JPS59229746A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the surface smoothness of a magnetic layer and to reduce the variance of output level by leading a base film into and out a magnetic field formed by revolving a magnetic field generating means or shifting endlessly in locus said means with revolution so that the magnets of the same polarity are set opposite to each other in the vertical direction. CONSTITUTION:Roll magnets 7 and 8 for orientation are revolved at the same speed in the directions shown by arrows A and B. Many magnets 71 and 81 are set so that the same polarities are always set opposite to each other on the basis of a base film 2. As a result, a magnetic field parallel to the lengthwise direction of the film 2 and another magnetic field parallel to the width direction of the film 2 and another magnetic field parallel to the width direction of the film 2 are applied repetitively at any position of a coated film 6 on the film 2 and within the surface of the film 6. Then the orientating direction is corrected to the magnetic powder particles orientated in the lengthwise direction of the film 2 while a magnetic coating material is applied. As a result, the magnetic powder particles in the film 6 have no orientation, and the square forms are almost equal to each other between the lengthwise and width directions. Such a film is dried up and then blanked into a circular shape to obtain a magnetic disk. Thus a considerable variance of the output level is eliminated with this magnetic disk when the record/reproduction is carried out in the circumference direction of the disk. In such a way, the electromagnetic conversion characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium. The present invention relates to a method of manufacturing a highly reliable magnetic recording medium such as a magnetic disk that has little fluctuation in output level and has no oscillation.

Generally, a magnetic disk is made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, drying it to form a single magnetic layer, and then punching this out into a circular shape. In such magnetic recording media, since magnetic recording is performed in the circumferential direction, it is preferable that the acicular magnetic powder particles in the magnetic layer have no directionality and are non-oriented.

For this reason, in conventional magnetic disks, it is difficult to make the acicular magnetic powder contained in the magnetic layer non-oriented by applying magnetic paint onto the base film and then drying it without applying any magnetic field orientation. However, although this method can make the acicular magnetic powder almost non-oriented, the shearing force applied to the magnetic paint during application of the magnetic paint causes the magnetic powder particles in the magnetic layer to move slightly in the longitudinal direction of the base film. It is difficult to prevent the magnetic powder particles in the magnetic layer from being oriented in a sufficiently non-oriented manner. Therefore, attempts have been made to reduce the orientation of the magnetic powder particles as much as possible when applying the magnetic paint by lowering the viscosity of the magnetic paint, but this method can effectively make the magnetic powder particles non-oriented. On the other hand, as in the case of using highly viscous magnetic paint, the surface smoothness of the magnetic layer is not sufficiently good, making it difficult to sufficiently improve the recording density of magnetic disks, which have recently become increasingly dense. Can not.

As a result of intensive studies to overcome this problem, the inventor of the present invention painted a magnetic paint on a base film, and then sandwiched the base film and placed the magnets above and below each other, so that each magnet was independent and compatible with the others. The magnetic field generating means is formed by arranging a plurality of magnets such that adjacent magnets have different polarities, and the magnetic field generating means is rotated or rotated in an endless orbit so that the magnets of the same polarity face each other in the vertical direction. When introduced into a magnetic field formed by
Even if the magnetic powder particles in the coating film are oriented in the longitudinal direction, the orientation direction can be modified to orient the magnetic powder particles isotropically in the horizontal direction within the coating surface, resulting in a decrease in viscosity. By using a highly magnetic paint, the magnetic powder particles, which were once oriented in the horizontal longitudinal direction within the coating surface, can be oriented isotropically in the horizontal direction within the coating surface, improving the surface smoothness of the magnetic layer. The present inventors have discovered that a magnetic disk can be obtained which can improve the output level and reduce fluctuations in the output level, has good short wavelength recording characteristics, and is highly reliable, leading to the present invention.

This invention will be explained below with reference to the drawings.

FIG. 1 shows an example of manufacturing a magnetic recording medium according to the present invention, in which a base film 2 fed out from a feed roll 1 is run at a constant speed along a guide roll 3 while a coater 4 coats a magnetic coating material 5. applied, and while the coating film 6 is in an undried state, the magnetic powder particles in the coating film 6 are guided between a pair of upper and lower orientation roll magnets 7 and 8 to make the magnetic powder particles in the coating film 6 non-oriented.
After that, it is introduced into a dryer 9 and completely dried, then wound onto a take-up roll 10, and then punched out into a circular shape to produce a magnetic disk.

Here, as shown in FIGS. 2 to 4, the orientation roll magnets 7 and 8 have different magnetic poles adjacent to each other and are vertically opposed to each other with the base film 2 in between. A large number of magnets 71 and 8 are magnetized by a partial magnetization method so that they are in a completely symmetrical positional relationship.
As shown in the expanded view of the magnetic force distribution in FIG. 4, each magnet 71 or 81 generates a magnetic field in the directions shown by the arrows in the front, rear, left and right directions. Furthermore, the magnets on each roll are arranged diagonally so that the rows of magnets are connected at the left and right ends of the roll. Further, each of the orienting roll magnets 7 and 8 is connected to arrows A and B as shown in FIG.
The magnets 71 and 81 are rotated at the same speed in the direction indicated by , and a large number of magnets 71 and 81 sandwich the base film 2 so that the same poles always face each other. However, due to the high speed rotation of the orientation roll magnets 7 and 8, a large number of opposing magnets 71, 81 pass through the coating film 6 on the base film 2 running between the orientation roll magnets 7 and 8. Therefore, a magnetic field parallel to the longitudinal direction (running direction) of the base film 2 and a magnetic field parallel to the width direction of the base film 2 are repeatedly applied to any position of the coating film 6 within the coating surface, and when applying the magnetic paint. The orientation direction of longitudinally oriented magnetic powder particles is modified. As a result, the magnetic powder particles in the coating film 6 become non-oriented, and the rectangular shapes in the longitudinal and width directions are almost equal. After drying, the magnetic disk produced by punching out a circular shape is used for recording and reproducing in the circumferential direction. A highly reliable magnetic disk with improved electromagnetic conversion characteristics without large fluctuations in output level can be obtained. In addition, since the orientation direction of the magnetic powder particles oriented in the longitudinal direction can be corrected when applying the magnetic paint, even if a highly viscous magnetic paint is used, the magnetic powder particles in the paint film 6 can be aligned within the surface of the paint film. By using a magnetic paint that can be made non-oriented, has a high viscosity, and has excellent dispersibility of magnetic powder, the surface smoothness of the magnetic layer can be sufficiently improved and short wavelength recording characteristics can be sufficiently improved. can do.

In this embodiment, a large number of magnets 71 and 81 are arranged on the circumferential surface of each of the orientation roll magnets 7 and 8 by a partial magnetization method. The present invention is not limited to the above-mentioned embodiments as long as the magnets are disposed in the magnets 71 and 81. For example, prefabricated magnets may be embedded in the positions of the magnets 71 and 81 on the circumferential surface of the orientation roll magnets 7 and 8. . In addition, instead of a roll-shaped orientation magnet, a large number of magnets are arranged by embedding them in a similar arrangement to the developed diagram of magnetic force distribution in Figure 4, or by magnetizing them using a partial magnetization method. Alternatively, it may be constructed in the form of a belt and rotated in the same manner as the roll-shaped orientation magnet. The large number of magnets arranged in such roll-shaped orienting magnets and belt-shaped orienting magnets may be arranged in a straight checkerboard pattern vertically and horizontally, but they may also be arranged in a slightly diagonal pattern as shown in Figure 4. By arranging them at an angle, the magnetic field strength applied to the coating film changes uniformly at all locations on the coating film, and the magnetic powder particles in the coating film are oriented more uniformly in the longitudinal and width directions. and becomes more completely unoriented.
It is preferable to tilt the magnets slightly diagonally so that each magnet generates a magnetic field in the front, rear, left and right directions.

A base film with an undried coating film between each of the opposing magnets, in which a large number of magnets with the same polarity face each other in the upper and lower directions sandwiching the base film, and are arranged so that magnetic fields are emitted from each opposing magnet in the front, back, left, and right directions. When the magnetic powder particles in the coating film are made non-oriented by introducing and extracting them, the magnetic field applied by each magnet varies depending on the viscosity of the magnetic paint, but the magnetic field is 20 to 20
It is preferable to give within the range of 00 oersted, and 2
A magnetic field of less than 0 oersted cannot sufficiently correct the orientation direction of the magnetic powder particles oriented in the longitudinal direction when applying magnetic paint, and a magnetic field greater than 2000 oersted will not make the magnetic field distribution uniform, resulting in partial may be oriented to some extent, causing fluctuations in the output level.

In addition, when using the orienting roll magnets of the above embodiments, the faster the rotation speed of each orienting roll magnet, the faster the magnetic field applied to the coating film can be switched, and the better the magnetic powder particles can be divided. Since it can be non-oriented, it is preferable that the running speed be at least faster than that of the base film.

Examples of the magnetic powder include acicular r-Fe203 powder, Fe3O4 powder, CO-containing 7-Fe2O3 powder, Co
Conventionally known magnetic powders such as Fe3O4 powder, CrO2 powder, Fe powder, CO powder, and Fe-Ni powder are widely used, and binder resins include vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, Conventional binder resins such as polyurethane resins, cellulose resins, and isocyanate compounds are widely used.

As the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethyl formamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described.

Example CO-containing r-Fe203 magnetic powder 270 parts by weight Powder VAGH (manufactured by U,C,C, USA, 80 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer) N1432J (manufactured by Nippon Zeon Co., Ltd. 15, acrylonitrile-butadiene) Copolymer) Coronate Nippon Boliure 1O〃Tan Kogyo Co., Ltd., trifunctional low molecular weight isocyanate compound) MS-500 (Asahi Carbon Co., Ltd. 34, carbon black) α Fe203 powder 11〃Methyl isobutyl ketone 200〃Toluene
200 This composition was mixed and dispersed in a ball mill for 48 hours to prepare a magnetic paint. The viscosity of magnetic paint is 80
The temperature was 35° C., the sliding speed was 102 sec'. This magnetic paint was coated to a thickness of 7 mm using the apparatus shown in Figure 1.
It was coated on both sides of a 5μ polyester film, subjected to a non-orientation treatment by applying a magnetic field of 500 degrees using orientation roll magnets 7 and 8, and dried to form a magnetic layer with a dry thickness of 3μ. Afterwards, it was punched out into a disk shape to create a magnetic disk.

Comparative Example 1 Example 1 except that the non-orientation treatment using the orientation roll magnet was omitted and the amounts of methyl isobutyl ketone and toluene used in the composition of the magnetic paint were changed from 200 parts by weight to 420 parts by weight, respectively. A magnetic disk was made in the same manner as in 1. The viscosity of magnetic paint is 10
．． 0 voice (temperature 35℃, sliding speed 102sec')
Met.

Comparative Example 2 In Example 1, instead of the device shown in FIG. 1, a device using a fixed magnet consisting of a pair of opposing magnets 11 and 12 instead of the orienting low-fire magnet was used as shown in FIG. A magnetic disk was produced in the same manner as in Example 1 except that the magnetic powder particles were oriented in the running direction (longitudinal direction) of the base film. The viscosity of the magnetic paint was 80 voids (temperature: 35° C., sliding speed: 102 sec').

Regarding the magnetic disks obtained in Examples and Comparative Examples, M n -Z at a recording wavelength of 1.0μ and a track width of 58μ.
When the reproduced output envelope was photographed and illustrated when the n-ferrite head was used, an envelope curve as shown in FIG. 6 was obtained. In FIG. 6, curve A shows the envelope curve of the magnetic disk obtained in Example 1, and curves A and B show the envelope curve of the magnetic disk obtained in Comparative Example 1. Further, curve C shows the letter envelope curve obtained in Comparative Example 2, and as is clear from these envelope curves, the one obtained in Example 1 is different from that obtained in Comparative Examples 1 and 2. The shape of the envelope curve is good and the output is high, which shows that the magnetic disk obtained by the present invention has extremely little variation in output level and can obtain high output.

In addition, the frequency characteristics of the magnetic disks obtained in Examples and Comparative Examples were investigated. FIG. 7 shows the results as a graph of the relationship between frequency and output. Graph A shows the relationship for the magnetic disk obtained in Example 1, and graph B shows the relationship for the magnetic disk obtained in Comparative Example 1. shows the relationship between As is clear from these graphs, the magnetic disk obtained in Example 1 (graph A) has a higher output than the magnetic disk obtained in Comparative Example 1 (graph B), and this shows that It can be seen that the recording characteristics have also been further improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an outline of an example of the method for manufacturing a magnetic recording medium of the present invention, FIG. 2 is an enlarged view of the same main part, and FIG.
An enlarged perspective view of the orientation roll magnet shown in FIGS.
Figure 4 is a developed diagram of the magnetic force distribution of the orientation roll magnet, Figure 5
FIG. 6 is an explanatory diagram showing an outline of a conventional method of manufacturing a magnetic recording medium, FIG. 6 is an envelope curve diagram of a magnetic disk obtained by this invention and a conventional magnetic disk, and FIG. 7 is an illustration of a magnetic disk obtained by this invention. FIG. 2 is a diagram showing the relationship between frequency and output of a disk and a conventional magnetic disk.

Claims (1)

[Claims] 1. Apply magnetic paint on the base film, and then arrange multiple magnets so that they are placed above and below the base film, and each magnet is independent, and adjacent magnets have different polarities. The magnetic field generating means is rotated or rotated on an endless orbit so that the magnets of the same polarity face each other in the vertical direction of the magnetic field generating means. A method for producing a magnetic recording medium, which comprises performing non-orientation treatment on powder particles and then drying them.