JPH0451887B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for manufacturing a high-density magnetic recording medium, and particularly to a method for manufacturing a recording medium that has good vertical alignment and uniformity and is suitable for high-density recording. Regarding manufacturing equipment. [Technical background of the invention and its problems] A magnetic recording medium consists of a support such as a polyester film and a magnetic layer provided thereon. In order to enhance the magnetic properties of the magnetic layer in a particular direction, it is common practice to apply a magnetic paint onto a support and then subject the magnetic particles to a magnetic field orientation treatment. In conventional magnetic recording media, a magnetic paint in which acicular magnetic particles are dispersed in a binder is applied onto a substrate, and then the paint film is undried and the magnetic particles are able to rotate in a specific direction within the surface of the paint film, e.g. Orientation processing has been performed in which a magnetic field is applied in the longitudinal direction of the tape. In this way, by orienting the magnetic particles, the squareness ratio of the magnetic recording medium has been increased and its sensitivity has been improved. However, as a result of progress in research into high-density recording in recent years, it has become possible to reduce residual magnetization in the longitudinal direction of the medium by using magnetic recording media in which the magnetic particles in the coating film are oriented in the plane of the film. There is a limit to the improvement of recording density in so-called longitudinal recording using
In order to achieve higher density, we use a recording medium in which the axis of easy magnetization of magnetic particles is oriented in a direction perpendicular to the medium surface, and record by residual magnetization in the direction perpendicular to the medium.
In other words, it has become clear that it is necessary to use perpendicular magnetization recording. A Co-Cr alloy film using vacuum technology is also known as a magnetic recording medium with perpendicular anisotropy used for such recording.
Research and development is progressing on a more practical type of perpendicular magnetic recording medium coated with magnetic particles. By the way, in order to apply a magnetic paint in which magnetic particles are dispersed in a binder onto a substrate and orient it vertically, it is necessary to apply a magnetic field perpendicular to the surface of the coating film while the coating film is wet and the magnetic particles can rotate. A method is used to orient the particles by giving At this time, if the viscosity of the paint film is low, the magnetic field is strong, or the applied time is long, the surface of the paint film may become rough or agglomeration may occur, and if the viscosity of the paint film is high or the magnetic field is low, If the magnetic field application time is extremely short, satisfactory vertical alignment cannot be obtained. In manufacturing a perpendicular magnetic recording medium coated with magnetic fine particles in this manner, it is difficult to select these conditions. [Object of the Invention] The present inventors have conducted various studies on methods to overcome these difficulties, and as a result, they have arrived at the present invention. It is an object of the present invention to provide a method and a manufacturing apparatus for manufacturing a magnetic recording medium with good reproducibility. [Summary of the Invention] That is, the present invention provides a coating material having perpendicular anisotropy, in which a paint containing fine magnetic particles is applied onto a substrate, and a magnetic field perpendicular to the coated surface is applied to orient the magnetic particles. In the manufacturing method and manufacturing equipment for high-density magnetic recording media, the degree of vertical orientation and surface roughness of the coating film after orientation treatment are detected, and the effectiveness of the orientation magnetic field strength and magnetic field orientation, which are the orientation treatment conditions, is immediately determined according to the results. A method and apparatus for manufacturing a high-density magnetic recording medium, characterized by adjusting and optimizing the time or coating viscosity during orientation. The above object is achieved by this manufacturing method and manufacturing apparatus. Next, the present invention will be explained in detail. When coating a paint containing magnetic particles on a substrate, applying a magnetic field perpendicular to the coating surface to orient it, and drying it to form a coating, if the orientation magnetic field is too weak, the magnetic field If the effective time for orientation is too short or the viscosity of the coating film is too high, satisfactory orientation may not be obtained; conversely, if the orientation magnetic field is too strong or the effective time for magnetic field orientation is too long, or If the viscosity of the coating film is too low, although a good degree of orientation can be obtained, the coating surface will become rough and the magnetic particles will agglomerate, making it unsuitable as a magnetic recording medium. Therefore, it is necessary to find appropriate values for these and perform orientation processing, but the appropriate values vary slightly from lot to lot of magnetic paint. Therefore, even when orientation processing is performed under predetermined setting conditions, there are many cases where appropriate conditions are not necessarily obtained. FIG. 1 is a block diagram of a method and apparatus for manufacturing a high-density magnetic recording medium according to the present invention. As shown in the figure, the surface roughness and degree of orientation of the coated and oriented film are detected during the process, and the data is transmitted to the calculation and control section. The arithmetic and control section processes the data, and based on this data, controls the coating process and orientation process to optimize the orientation magnetic field, the effective time of magnetic field orientation, or the viscosity of the coating film, as necessary. As the coating device used in the present invention, a gravure type, a reverse roll type, a doctor blade type, a dicoder type, and other types of devices can be used. Further, as the orientation device, either a permanent magnet method or an electromagnet method can be used. The drying device uses a drying method using warm air blown from a nozzle. As a device for detecting the surface roughness of a coating film, various detection means can be used, such as a method using light reflection, a method using a stylus, and a method using noise induced using a magnetic head. In addition, methods for detecting the degree of particle orientation in a coating film include a method based on changes in the intensity of X-ray diffraction lines of the coating film, a method based on the half-width of the rocking curve, a method based on the squareness ratio of the magnetization curve, a method used to determine the magnetic susceptibility, and a method based on the squareness ratio of the magnetization curve. A method of performing recording/reproduction using a recording waveform and evaluating it using a recording waveform, a method of calculating from a recording current-reproduction output curve, etc. can be used. Next, various types of analog manufacturing equipment can be used as calculation and manufacturing equipment, but it is also possible to use a method in which the output signal of the detection device is digitized and controlled using a microcomputer. Furthermore, methods for controlling the viscosity of the paint film include changing the ratio of the nonvolatile content of the magnetic paint to the solvent, evaporating part of the solvent in the paint film after application, and increasing the viscosity appropriately.
Various methods can be used, such as a method of changing the viscosity by changing the temperature of the coating film. In addition, as a method of controlling the orientation magnetic field, in the case of permanent magnets, there are methods such as changing the distance between the magnetic poles, providing a suitable magnetic path bypass and changing this, and in the case of electromagnets, changing the excitation current. Can be done. [Effects of the Invention] By using the method and apparatus of the present invention as described above, a high-density magnetic recording medium with a high degree of vertical alignment and good surface dispersion can be manufactured with good reproducibility. [Embodiments of the Invention] Next, embodiments of the manufacturing method and apparatus of the present invention will be shown. Example 1 Cobalt and titanium substituted fine particles of barium ferrite having a coercive force Hc800Oe and an average diameter of about 0.09μm and exhibiting uniaxial magnetic anisotropy are mixed and dispersed well together with a dispersant, a binder, a lubricant, and an organic solvent. This is made into a magnetic paint, a hardening agent is added to this, and the thickness is 15μ.
The film was coated on a polyethylene terephthalate support of 500 mL to a dry thickness of about 4 μm. After generating a vertical magnetic field using an electromagnet and applying it to this undried coating film to orient the particles, the solvent in the coating film is evaporated.
The orientation state was fixed by increasing the viscosity of the coating film. The surface roughness of the coating film was calculated from the light reflectance (gloss). Furthermore, the particle orientation rate of the coating film was calculated from the measurement of the magnetic susceptibility of the coating film. Note that these calculations use data obtained by previously measuring the relationship between surface roughness and glossiness, and between orientation rate and magnetic susceptibility. When the surface roughness is S and the orientation rate is R, F= as an index.
Using R/S, coating and orientation drying was carried out while keeping the orientation magnetic field and other conditions constant and controlling the solvent content in the supplied paint by feedback so that the bottom was the maximum. The solvent content was controlled by preparing a magnetic paint with a solvent content of 60% by weight and a paint with a solvent content of 70% and changing the mixing ratio of the two. The thus prepared coating film was supercalendered and cured, and then cut into 1/2 inch width pieces to obtain magnetic tape 1. Table 1 shows various properties of the tape. Example 2 In Example 1 above, instead of controlling the solvent content of the supplied paint, the solvent content of the supplied paint was kept constant at 70% by weight, and a dryer zone was provided between the coating process and the orientation process so that the lower value was the maximum. The dryer temperature was feedback-controlled at 30 to 60°C so that the orientation treatment was performed at an optimized coating viscosity. Table 1 shows the properties of tape 2 obtained by supercalendering, curing and cutting this coating film. Example 3 Using the same magnetic paint as in the above example, the solvent content was reduced.
Apply a constant amount of 65% by weight, and apply it so that the lower value is maximized under the effective magnetic field orientation time of about 0.5 seconds.
The orientation magnetic field was feedback controlled between 0 and 10 KOe. Table 1 also shows the properties of tape 3 obtained by supercalendering, curing, and cutting the thus obtained coating film. Example 4 Instead of controlling the orientation magnetic field in Example 3, it was kept constant at 4KOe, and the effective time of magnetic field orientation was approximately 0.2
Feedback control was performed so that the lower value reached its maximum within ~1.5 seconds. Tape 4 obtained by subjecting the thus obtained coating film to supercalender treatment, curing, and cutting.
The characteristics are shown in Table 1. Example 5 Furthermore, the effective time of magnetic field orientation was set constant at about 0.5 seconds,
The solvent content of the paint and the orientation time were successively controlled in feedback so that the lower value was the maximum. Table 1 also shows the properties of tape 5 obtained by supercalendering, curing, and cutting the thus obtained coating film. Comparative Example: Supplying 65% of paint solvent content without performing feedback control of orientation conditions as described in the present invention.
A tape was prepared by performing orientation treatment with an orientation magnetic field of 6 KOe and a constant effective time of magnetic field orientation of 0.5 seconds, followed by supercalendering, curing and cutting. The tape properties are shown in Table 1-6. By comparing the Examples described above with the results of Comparative Examples, it was found that by using the manufacturing method and apparatus of the present invention, coated magnetic recording media with good vertical alignment, surface properties, and dispersibility can be produced with good reproducibility. It turns out that it can be manufactured. 【table】

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the present invention.

Claims (1)

[Claims] 1. Highly perpendicular anisotropy, in which a paint containing fine magnetic particles is applied onto a substrate, and a magnetic field perpendicular to the coating surface is applied to orient the magnetic particles. A method for manufacturing a high-density magnetic recording medium, which is characterized by detecting the degree of vertical orientation and surface roughness of a coating film after orientation treatment, and immediately adjusting and optimizing the orientation treatment conditions according to the results. A method for manufacturing a recording medium. 2. A method for manufacturing a high-density magnetic recording medium as set forth in claim 1, characterized in that the orientation treatment conditions include adjusting and optimizing the orientation magnetic field strength. 3. A method for manufacturing a high-density magnetic recording medium as set forth in claim 1, characterized in that the effective time of magnetic field orientation is adjusted and optimized as the orientation treatment condition. 4. A method for manufacturing a high-density magnetic recording medium as set forth in claim 1, characterized in that the orientation treatment conditions include adjusting and optimizing the viscosity of the coating film during orientation. 5. In an apparatus for manufacturing a high-density magnetic recording medium having perpendicular anisotropy by applying a paint containing fine magnetic particles onto a substrate and applying a magnetic field perpendicular to the coated surface to orient the magnetic particles. , has a detector for the degree of vertical orientation of the coating film after orientation treatment and a detector for the surface roughness of the coating film, and depending on the output signals of these detectors, the orientation magnetic field strength, the effective time of magnetic field orientation, or the coating film at the time of orientation are detected. A high-density magnetic recording medium manufacturing apparatus characterized by having an operation mechanism for controlling viscosity.