carbon, carbon having a secondary particle size of 200 to 300 particles was used.

Three types of aliphatic lubricants commonly used in magnetic recording media were selected and mixed in the following blending ratio.

C11: 2 parts by weight C: 1 part by weight C-C: 1 part by weight II A commonly used isocyanate compound was used as the curing agent.

(2) Creation of magnetic paint The magnetic paint was prepared as follows.

After adding the metal magnetic powder, carbon, and fR mixture of methyl ethylkene and toluene anone in a ratio of 3:3:1 to a mixer and stirring for one hour to sufficiently wet the powder with the solvent, resin a. While adding Resin B, Resin C and the remaining amount of the mixed solvent to a mixer, the mixture was stirred for 5 hours to increase the powder size. Thereafter, the mixture was kneaded for 4 hours without adjusting the viscosity of the coating material.

After diluting this magnetic kneaded material, it was dispersed using a sand mill, which is commonly used for dispersing paints. Upon completion of the sand mill secondary dispersion, alumina paste which had been separately dispersed using resin d was added and extracted, and the secondary dispersion treatment was performed again using the sand mill.

Immediately before coating, a lubricant solution and a curing agent were added and stirred to the metal magnetic paint stock solution obtained in this manner to complete the preparation of the magnetic paint.

(3) Formation method of magnetic layer The method of forming the magnetic layer is to continuously coat the prepared and dispersed magnetic paint onto the PET film using a gravure coater, and immediately after coating, as described in Example 1 of the present invention. 2 and Comparative Examples 1 to 5 were subjected to orientation treatment using a conventional method. After the orientation treatment, a suitable amount of warm air was blown through a nozzle to prevent the magnetic powder from returning to its orientation, and the orientation was fixed to the extent that surface roughness due to rapid drying of the coating film was not caused. Thereafter, after passing through a main drying step, a calender treatment was performed to give a mirror finish, and this was subjected to a curing reaction in a curing furnace.

(4) Method of forming a back coat layer.

After forming and curing the magnetic layer, the back coat layer was formed by continuously applying a special paint containing carbon paint as a main component using a gravure coater.

After slitting each of the samples thus prepared into eight widths, their characteristics were compared and examined. For convenience of explanation, numbers are given as shown in Table 4.

For each sample in Tables 4 and above 1-1.1-2.2-1 to 2-5, ■ In-plane longitudinal component, width direction component, and surface perpendicular component of tape squareness ratio (Br/8m) ■ Surface of magnetic layer Roughness■ We evaluated the frequency characteristics of the recording/playback output. When evaluating each, ■
Vibrating magnetization measuring device ■ Optical interference type non-contact three-dimensional surface roughness meter ■ A commercially available Biband 8 ■ A modified electric VTR was used.

The evaluation results will be explained step by step below.

Figure 8 shows the squareness ratio in the tape length direction/width direction and the perpendicular direction for each sample of ]-]1.1-2.2-1 to 2-. This was measured using a type magnetization measuring device. For the direction perpendicular to the plane, a value is used which is corrected by 4πMs for the influence of the demagnetizing field resulting from the film thickness effect. As is clear from FIG. 8, sample 1-1.1-22- was subjected to vertical alignment treatment.
Sample 1-2 according to the present invention among the six samples 2 to 2-5
The squareness ratio indicating the magnetization component in the direction perpendicular to the plane is the highest, and the squareness ratio in the longitudinal direction is also the smallest. That is, the orientation state of the magnetic powder has almost no in-plane component and is efficiently oriented in the direction perpendicular to the plane. Sample 1-1 has the second highest perpendicular magnetization component. It can be seen that the squareness ratios of Sample 1-1 in the tape longitudinal direction and width direction are approximately the same value, and that the in-plane component is isotropic. Conventional sample 2-
In 4.2-5, since the surface perpendicular squareness ratio and the longitudinal squareness ratio are high and the width direction component is small, even though it is oriented perpendicularly by the DC magnetic field, it is dragged by the magnetic field without being completely oriented, and as a result, the longitudinal This shows that the ingredients are increasing. In sample 2-22-3, among the three orientation components, the vertical direction is high, but the other two components are also large, and the vertical component is only slightly stronger than the random orientation direction of the magnetic powder. do not have.

In Figure 9 (al-(g), l-1, 1-2, 2-1
The measurement results of the three-dimensional surface roughness of each sample of -2-5 are shown. 2-2-2 aligned by a DC magnetic field perpendicular to the plane
Each of the samples No.-5 had significantly poorer surface properties than No. 2-1, which is a conventional tape example which was first oriented in the in-plane longitudinal direction. This is because magnetic powders with magnetization caused magnetic aggregation with each other due to a DC magnetic field three times stronger than Hc, and the extent of this was even worse in sample #4, which had a large magnetization component in the direction perpendicular to the surface. I understand. On the other hand, sample 1-1.1-2 according to the present invention achieves the same level of surface properties as conventional tape 2-1, although the magnetization component in the direction perpendicular to the surface is the largest. In particular, the fact that there is no large difference between samples 1-1 and 1-2 indicates that the demagnetizing effect due to the alternating magnetic field described in the section of the effect appears in sample 1-2.

As is clear from this result, sample 1-
1.1-2 is sample 2- which was subjected to vertical alignment treatment in the comparative example.
The surface properties, which were difficult to achieve with 2 to 2-5, are compatible with the squareness ratio in the direction perpendicular to the surface, while achieving high levels of both.

Regarding Sample 1-1.1-2 and Conventional Tape Example 2-1, which have surface properties at a practical level, commercially available Biband 8 +w
A VTR deck was modified and the frequency characteristics during recording and playback were measured. FIG. 10 shows the results.

In particular, it shows a higher output than conventional tapes in the high frequency range, and it is clearly seen that the characteristics of the perpendicular magnetization film, which is the object of the present invention, can be realized with coated magnetic tapes.

In the embodiments described above, a copper flat wire is coiled around a ferromagnetic core and used as an Nfet stone, but this does not define the structure of the present invention. In order to suppress the heat generated by the electromagnet during long-term energization, a cooling pipe may be incorporated or a hollow low-resistance conductor wire may be used for the coil. Furthermore, a superconducting magnet applying the superconducting phenomenon may be used so that the magnetic field specified by the present invention can be obtained when the distance between the magnetic poles is increased.

Further, in each of the embodiments, the orientation device has one electromagnet and applies an alternating current magnetic field in one direction, but this does not limit the present invention. Due to the relationship between the size of the equipment, the line speed, and the magnetic field length required to obtain the effect, a plurality of 1i magnets of a realistic size may be used to perform this function.

Further, although a bi-band 8 m VTR tape has been described as an example of producing a coated magnetic recording medium according to the present invention, the present invention can also be applied to other VTR tapes, 5 magnetic tapes, or magnetic disks such as flexible disks.

Effects of the Invention As is clear from the above embodiments, the present invention provides a coated perpendicular magnetic recording medium that achieves an ultra-smooth surface without impairing the surface properties of the magnetic layer and has excellent coated surface direct alignment properties. It can be produced continuously and stably. And of the medium obtained by the present invention! The magnetic conversion characteristics exhibit excellent recording and reproducing characteristics even in high-density recording areas.

[Brief explanation of the drawing]

1(a) and 1(b) are schematic plan views and front views showing an example of a magnetic field orientation device used in carrying out the present invention, and FIG. 2 is a schematic plan view and front view showing an example of a magnetic field orientation device used in another embodiment of the present invention. A schematic front view, FIG. 3 is a schematic configuration diagram of an orientation apparatus for manufacturing a conventional magnetic tape oriented in the longitudinal direction as a comparative example, and FIGS. A schematic diagram showing the orientation method in the comparative example given in
FIG. 8 is a characteristic diagram summarizing the results of measuring the squareness ratio in the tape longitudinal direction, width direction, and surface perpendicular direction using a vibrating magnetization measuring device for each of the samples of Examples and Comparative Examples that were actually produced as prototypes. Figures (a) to (g) show the results of surface roughness measurements using a non-contact three-dimensional surface roughness meter. FIG. 3 is a characteristic diagram showing the results of comparing the frequency characteristics of the conventional tape in the present example and the comparative example, in which the characteristics were obtained, using a commercially available Vivant' 8 an VTR deck. 1...Electromagnet with 0-shaped core, 1-1...
0-shaped core, 1-2... Coil by conductor, 2.
... Long continuous medium, 3 ... Alternating current; flow generator.

Claims (2)

[Claims] (1) A magnetic layer mainly composed of acicular or granular magnetic powder and a resin binder is coated on a non-magnetic support, and immediately thereafter applied from the outside so that the maximum magnetic field strength is less than the coercive force (Hc) of the magnetic powder. A method for manufacturing a magnetic recording medium, which comprises aligning magnetic powder in a direction perpendicular to a coated surface by applying an in-plane alternating current magnetic field at two locations in a longitudinal direction so as to be perpendicular to each other. (2) A magnetic layer containing acicular or granular magnetic powder and a resin binder as main ingredients is coated and formed on a non-magnetic support, and immediately thereafter an orientation treatment is performed by applying an external magnetic field at three locations in the longitudinal direction. The first stage uses a direct current magnetic field orientation treatment in the in-plane longitudinal direction, which has a strength more than three times the coercive force of the magnetic powder.
After that, the magnetic powder is aligned in the direction perpendicular to the coated surface through an alignment process in which an alternating magnetic field within the coated surface with a maximum magnetic field strength equal to or less than the coercive force (Hc) of the magnetic powder is applied at two locations so that they are perpendicular to each other. A method for manufacturing a magnetic recording medium.