JPS59203243A - Production for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with a good electromagnetic conversion characteristic and high reliability by bringing a magnetic film attached on the base film by painting into and out between magnets facing each other in the state where a magnetic film is being undried, and orientating magnetic powder particles in a prescribed direction to dry the magnetic applied film. CONSTITUTION:Magnets 1 and 2 having yokes 11 and 21 formed with plate bodies consisting of triangular permeable materials are arranged to face each other, and a base film 4 having an undried magnetic applied film 3 is run between yokes 11 and 21. A magnetic field indicated by dotted lines acts upon the base film 4 to orientate magnetic powder particles in the applied film 3 so that their angular shapes in the breadthwise direction and the lengthwise direction are equalized approximately. When the base film is punched into a round after the film 3 is dried, a large output difference is not generated at a recording/ reproducing time in the circumferential direction of an obtained magnetic disc, and the electromagnetic conversion characteristic is improved, and thus magnetic disc with high-reliability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a highly reliable magnetic disk in which magnetic powder particles in a magnetic layer have no directionality, have good electromagnetic characteristics, and are highly reliable. The present invention relates to a method of manufacturing magnetic recording media such as.

Among magnetic recording media, those in which magnetic recording is performed in the longitudinal direction, such as magnetic tape, have improved electromagnetic conversion characteristics by orienting acicular magnetic powder in the magnetic layer in the longitudinal direction.

In general, a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components is applied onto a substrate such as a polyester film, dried to form a magnetic layer, and then punched out in a circular shape. Since magnetic recording is performed in the circumferential direction of magnetic disks manufactured by the magnetic disks, good electromagnetic conversion characteristics cannot be obtained if the acicular magnetic powder is oriented in the longitudinal direction of the substrate, as is the case with magnetic tapes.

For this reason, in conventional magnetic disks, after applying the magnetic paint onto the base film, it is dried without any magnetic field orientation, and the acicular magnetic powder contained in the magnetic layer is made unoriented. Recording and reproduction in the circumferential direction is performed satisfactorily.

However, when drying without any magnetic field orientation,
Although it is possible to make the acicular magnetic powder almost non-oriented, when applying the magnetic paint onto the base film, the magnetic powder particles in the magnetic layer are slightly oriented in the longitudinal direction of the base film due to the shearing force applied to the paint. However, as a result, when recording and reproducing in the circumferential direction, there are drawbacks such as a large output difference.Therefore, magnetic disks with sufficiently good electromagnetic conversion characteristics and high reliability are still available. has not been obtained.

As a result of intensive studies to overcome this problem, the inventors applied magnetic paint to the base film, and then, while it was still undried, applied different polarities on at least both sides of the base film in the width direction. When the magnetic powder particles are introduced between the opposed magnets arranged in this way, the magnetic powder particles slightly oriented in the longitudinal direction in the coating film are caused by the magnetic field applied by the opposed magnets on both sides of the base film arranged in this way. The orientation direction is corrected in the width direction of the base film or in a direction tilted perpendicularly from the width direction, and furthermore, from these opposing magnets toward the center in the width direction of the base film, the area near the center of the base film is separated from the coating film and the edges are separated from the coating film. When each magnetic field generating means is extended so that it approaches the coating film as it goes towards the end,
The magnetic field applied by each of these magnetic field generation means is applied to further improve the orientation direction of the magnetic powder particles in the coating film, and as a result, the directionality of the magnetic powder particles is eliminated, and the width direction of the resulting magnetic layer The rectangular shapes in the long plane direction are almost equal,
It was discovered that a magnetic disk with good electromagnetic conversion characteristics and high reliability can be obtained without causing a large difference in the direction of output during recording and reproduction in the circumferential direction, and this invention has been completed.

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

FIG. 1 and FIG. 2 show an example of a magnetic field orientation device according to the present invention. In the figure, 1 and 2 are N-3 facing magnets arranged with different poles facing each other in positions close to both sides in the width direction of the base film 4 having an undried coating film 3, and 11 is integrally connected from the facing magnet 1. A yoke 21 made of an extended magnetically permeable material is a yoke made of a magnetically permeable material extended integrally with the facing magnet 2, and the base film 4 having the undried magnetic coating film 3 is formed by such facing magnet work. .

2, runs between t and yoke 11.21. York 11
and 21 are each composed of a triangular plate made of a magnetically permeable material. At the bottom of the base film 4, near the center of the base film 4, the coating film 3 separates from the coating film 3, and as it approaches both ends, it approaches the coating film 4. The inclined surfaces of the triangular plates extend from the opposing magnets 1 and 2 so as to descend toward the center of the base film 4. However, a magnetic field as shown by the dotted line acts on the Heath film 4 having the undried coating film 3 running between the N-3 opposing magnets 1 and 2 with the yokes 11 and 21 extending therefrom. The magnetic powder particles in the coating film 3, which are slightly oriented in the longitudinal direction of the base film 4 due to the shearing force applied during application of the magnetic paint, are oriented in the width direction at the center of the coating film 3 and from the vertical direction to the width direction at both ends. The orientation direction is corrected in the direction of inclination. As a result, the magnetic powder particles in the coating film 3 become unoriented, and the rectangular shapes in the width direction and longitudinal direction are almost equal. The electromagnetic conversion characteristics are improved without causing a large output difference, and a magnetic disk with low reliability can be obtained. Here, each opposing magnet 1
The same effect can be obtained by correcting the orientation direction of the magnetic powder particles by simply arranging the opposing magnets 1 and 2 without extending the yokes 11 and 21 from the base film center. There is a tendency for the magnetic field to become weaker as the yokes 11 and 21 extend toward the base film 4. If the yokes 11 and 21 are extended, this tendency can be suppressed and a good magnetic field can be applied to the entire coating 3 on the base film 4. A more preferable result can be obtained by extending 21 and 21.

FIG. 3 shows another example of the magnetic field orientation device according to the present invention, in which the yoke 22 from the opposing magnet 2 of the device in the above example is connected to the base film 4 having the undried coating film 3. The base film 4 runs between the opposing magnets 1.2 and the yoke 11.22. In this case, since the yokes 11 and 22 extending from the opposing magnets 1 and 2 face each other with the base film 4 having the undried coating film 3 in between, the coating film 3 is When a magnetic field as shown is applied, the orientation of the magnetic powder particles in the coating film 3 is modified from the perpendicular direction to a direction inclined in the width direction, and as a result, as in the case of the previous example, the magnetic powder particles in the coating film 3 are The magnetic powder particles are non-oriented and have approximately the same square shape in the width and length directions. After drying, the magnetic disks produced by punching out circular shapes have improved electromagnetic characteristics.
Reliability is also improved.

In each of the magnetic field orientation devices described above, the shape of the yoke is not limited to a triangular plate shape, but as long as it is separated from the coating film near the center of the base film and approaches the coating film toward both ends, The inclined surface of the yoke having a predetermined angle may be a curved surface of various shapes, for example, a curved surface as shown in FIG. 4. In addition, as shown in Figures 5 and 6, a long plate-shaped or rod-shaped yoke is attached to each opposing magnet so that it is spaced apart from the coating film near the center of the base film and asymptotically approaches the coating film toward both ends. It may also be extended and inclined from the top. Further, the magnetic field generating means extending from each opposing magnet is not limited to the yoke made of a magnetically permeable material as described above, as long as it can generate a magnetic field. It may be extended. Furthermore, in each of the magnetic field orientation devices described above, a large number of yokes extending from each opposing magnet may be provided as shown in FIG.
If a large number of yokes are installed in an extended manner, the magnetic field applied to the coating film can be easily adjusted, and exactly the same effect as described above can be obtained.

Using the magnetic field orientation device as described above, the base film 4
When making the magnetic powder particles in the above undried coating film 3 non-oriented, the ratio of the square shapes in the width direction and the long direction, that is, the orientation ratio (square shape in the longitudinal direction / square shape in the width direction) is 0. It is preferable that the orientation ratio be approximately equal within the range of .95 to 1.05. If the orientation ratio is outside this range, the output difference that occurs during recording and reproduction in the circumferential direction will be large (and will not be good). In order to make the square shapes in the width direction and length direction almost equal, it is necessary to apply a magnetic field of 20 to 150 oersteds in width, depending on the viscosity of the magnetic paint. A magnetic field of less than 20 oersted cannot sufficiently correct the orientation direction of the magnetic powder particles oriented in the longitudinal direction when applying the magnetic paint, and a magnetic field greater than 150 oersted will cause the magnetic powder to be applied in the width direction. If it is too oriented in the circumferential direction, the difference in output that occurs during recording and reproduction in the circumferential direction becomes large, making it impossible to obtain good electromagnetic conversion characteristics.

Figure 8 is a graph showing the relationship between the magnetic field strength in the width direction and the orientation ratio. Graph A shows a magnetic paint with a viscosity of 6.0 poise (temperature 35°C, sliding speed 105 sec'). After coating with a reverse roll coater, changes in the orientation ratio were measured while varying the strength of the magnetic field in the width direction using the magnetic field orientation device shown in FIG. 1, and the results are shown in a graph. In addition, graph B has a viscosity of 2.5 poise (temperature 3
The graph shows the relationship between the strength of the magnetic field in the width direction and the orientation ratio in the same way as graph A, except that a magnetic paint with a sliding speed of 105 seconds (5°C and 105 seconds) was used, and graph C shows the relationship between the magnetic field strength in the width direction and the orientation ratio. The relationship between the strength of the magnetic field in the width direction and the orientation ratio was determined in the same manner as in graph A, except that a magnetic paint with a temperature of 35 °C and a sliding speed of 1055 ec-' was applied using a gravure roll coater. It is expressed as a graph.As is clear from these graphs, there are differences depending on the viscosity of the magnetic paint, but it is
When a magnetic field of 0 oersted is applied, the orientation ratio is 0.95~
It can be seen that the orientation ratio is within the range of 1.05, and the orientation ratio is sufficiently improved.

In this way, the correction of the orientation direction of magnetic powder particles due to the shearing force when applying magnetic paint using a magnetic field orientation device differs depending on the viscosity of the magnetic paint. Favorable results are obtained when the viscosity is between 0.8 and 6.0 voids at a temperature of 35" C1 and a shear rate of 105 sec', and the square shape of the magnetic powder particles in the width and length directions of the coating film is are almost equal, and a magnetic disk with excellent electromagnetic conversion characteristics and good reliability can be obtained.

Further, as the magnetic powder, acicular magnetic powder with an axial ratio (major axis/minor axis) of 3 or more is preferably used, such as acicular T Fe2O3 powder, Fe3O4 powder, C, o-containing r Fe2O3 powder, Co-containing Fe3O4 powder, Cr
Conventionally known magnetic powders such as O2 powder, Fe powder, CO powder, and Fe-Ni powder are widely used.

Furthermore, as binder resins, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, polyurethane resins, cellulose resins, and isocyanate compounds are widely used. are methyl isobutyl ketone, methyl ethyl ketone,
Cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethylformamide, 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 I Co-containing 'r Fe203w1 powder 270 parts by weight (particle size (long axis) 0.4μ, axial ratio (long axis/short axis) 10) VAGH (manufactured by U, C, C, USA, 80% chloride) (Vinyl-vinyl acetate-vinyl alcohol copolymer) N1432J (manufactured by Nippon Zeon Co., Ltd. 15, acrylonitrile-butadiene copolymer) Coronate Nippon Polyurethane 10 (manufactured by Tan Kogyo Co., Ltd., trifunctional low molecular weight isocyanate compound) H3- 500 (manufactured by Asahi Carbon Co., Ltd. 34, carbon blank) ct-Fe203 powder 11〃Methyl isobutyl ketone 420〃Toluene
420 This composition was mixed and dispersed in a ball mill for 48 hours to prepare a magnetic paint. The viscosity of magnetic paint is 0
．． The temperature was 8 poise (temperature: 35° C., rubbing speed: 105 sec'). This magnetic paint was applied to both sides of a polyester film with a thickness of 75 μm, and a magnetic field orientation device shown in FIG.
A magnetic field of 0 oersted was applied for non-orientation treatment, and the material was dried to form a magnetic layer with a dry thickness of 3 μm. After that, a disk-shaped piece was punched out to make a magnetic disk.

Comparative Example 1 A magnetic disk was produced in the same manner as in Example 1, except that the non-orientation treatment using the magnetic field orientation apparatus shown in FIG. 1 was omitted. The viscosity of magnetic paint is 0.8 poise (
The temperature was 35° C. and the shear rate was 105 sec'. Regarding the magnetic disks obtained in the examples and comparative examples,
The orientation ratio (square in the longitudinal direction/square in the width direction) and the output difference over one revolution of the magnetic disk were measured.

The table below shows the results.

As is clear from the table above, the magnetic disk obtained in Example 1 has an orientation ratio of approximately 1 compared to that obtained in Comparative Example 1.
It is found that the magnetic disk obtained by the manufacturing method of the present invention has good electromagnetic conversion characteristics and improved reliability.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of the magnetic field orientation device used in the manufacturing method of the present invention, FIG. 2 is a plan view of the same, and FIGS. 3 to 6 are front views showing other examples of the same magnetic field orientation device. , FIG. 7 is a plan view showing another example of the same magnetic field orientation device, and FIG. 8 shows the strength of the magnetic field in the width direction and the magnetic powder particles in the coating film when manufacturing a magnetic recording medium by the manufacturing method of the present invention. FIG. 1.2... Opposing magnet, 11, 21. 22... Yoke (magnetic field generating means), 3... Coating film, 4... Heath Film Patent Applicant Hitachi Maxell Ltd. Figure 7 Figure 8 Figure Magnetic field strength Oe)

Claims (1)

[Scope of Claims] 1. Magnetic paint is applied onto a base film, and then, while the paint is not dried, opposing magnets are arranged at least on both sides of the running base film in the width direction, with different poles facing each other. A method for manufacturing a magnetic recording medium 2, characterized in that the magnetic powder particles in the coating film are oriented so that the square shapes in the width direction and the longitudinal direction are approximately equal, and then dried. A magnetic field generating means of a length that does not reach the center of the base film is applied from each opposing magnet toward the center in the width direction of the base film, and a coating film is applied near the center of the base film corresponding to the top or bottom surface of the base film. A base film with an undried coating film is introduced between these magnetic field generating means and opposing magnets on both sides, and the magnetic field in the coating film is removed. A method for manufacturing a magnetic recording medium according to claim 1, in which powder particles are oriented so that the square shapes in the width direction and the longitudinal direction are approximately equal, each magnetic field generating means extending from each opposing magnet on both sides. However, it forms a left and right pair corresponding to one side of the base film, and for either side of the base film, it is separated from the paint film near the center of the base film, and asymptotically approaches the paint film as it goes to both ends. A method 4 for producing a magnetic recording medium according to claim 2, in which the magnetic recording medium is produced by the opposed magnets on both sides and the magnetic field generating means extended from these opposed magnets. The magnetic field applied to the coating film is from 20 to 150 oersteds, the method 5 for producing a magnetic recording medium according to claims 1 to 3, each magnetic field generating means extending from each opposing magnet on both sides. is a yoke made of a magnetically permeable material, a method 6 for producing a magnetic recording medium according to claims 2 to 4, wherein the viscosity of the magnetic paint applied on the base film is 35° C. and a sliding speed of 105° C. 0.8 to 6.0 in sec'
A method 7 for manufacturing a magnetic recording medium according to claims 1 to 5, which is a BOYS, and claims 1 to 6, wherein the magnetic powder in the magnetic paint is an acicular magnetic powder. Method for manufacturing a magnetic recording medium