JPH0444326B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium, and particularly to a method of manufacturing a type of magnetic recording medium used for angle or rotational control.

Prior Art Conventionally, magnetic recording media used for angle or rotation control include those with a magnetic coating formed on the outer periphery or flat surface of a circular metal base, circular plastic magnets, or sintered rings. Some have magnets attached. This type of magnetic recording medium has its magnetic part magnetized with equally spaced magnetization patterns, is attached to a rotating system, and the magnetization pattern is detected by a magnetic head or magnetoresistive element to indicate the rotation speed and rotation angle. It is used for

However, conventional magnetic recording media on which magnetic coatings are formed have disadvantages of poor productivity and high cost because they require grinding. This is because spraying is generally used as the coating method, but to obtain the required film thickness of 30 to 100 μm, multiple coatings must be applied, and each coating must be dried.
Productivity is poor. In addition, the surface of the paint film becomes rough,
Coating film grinding is required to reduce noise, resulting in high costs.

Further, in the case of a conventional magnetic recording medium of the type in which a circular plastic magnet is bonded, it is difficult to obtain high dimensional accuracy, so there is a drawback that highly accurate characteristics cannot be obtained. In other words, the dimensional accuracy of the plastic magnet itself can be improved, but when it is bonded to a metal base, misalignment and deformation occur, and the roundness and center runout cannot be kept within 100μ. Difficult to suppress.
By grinding the surface of the magnet after adhering it, it is possible to improve roundness and improve accuracy, but this increases the cost.

Furthermore, in the case of a conventional magnetic recording medium with a ring magnet bonded to it, a sintered molded magnet is used, but it has the drawback of requiring grinding after molding, which complicates the process and increases costs. In addition, it is difficult to align and keep the runout within 100μ when installing it on a rotating system.
This is the same drawback as with the plastic magnets mentioned above.

In recent years, as this type of magnetic recording medium, a kneaded type magnetic recording medium has been developed, which is made of a material such as nylon resin kneaded with a magnetic material such as barium ferrite, and is formed entirely including the base by injection molding. ing. However, since these kneaded type magnetic recording media have a uniform composition as a whole, it has been difficult to satisfy the conflicting properties of mechanical strength and magnetic properties. This is because, in terms of magnetic properties, the higher the content of the magnetic material, the better, but if this is done, the material becomes brittle and easily chipped, resulting in a decrease in mechanical strength. Therefore, in such cases, it has been necessary to compromise on a composition that provides both magnetic properties and mechanical strength to a certain degree.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the conventional problems as described above, and to provide an inexpensive magnetic recording medium with high precision and excellent mass productivity, and a method for manufacturing the same.

Structure of the Invention In the method for manufacturing a magnetic recording medium according to the present invention, a substrate to which a magnetic layer is to be applied is placed in a mold in advance, and a magnetic material and a thermosetting resin are placed in the gap between the surface of the substrate and the mold. A magnetic layer is integrally formed on the surface of the substrate by filling the resin with a kneaded material and then curing and molding the resin by applying pressure and heating.

Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying drawings.

FIG. 1 is a perspective view showing an embodiment of a magnetic recording medium according to the present invention. The magnetic recording medium of this embodiment includes a circular base 1 and a magnetic layer 2 formed by integrally molding a material obtained by kneading a magnetic material and a resin onto the outer peripheral surface of the circular base 1.

FIG. 2 is a perspective view showing another embodiment of the magnetic recording medium according to the present invention. The magnetic recording medium of this embodiment includes a disc-shaped substrate 3 and a magnetic layer 4 formed by integrally molding a material obtained by kneading a magnetic material and a resin onto the upper surface of the disc-shaped substrate 3. It's summery.

In the embodiments shown in FIGS. 1 and 2, the magnetic layer is provided on the outer peripheral surface of the circular base or the upper surface of the disc-shaped base, but in the case of a cylindrical base, etc., the magnetic layer is provided on the inner peripheral surface of the cylinder. It is also possible to form the magnetic layer integrally with the magnetic layer, and the present invention also includes such a case.

Next, an embodiment of the method for manufacturing a magnetic recording medium according to the present invention will be described with reference to FIG.

As shown in a schematic cross-sectional view in FIG. 3, a base body 6 having a desired shape is placed in advance in the lower mold 5 of the mold. The material for forming the base body 6 is preferably one that is less deformable and light, such as plastic, fiber-reinforced plastic, inorganic material-added reinforced plastic, metal, etc., such as polyphenylene sulfide, nylon, etc.
Polycarbonate, iron, aluminum, copper, steel, etc. may be used. Next, the gap between the inner circumferential surface of the lower mold 5 and the outer circumferential surface of the base body 6 is filled with a material 7 obtained by kneading a magnetic material and a resin. In this case, a mold release material 9 such as silicone for preventing adhesion is provided on the inner peripheral surface of the lower mold 5.
It is a good idea to apply it. Further, the magnetic material is not particularly limited, but preferably has a small particle size, such as r-Fe ₂ O ₃ , Fe ₃ O ₄ , Co
−rFe ₂ O ₃ , Co−Fe ₃ O ₄ , CrO ₂ , Ba ferrite,
Sr ferrite, rare earth magnet material (SmCo ₅ ,
Sm ₂ Co ₁₇ etc.) are used. The resin to be kneaded is preferably a thermosetting resin that is initially in a liquid state and solidified by pressure heat treatment due to the manufacturing method, such as unsaturated polyester, acrylic resin, epoxy resin, urethane resin, etc. . Further, the magnetic material and the resin may be kneaded by, for example, a conventional mixing device such as a kneader or a three-roll mill for an appropriate time. After that, the upper mold 8 is placed over the lower mold 5, and these are inserted between the flat pressure heat presses 11A and 11B that have a built-in heater 10, and the resin is hardened and molded by applying pressure and heating. good. It is preferable to form a recess 8A on the lower surface of the upper die 8 at a position corresponding to the vicinity of the outer periphery of the base body 6 for escape of the kneaded material 7.

A magnetic recording medium formed in this manner is shown in a plan view and a front view, respectively, in FIGS. 4A and 4B.

According to such a pressure and heat molding method, the magnetic layer can be made homogeneous, and since the stress applied to the substrate during molding is low, distortion such as deformation of the substrate can be prevented. Instead of such a pressure and heat molding method, it is possible to use an injection molding method, but this method involves injecting a material made by kneading molten resin and magnetic material into the gap between the mold and the base, and then cooling and hardening. Since the magnetic material is molded in a single layer, the flow state differs near the gate where it is injected, so it is difficult to avoid uneven distribution and orientation of the magnetic material, resulting in areas with non-uniform magnetic properties.
Furthermore, since the injection pressure is high, strong stress is applied to the substrate, making it easily deformed, which is undesirable.

A magnetic recording medium having a shape specifically shown in FIG. 4 was fabricated using the manufacturing method described with reference to FIG. 3 and the following specifications.

Magnetic layer forming material Magnetic material: rFe ₂ O ₃ (MRM400 Toda Kogyo Co., Ltd.) 60 parts Resin: Unsaturated polyester 40 parts Base material: Polyphenylene sulfide (PPS) resin (Shin-Etsu Chemical) Dimensions: Outer diameter φ22 .5mm Thickness 5mm Magnetic layer thickness 1.5mm Molding compression molding pressure: 100Kg/cm ² Molding temperature: 160℃ Molding time: 2 minutes The magnetic recording medium prototyped with the above specifications has the following good characteristics. I was able to do that.

Magnetic properties Coercive force: 400Oe Residual magnetic flux density: 900G Electromagnetic conversion characteristics As shown by the solid curve A in Figure 5, a uniform and sufficient output was obtained.

Dimensional accuracy Roundness: 1μ or less Runout (runout on the outer periphery based on the center hole):
±10μ or less The dotted line curve B in FIG. 5 shows the output waveform of a magnetic recording medium similar to the above-mentioned magnetic recording medium prototyped according to the present invention and formed by the above-mentioned injection molding method. There is. This dotted curve B
As shown in B', in injection molded magnetic recording media, large output fluctuations occur at the weld portion of the magnetic layer caused by injection molding. By comparing these curves A and B in FIG. 5, it can be seen that the reproduced output waveform of the magnetic recording medium according to the present invention has much less fluctuation, and the magnetic recording medium according to the present invention has better and more uniform magnetic properties. It can be seen that the dimensional accuracy is excellent.

By polishing the magnetic layer of the medium manufactured as described above, it is possible to obtain a highly accurate medium with even less center runout.

Effects of the Invention According to the method of manufacturing a magnetic recording medium according to the present invention, the injection molding method produces a weld part in the magnetic layer and causes a large output fluctuation when magnetized, whereas the method produces uneven distribution of the magnetic material. First, magnetic layers having uniform magnetic properties can be mass-produced, and shapes, dimensions, etc. can be selected from a wide range. Further, there is an advantage that a recording medium with excellent mass productivity and low cost can be supplied without causing deformation or the like to the base.

Furthermore, compared to conventional kneaded type magnetic recording media, the magnetic recording medium produced by the manufacturing method of the present invention has a two-layer structure consisting of a base and a magnetic layer, so the magnetic properties are determined only by the magnetic layer. Since the mechanical properties can be assigned only to the substrate, there is flexibility in that materials satisfying both properties can be selected as the magnetic layer material and the substrate material, respectively, independently of each other. Also, regarding the overall weight,
The specific gravity of conventional mixed-type magnetic recording media, in which a magnetic material (for example, ferrite with a specific gravity of about 5) is kneaded throughout, is 3 to 4, whereas In magnetic recording media, the heavy magnetic material is contained only in the surface magnetic layer, so the overall weight can be reduced, and its specific gravity is 1.5 to 1.5.
2, it can be made about 1/2 the weight of the conventional kneading mold.

Furthermore, the magnetic recording medium manufactured by the manufacturing method of the present invention has an advantage over conventional coating-type magnetic recording media in that the thickness of the magnetic layer can be arbitrarily selected. That is, the magnetic layer thickness is an important factor for magnetic recording, and there is an optimum thickness depending on the conditions. If it is thin, the playback output will be small,
If it is too thick, there are problems such as a peak shift (distortion of the reproduced waveform) and a decrease in the reproduction output due to film thickness loss. From this point of view as well, the present invention is advantageous in that it is possible to select the magnetic layer thickness within a wide range, so that in many cases a magnetic layer with an optimum thickness can be formed.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a magnetic recording medium according to an embodiment of the present invention, FIG. 2 is a perspective view showing another embodiment of a magnetic recording medium according to another embodiment of the present invention, and FIG. 3 is a perspective view showing a magnetic recording medium according to another embodiment of the present invention. 4A and 4B are a plan view and a front view of a magnetic recording medium formed by the manufacturing method explained in connection with FIG. 3; , FIG. 5 is a diagram showing an example of a reproduced output waveform from the magnetic recording medium of FIG. 4. 1, 3, 6...Substrate, 2, 4, 7...Magnetic layer, 5...
Lower mold, 8... Upper mold, 11A, 11B... Flat pressure heat press.

Claims (1)

[Claims] 1. A substrate to which a magnetic layer is to be applied is placed in a mold in advance, and the gap between the surface of the substrate and the mold is filled with a material obtained by kneading a magnetic material and a thermosetting resin.
A magnetic recording medium characterized in that a magnetic layer is integrally formed on the surface of the substrate by hardening and molding the resin by applying pressure and heating. Production method.