JPS63148417A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To ensure the stable production of a magnetic recording medium of high quality by setting a range of magnetic field intensity and at the same time setting variably the relationship between the frequency (Hz) and the applying speed within a specific range to easily set a satisfactory random orientation treatment. CONSTITUTION:The magnetic grains are orientated at random in their undried states by a frequency variable AC magnetic field generating device 4 for a magnetic liquid applied on a nonmagnetic supporter 2. In this case, the frequency (Hz) produced by the device 4 is set so that the absolute numeric value is variable within a 0.1-1 range against the traveling speed, i.e., the passing speed (m/min) in the device of the supporter 2. At the same time, the intensity of an AC magnetic field to be applied is set within a 0.1-1 range of the reluctance force of a magnetic material. Under such conditions, an orientation process is carried out. Then, an undried magnetic application layer is dried and hardened through a drying device 5. Thus, a sheet type magnetic recording medium is obtained. In such a way, the random orientation process is easily set even in a production mode of various magnetic recording media. Then, it is possible to obtain a magnetic recording medium of the stable quality.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a magnetic recording medium, and in particular to a method for manufacturing a magnetic recording medium suitable for manufacturing a coated disk medium such as a floppy disk. This relates to a manufacturing method.

(Prior Art) Magnetic recording media such as magnetic disks and magnetic tapes generally have a strip-shaped non-magnetic support that is continuously transported in the longitudinal direction of the support while being strongly immersed in a binder dissolved in a solvent. It is manufactured by applying a magnetic liquid containing magnetic fine particles dispersed therein, then drying and solidifying the magnetic liquid, and then punching or cutting the support.

However, in the manufacture of magnetic disks, if ferromagnetic particles are arranged in a particular direction during manufacture and anisotropy occurs in the magnetic recording medium, anisotropy also occurs in the magnetic and electrical properties in various directions. For example, if the magnetic particles are arranged along the direction K of applying the magnetic liquid (i.e. the direction of transport of the non-magnetic support), the magnetic head 9 does not scan linearly as in the case of a magnetic disk, but in a circular direction. When scanning concentrically in the circumferential direction, the reproduction output signal level in this coating direction is higher than that in the other direction, and as a result, the reproduction output signal level read from the magnetic disk changes as the disk rotates. (This phenomenon is generally called modulation.) In particular, when the coating thickness of the magnetic layer is reduced or the coating speed is increased, the magnetic particles are susceptible to mechanical effects, and a state in which they appear to be oriented in a specific direction occurs at a high rate. Therefore, in the conventional manufacturing of magnetic disks, etc., in order to solve the above-mentioned problem of linear orientation of magnetic particles caused by the flow orientation during magnetic liquid application, a magnetic field is applied while the magnetic liquid is not dry. As mentioned above, a method of applying a magnetic field to a magnetic liquid while it is not dry is disclosed in Japanese Patent Application Laid-open No. 198545/1983. A method of applying an alternating magnetic field as disclosed in the publication is known.

(Problem to be Solved by the Invention) However, when the above-mentioned random orientation treatment using an alternating magnetic field is applied to a method for manufacturing a magnetic recording medium, it is affected by the liquid composition and coating speed, and if these changes, the random orientation treatment may not work properly. It turned out that I wasn't going. Also, even if the liquid has the same composition, it may be completely different due to subtle changes in the dispersion state or magnetic properties of the magnetic powder. It was found that the magnetic field conditions for randomization changed, making stable random orientation processing impossible.

When these causes were ascertained, it was found that for the first problem, there is an optimum frequency for the liquid composition and coating speed, y<support running speed.

In other words, if one frequency is too high, the movement of the magnetic body will not be able to follow changes in the magnetic field, and the magnetic body will align in a direction perpendicular to the direction of the applied magnetic field (in the lateral direction relative to the longitudinal direction of the magnetic field applied). It turned out that this is because, conversely, if the frequency is too low, the magnetic material aligns in the direction of the magnetic field application.

In addition, regarding the second problem, because it is randomized based on the balance between liquid composition and magnetic field strength, it is likely to be affected by subtle changes in liquid physical properties such as the dispersion state and magnetic properties of magnetic powder. found.

(Means for Solving the Problems) The present inventors have solved the above-mentioned drawbacks (as a result of various studies, by determining the optimum frequency for a certain specific liquid composition and coating speed, (1/1o to 1/l of the coercive force of the magnetic material) enables high random orientation treatment.In other words, the frequency (HM)/coating speed is he
(rIL/min) It was discovered that a magnetic recording medium with high characteristics could be manufactured by performing a random orientation process using an alternating current magnetic field generator that can be varied from L/10 to 1/1. 1. The present invention was achieved. .

Hereinafter, an apparatus implementing the method of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic diagram of an embodiment of a magnetic recording medium manufacturing apparatus to which the method of the present invention is applied. The long, strip-shaped non-magnetic support 2 wound around the delivery roll 1 is continuously transported in the direction of arrow A, and is wound around the take-up roll 6.

At a position close to the surface of the nonmagnetic support 20 to be transferred,
A coating device 3 is provided to apply magnetic liquid.

A frequency-variable AC magnetic field generator 4 is disposed downstream from the coating device 3 in the support transport direction A to apply a magnetic field to perform a random orientation process.

Further, a drying device 5 is provided on the downstream side.

In the above manufacturing apparatus, the magnetic particles of the magnetic liquid layered on the non-magnetic support 2 are randomly oriented in an undried state by the single frequency variable alternating current magnetic field generator 4. At this time, the frequency (Hz) generated by the variable frequency alternating current magnetic field generator 4 is
The absolute value is set to be variable in the range of 0.1 to 1 with respect to the traveling speed of the non-magnetic support 2 (the speed of passage through the magnetic field generator 4 (m/min)), and the applied The magnetic field strength of the alternating current magnetic field is set within the range of 0.1 to 1 of the coercive force of the magnetic material.

After the orientation treatment as described in 5 above, 5 then a drying device 5.
When passing through, the undried magnetic coating layer dries and solidifies, yielding a sheet-like magnetic recording medium.

By subsequently punching out this magnetic recording medium, a magnetic disk or the like can be formed.

The intensity of the magnetic field applied like the magnetic field generator 4 is kept within a certain range relative to the coercive force of the magnetic particles (magnetic material) in the magnetic liquid, and the frequency of the current that generates the alternating magnetic field is kept constant relative to the coating speed. By making it variable within a range, it is possible to easily achieve random orientation of the magnetic particles within a desired range even if there is some influence due to the characteristics of the coating liquid, such as the dispersion state or the magnetic properties of the magnetic particles. can. This is because the randomization of magnetic particles progresses effectively by applying an alternating magnetic field that is approximately equal to or smaller than the coercive force of the magnetic particles and has a strength of 1/10 or more, and in addition, the alternating magnetic field The mechanical influence of .

When the value of frequency (EI!)/application speed (m/min) is in the range of 0.1 to 1, there is no region where the orientation ratio (C3Q ratio) deteriorates extremely, and random orientation treatment is effective. This is because the orientation ratio can be brought close to approximately 1.

Note that the magnetic field application time is not particularly limited, and can be changed as appropriate depending on, for example, the magnetic field strength and the support traveling speed. In this specification, the orientation ratio (C3Q ratio) is expressed as the squareness ratio SQ in the longitudinal direction of the magnetic layer and the squareness ratio SQ perpendicular to it (C8Q upper/SQ/). .

Therefore, by using the variable frequency alternating current magnetic field generator 4 that implements the method of the present invention, the random orientation process can be easily set even when manufacturing various magnetic recording media, and magnetic recording media of stable quality can be produced. can be provided.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Polyethylene terephthalate (PF:T) with a thickness of 75 μm
) A magnetic liquid equivalent to a dry thickness of 2 μm is applied onto a non-magnetic support (K), and the orientation of the magnetic particles is randomized using a variable frequency alternating current magnetic field generator 4 installed downstream in the transfer direction. , drying, punching, and in the process of manufacturing magnetic disks.

The differences in the randomization of the magnetic particles when random orientation treatment was performed by changing the frequency to three different frequencies of 5 Hz, 50 Hz, and 100 Hz at coating speeds of 50 m/min and room/min, respectively, were compared to the results of each manufactured magnetic layer. It was investigated by measuring the orientation ratio (C3Q ratio).

Note that when the orientation ratio (SQ ratio) is 1, it indicates that the magnetic particles are completely randomized.

In this example, two types of liquids A having different liquid compositions are used.

B was used as a coating liquid. The compositions of the two types of liquids A and B are as shown in Table 11 and Table 2 below.

Table 1CA liquid) γ-B'e203 (Magnetic material coercive force 240Da)
400 weight tm polyurethane and Tuboran 3022)
60 weight 1 part vinyl chloride vinyl acetate copolymer (V
MCH) 40 parts by weight lecithin
6 parts by weight stearic acid
5 parts by weight carbon
30 parts by weight Methyl ethyl ketone soo parts by weight Methyl isobutyl ketone 200 parts by weight Cyclohexanone 200 parts by weight Table
2CB liquid) Co-containing r -Fe20B (Magnetic material coercive force 600 Yio 100 parts by weight Nitrocellulose
IO! Tsuboran 2304 for Yaribe polyurethane)
8 parts by weight polyisocyanate
8 parts by weight 0r203
2 parts by weight Carbon 2 parts by weight Stearic acid 1 part by weight Butyl stearate 1 part by weight Methyl ethyl ketone 300 parts by weight Orientation ratio (C3Q ratio) of a magnetic disk subjected to random orientation treatment using the VC1 frequency variable AC magnetic field generator as described above
The results of plotting the value against the magnetic field strength are shown in FIGS. 2, 3, 4, and 5. The second factor, FIG. 3, shows the results when the coating speed 9 is son/min, and the fourth factor, FIG. 5, shows the results when the coating speed is 100 m/min. From this result, for example, looking at the results for liquid A in Figure 2, it is clear that even at frequencies of 100 and 50 Hz, the magnetic field strength that provides the orientation ratio IK (completely randomized) is equal to the coercive force of the magnetic material (24
There are two points on both sides with 0·oe> in between, and if random orientation processing is performed at this magnetic field strength, a magnetic disk with an orientation ratio of 1 can be manufactured. However, even if the composition is the same, the optimal magnetic field strength point changes due to the influence of subtle changes in the dispersion state of the liquid, the magnetic properties of the magnetic powder, etc., and stable production is therefore not possible. Therefore, as is clear from the results for liquid A in Figure 2, by setting the optimum frequency to 5Hz, the magnetic field strength region where the orientation ratio is 1 becomes wider, and the magnetic field strength is set near the center of this magnetic field strength region. By performing the orientation treatment, high-quality magnetic disks can be stably manufactured. Furthermore, K as shown in FIG.

It is clear that as the coating speed r increases, the optimum frequency also increases for the same coating liquid.

Further, when liquid B was applied (FIGS. 3 and 5), although the optimum frequency was different from that of liquid A, it showed the same tendency as the result in the case of liquid A as described above. In this way, the optimum frequency changes depending on the composition of the liquid and the coating speed, but the value of the frequency (Hri/coating speed fcm/min) is usually 1/10 to 1/1/2.
It can be seen that if a random orientation process is performed using an alternating current magnetic field generator having a frequency variable range that allows up to 1, a high quality magnetic recording medium can be stably manufactured.

(Effects of the Invention) As described above, the method of the present invention variably sets the relationship between the magnetic field strength range, the common ridge frequency (Hz), and the coating speed within a specific range, so that the orientation ratio can be adjusted within the range. 1st year of junior high school
Since this state can be maintained continuously, stable random alignment processing can be performed. Therefore, according to the apparatus using the method of the present invention, it is easy to set up a good random orientation treatment, and it is possible to guarantee stable production of high-quality magnetic recording media.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a magnetic recording medium manufacturing apparatus using the method of the present invention, and FIGS. 2 to 5 are graphs of examples for explaining the present invention. 1... Delivery roll 2... Non-magnetic support 3...
・Coating device

Claims (1)

[Claims] In a method for producing a magnetic recording medium, a magnetic layer is provided by coating a magnetic liquid on a continuously running support, and an alternating current magnetic field is applied to the magnetic layer while it is not dry to perform a random orientation treatment. The magnetic field strength is 1/10 to 1 of the coercive force of the magnetic material.
/1, and the frequency (Hz)/coating speed (m/min) is 1/1 of the magnetic layer passing speed in the magnetic field.
A method for manufacturing a magnetic recording medium, characterized in that orientation treatment is performed in a variable range from 0 to 1/1.