JPH0640388B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a magnetic recording medium, and particularly to a magnetic recording medium suitable for use in producing a coated disc medium such as a floppy disc. The present invention relates to a manufacturing method of.

(Prior Art) Generally, a magnetic recording medium such as a magnetic disk or a magnetic tape is strongly transferred to a binder dissolved in a solvent on a belt-shaped non-magnetic support while continuously transferring it in the longitudinal direction. It is manufactured by coating a magnetic liquid in which magnetic fine particles are dispersed, drying and solidifying the magnetic liquid, and then punching or cutting the support.

However, in the manufacture of a magnetic disk, if ferromagnetic particles are arrayed in a specific direction during manufacture and anisotropy occurs in the magnetic recording medium, anisotropy also occurs in magnetic characteristics and electric characteristics in various directions. For example, when the magnetic particles are arranged along the direction in which the magnetic liquid is applied (that is, the direction in which the non-magnetic support is transported), in particular, the magnetic head does not scan linearly as in the case of a magnetic disk, but the circumference of the magnetic head. When scanning concentrically in one direction, the reproduction output signal level in this coating direction becomes higher than that in the other direction, and as a result, the reproduction output signal level read from the magnetic disk follows the rotation of the disk. Change (this phenomenon is commonly referred to as modification). 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 influence, and the state in which orientation treatment is performed in a specific direction occurs at a high rate. Therefore, when a magnetic disk or the like is conventionally manufactured, in order to solve the above-mentioned problem that the magnetic particles have a linear directionality due to the flow orientation at the time of coating the magnetic liquid, the magnetic liquid is not dried. A method of making the orientation of magnetic particles disordered (randomized) by applying a magnetic field is adopted. As described above, as a method for applying a magnetic field while the magnetic liquid is not dried, Japanese Patent Application Laid-Open No.
A method of applying an alternating magnetic field as disclosed in Japanese Patent Publication No. 57-198545 is known.

(Problems to be Solved by the Invention) However, when the above-mentioned random alignment treatment by an alternating magnetic field is applied to the method for manufacturing a magnetic recording medium, the liquid composition and the coating speed are affected, and when these are changed, the random alignment treatment is successful. It turned out not to go. In addition, even with liquids of the same composition, the magnetic field conditions for complete randomization may change due to subtle changes in the dispersion state, magnetic properties of the magnetic powder, etc., and stable random orientation processing may not be possible. found.

Then, looking at these causes, it was found that, in the first problem, the optimum frequency exists for the liquid composition and the coating speed (support traveling speed).
That is, if the frequency is too high, the movement of the magnetic body cannot follow the change of the magnetic field, and the magnetic body is aligned in the direction perpendicular to the direction of the applied magnetic field (horizontal direction with respect to the magnetic field application in the longitudinal direction), On the contrary, it was found that if the frequency is too low, the magnetic materials are aligned in the magnetic field application direction. In addition, in the second problem, since it is randomized at the balance point between the liquid composition and the magnetic field strength, it is susceptible to subtle changes in liquid properties such as the dispersion state and the magnetic properties of the magnetic powder. found.

(Means for Solving Problems) As a result of various investigations for solving the above-mentioned drawbacks, the present inventors determined an optimum frequency for a specific liquid composition and coating speed, and It was found that a high random orientation treatment is possible with (1/10 to 1/1 of the coercive force of the magnetic material). That is, the frequency is the frequency (Hz) / coating speed (m / min) relative to the magnetic layer passing speed in the magnetic field.
The present invention has been achieved by finding that a magnetic recording medium with high characteristics can be manufactured by performing a random orientation treatment using an AC magnetic field generator that is variable from 1/10 to 1/1.

An apparatus for carrying out the method of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic view 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 transferred in the direction of arrow A and wound around the winding roll 6. A coating device 3 is arranged at a position close to the surface of the non-magnetic support 2 to be transferred, and coats the magnetic liquid.

A frequency variable AC magnetic field generator 4 for applying a magnetic field to perform a random orientation treatment is disposed downstream of the coating device 3 in the support transfer direction A, and a dryer 5 is disposed further downstream. It is set up.

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

After being oriented as described above, the drying device 5 is then used.
After passing through, the undried magnetic coating layer is dried and solidified to obtain a sheet-shaped magnetic recording medium. A magnetic disk or the like can be formed by punching this magnetic recording medium thereafter.

The magnetic field strength applied as in the magnetic field generator 4 is within a certain range with respect to the coercive force of the magnetic particles (magnetic material) in the magnetic liquid, and the frequency of the current for generating the alternating magnetic field is constant with respect to the coating speed. By making the range variable, the random orientation of the magnetic particles can be easily performed within a desired range even if the coating liquid has some influence due to various properties such as the dispersion state and the magnetic properties of the magnetic particles. it can. This is because the randomization of the magnetic particles effectively progresses by applying an alternating magnetic field having a strength approximately equal to or smaller than the coercive force of the magnetic particles and 1/10 or more, The mechanical effect of the alternating magnetic field on the magnetic particles depends on the relationship between the frequency and the passage speed in the magnetic field (coating speed), and the following equation set by the present inventors: frequency (Hz) / coating speed (m)
/ Min) value is in the range of 0.1 to 1, the orientation ratio (SQ
This is because there is no region where the ratio) is extremely deteriorated, the random alignment treatment is effectively performed, and the alignment ratio can be brought close to 1.

The magnetic field application time is not particularly limited, and can be appropriately changed depending on, for example, the magnetic field strength and the support traveling speed. In the present specification, the orientation ratio (SQ ratio) is indicated by the ratio (SQ⊥ / SQ) between the squareness ratio SQ in the longitudinal direction of the magnetic layer and the squareness ratio SQ⊥ orthogonal thereto.

Therefore, by using the frequency-variable AC magnetic field generator 4 which has been subjected to the method of the present invention, the random orientation process can be easily set even when various magnetic recording media are manufactured, and the magnetic recording media of stable quality can be obtained. Can be provided.

〔Example〕

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

A non-magnetic support made of polyethylene terephthalate (PET) with a thickness of 75 μm is coated with a magnetic liquid having a dry thickness of 2 μm, and magnetized by a frequency variable AC magnetic field generator 4 arranged downstream of the transfer direction. In the process of randomizing the orientation of the particles, drying, punching, and manufacturing a magnetic disk, the coating speed is 50 m / min, 100 m / min.
Frequency of 5Hz, 50Hz, 100Hz at each of 3 minutes
The difference in randomization of the magnetic particles in the case of performing the random orientation treatment by changing the above was investigated by measuring the orientation ratio (SQ ratio) of each magnetic layer produced. The orientation ratio (SQ ratio) indicates that when the value is 1, the magnetic particles are completely randomized.

In this example, two types of liquids A and B having different liquid compositions were used as coating liquids. The compositions of the two kinds of liquids A and B are shown in Tables 1 and 2 below.

As described above, the results of plotting the orientation ratio (SQ ratio) of the magnetic disk subjected to the random orientation treatment by the frequency variable AC magnetic field generator with respect to the magnetic field strength are shown in FIGS. 2, 3, 4 and 5. Shown in. Figures 2 and 3 show a coating speed of 50 m / min, and Figures 4 and 5 show a coating speed of 10
It shows the result of 0 m / min. From this result, for example, if you look at the result of liquid A in Fig. 2, frequencies 100 and 50H
Even in z, there are two magnetic field strengths on the both sides of the magnetic material coercive force (240 Oe) that surely has an orientation ratio of 1 (completely randomized). If random orientation processing is performed with this magnetic field strength It is possible to manufacture a magnetic disk having an orientation ratio of ≈1. However, even with the same composition, the optimum magnetic field strength point changes due to subtle changes in the dispersion state of the liquid, the magnetic properties of the magnetic powder, etc., and stable manufacture is not possible.
Therefore, as is clear from the results of solution A in FIG.
By setting the optimum frequency to 5 Hz, the magnetic field strength region where the orientation ratio ≈ 1 becomes wider. By setting the magnetic field strength near the center of this magnetic field strength region and performing the orientation process, a stable, high-quality magnetic disk can be obtained. Can be manufactured. Further, as shown in FIG. 4, it is clear that the optimum frequency increases with the same coating liquid as the coating speed increases.

Further, when the solution B was applied (FIGS. 3 and 5), the optimum frequency was different from that of the solution A, but the same tendency as the result of the case of the solution A was shown. In this way, the optimum frequency changes depending on the composition of the liquid and the coating speed, but the frequency variable range where the value of normal frequency (Hz) / coating speed (m / min) can be set to 1/10 to 1/1. It is understood that a high quality magnetic recording medium can be stably manufactured by performing the random orientation treatment using the AC magnetic field generator having the above.

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

[Brief description of drawings]

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 4 ... Frequency variable AC magnetic field generator 5 ... Drying device, 6 ... Winding roll

Claims (1)

[Claims] 1. A method for producing a magnetic recording medium, wherein a magnetic liquid is applied on a continuously running support to form a magnetic layer, and an alternating magnetic field is applied to the magnetic layer while the magnetic layer is undried to perform a random orientation treatment. , The magnetic field strength of the applied AC magnetic field is
1/10 to 1/1, and frequency is 1 / frequency (Hz) / coating speed (m / min) with respect to the magnetic layer passing speed in the magnetic field.
A method for manufacturing a magnetic recording medium, which comprises subjecting an orientation treatment to a range variable from 10 to 1/1.