JPS61177632A - Production of magnetic recording film coated medium - Google Patents

Abstract

PURPOSE:To attain sufficient vertical orientation on the surface of a medium by performing AC degaussing just after vertical orientation to erase a demagnetizing field Hd which causes orientation break and preventing a vertically oriented and magnetized low-viscosity coated liquid from going out of the magnetic field to rotate particles with their own demagnetizing field Hd due to surface magnetic charge. CONSTITUTION:A magnetic recording film coated medium has double-layered constitution, and single magnetic domain particles having uniaxial magnetic anisotropy are oriented vertically in the outer layer and are orientated lenghthwise in the deep layer. This coated film passes successively between vertical magnetic field orienting electromagnets 11 and 12 of a coated film line 7. The gap part between magnetic poles of electromagnets 11 and 12 is constituted of an AC magnetic field orienting part 3 and an AC degaussing part 4 excited by AC power sources 21 and 22. AC degaussing is performed by the degaussing part 4 just after vertical orientation in the orienting part 3 to erase the demagnetizing field Hd which causes orientation break. Thus, the vertically oriented low-viscosity paint is prevented from going out of the magnetic field to rotate particles with their own demagnetizing field Hd due to surface magnetic charge, thereby attaining sufficient vertical orientation on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a method of manufacturing high density, broadband magnetic recording coated media.

[Prior Art] Conventionally, magnetic recording is performed using a combination of a ring head and a longitudinally oriented acicular particle coating medium, and long wavelength and medium wavelength components are efficiently recorded in the longitudinal direction.

However, the short wavelength component that accompanies higher recording densities is actually recorded on the surface layer in a perpendicular mode residual magnetization pattern using a small amount of remaining perpendicularly oriented component. According to recent analysis, when comparing three types of coating media: longitudinally oriented, vertically oriented, and isotropic, the long wavelength reproduction output is 1 isotropic>longitudinal perpendicular, and D5o, which is an index of high density.
It is shown that the order is vertical, isotropic, and longitudinal. (IEICE study group material MR83-41
, 1983) Therefore, for the same coating medium, the long wavelength output and D5
To achieve broadband characteristics with large o values, the surface layer should be oriented vertically and short wavelength components should be recorded using a vertical pattern, while the deep layers should be oriented longitudinally and long wavelength components should be recorded using a longitudinal pattern. . Furthermore, this configuration allows efficient recording as a substantially isotropic medium by using both the vertical and longitudinal layers along the arc-shaped magnetic field of the ring head.

The original design of such a two-layer tape was not based on the clear analysis mentioned above, but it was based on the general idea described in the specification of U.S. Pat. No. 3,052,567 (1962). It is publicly known. However, the high-density, wide-area tape according to this patent has not been achieved using a vertical alignment method that simply changes the conventional longitudinal magnetic field alignment method to vertical.
This is because a vertical layer with a smooth and high vertical squareness ratio SQR could not be formed. D. (ii) In order to improve the long-wavelength recording efficiency when using a high-density narrow gap recording/reproducing ring head, it is possible to reduce the thickness of the vertically aligned surface layer corresponding to the distance from the head to the first layer. .

It is an object of the present invention to provide a method for producing a coating medium having a two-layer structure to about magnetic fields.

[Means for solving the problem] and "effects" This is because in the conventional perpendicular alignment caused by a DC magnetic field, the particles are reoriented and rotated by the magnetic field Hd on two surfaces, and this phenomenon is particularly
noticeable on large surfaces.

In a previous application (Japanese Patent Application No. 59-057106), the present inventor conducted AC demagnetization immediately after vertical alignment to eliminate Hd, which is the cause of alignment return.
), this problem was solved.

(See Figure 1) Regarding surface roughness that occurs during vertical magnetic field orientation, which was another problem, if the magnetic field orientation conditions are kept modest and the degree of orientation is accumulated through repeated orientation, the degree of surface roughness that appears will still vary. This problem was solved by smoothing using surface tension during the non-magnetic field period during orientation. By this method, a vertical single-layer coating film could be realized in the previous application, and by incorporating this into the vertical layer of the two-layer structure of the present invention, the above-mentioned objective (i) is achieved. It is.

Next, the purpose (to make a thin vertical layer of IO) is that in the above-mentioned U.S. patent, the two-layer coating process is oriented longitudinally and vertically, so due to the coating thickness limit of current coating technology, It is difficult to thin the vertical layers below 1.5 microns.

In this invention, in the second coating step, first, the entire thickness of the coating liquid is vertically oriented, and second, the viscosity of the surface layer of the coating liquid is made higher than that of the deep layer. (Figure 2A) The time constant τr of orientation rotation of particles in a viscous fluid is relative to the time (interval) Δt at which the viscosity rapidly increases.

If the relationship τ (surface layer) Δt) τr (deep layer) is passed through a longitudinally oriented magnetic field, only the deep layer will change in the longitudinal direction. If we find the optimal conditions for the vertical direction, we can make the vertical surface layer thin ((
0.1 to 0.5 micron) can be left (created) and the desired two-layer structure can be realized.

Ru. Figure 1 shows a coating production line. The low-viscosity coating liquid first passes sequentially between the magnetic poles of electromagnets (11, 12) for vertical magnetic field alignment. The magnetic pole gap of the electromagnet excited by the AC power source (21, 22) of f hertz (50 or 60) is
It consists of an AC magnetic field perpendicular orientation section (3) and an AC demagnetization section (4). Vertical alignment magnetic field.

The value is sufficiently large compared to the coercive force Hc of the magnetic particles, Hd of the coating liquid, local magnetic field of interaction between particles, etc. In this example, the maximum value is set to 5 Oersteds. The shape of the magnetic poles in the AC demagnetization section is such that the magnetic pole gap gradually expands symmetrically with respect to the coating surface.If the direction of travel of the coating film is X and the speed is V, then the shape of the expansion (AC demagnetization The distance ΔXacL) is determined as follows.

The value of ΔXacL is determined from the following AC demagnetization conditions.

f x (X'-x')/v > (Number of AC degaussing cycles required = 5, then a Xa (1 = X'-X
"=04m. The vertically oriented particle separation ΔXor is. Since the particles have anisotropic dispersion, the actual value of A is 1, but for convenience, in Figure 3, a Xor = X'c - X'
shall be.

Next, in order to smooth the surface roughness caused by vertical magnetic field orientation, the first
Smoothing periods c', cl' in the absence of magnetic field shown in the process shown in the figure
put The time interval is determined by the time constant of the smoothed viscous flow, and is approximately a few tenths of a second.

The distance is several percent centimeters. Orientation (A) - Demagnetization (B) - Smoothing (C) in the process to obtain the required 5QRL
The required number of repetitions of the set was 1 to 5 times, and in this example, 2 times.

The viscosity of the surface layer is due to evaporation of the solvent from the surface, as shown in Figure 2 (
As shown in A), the depth is greater, but in order to make the difference more noticeable, infrared rays (5) are irradiated for a short time after the process ABCABC. (D) As a result, only the thin surface layer has a higher temperature and therefore solvent evaporation rate.

Significant differences in viscosity and therefore "r:r" can be produced between the two layers, as shown in FIG. 2B.

The amount of infrared irradiation is such that the Tr (front) of the surface layer (thinness) is Tr (front) > 4t > r (deep).

Decide on time etc. Also, when r (depth) satisfies the above conditions,
Conventional tape manufacturing processes such as calendering and curing follow, but are well known and will therefore be omitted.

Figure 1 (A') (A") (B") corresponding to each process
) (C”) (D) (E) shows the particle orientation and spin direction at that time.

Surface magnetic charge 9 Surface roughness and thickness of each coating layer are shown.

(A') (A") shows the state at the phase of the maximum value of the alternating magnetic field.

The orientation state of the completed tape according to the present invention is shown in FIG. 9E, which shows the longitudinal orientation of the surface vertical orientation layer. In reality, the change in r in the thickness direction is continuous, although it is rapid.9
There is a continuous intermediate transition layer between both alignment layers, but its presence would rather serve to make the wavelength characteristics monotonic.

What is the most important and delicate technique in this manufacturing method?

By preventing non-uniformity in the thickness of the vertical surface layer, which causes media noise, it is possible to increase the viscosity of the surface layer (D
) and the process of longitudinal direction (E) to prevent convection of the coating liquid. Shortening the distance between (D) and (B), setting the irradiation intensity for 1 hour and 2 ventilation conditions so that the viscosity of the surface layer rises rapidly without causing roughness due to rapid evaporation, 2 setting the surface layer to be thin, etc. The key is to make sure that there is no time for convection to occur, and that it is difficult for it to occur.

High-power metal iron is used as the magnetic particles in the coating.

The long axis size is 0.1 micron to reduce media noise, and the axial ratio is 3/1, like a grain of rice, and Hc is 940.
06 is used. I made it into rice grains.

This is because if the grains are extremely acicular, the vertically oriented grains will easily collapse in the plane during calendering, and the Hc will become large, requiring the use of a technically difficult sendust head instead of ferrite. As for high-density recording, since it is two-surface perpendicular recording, it can be sufficiently achieved even if Hc is not so high. The manufacturing method for the metal coating liquid is the same as that for conventional longitudinal tape and is well known, so the description will be omitted.

[Embodiment 2, the embodiment button of claim (3) will be described. In configuring the two layers of this invention,
Effective thinning of the vertical surface layer can also be achieved with a two-layer coating process. That is, by using a two-layer coating and using a material with a lower Hc (for example, acicular 7-Fe2C) of 400 oersteds as the deep magnetic material, the recording magnetic field region of the ring head can be deep. Therefore, the long wavelength longitudinal recording efficiency can be effectively improved in the same way as when the surface layer is made thinner. The manufacturing method is based on the conventional longitudinal two-layer coating medium, in which a longitudinally oriented, low coercive force deep layer is first formed, and then a surface layer is formed with a coating liquid of rice granular iron particles (Hc ~ 900 Oe). The vertical alignment of the surface layer is performed by the method described above.

The advantage of this example is that the accuracy of surface layer thickness control can be increased (9), but the problem (2) of effective thinness of the surface layer (long wavelength efficiency) is also alleviated by the advancement of thin coating technology and the combination of a wide gap gutter for deep layers. will be done.

[Example-3] In Examples-1 and 2.

Although the vertical alignment magnetic field and the A-C demagnetizing magnetic field were generated using an AC power source and an electromagnet, they can be replaced with a set of permanent magnets. Figure 4 Ck) shows the magnetic field distribution.
(B) shows the arrangement of the permanent magnets.

The overall line is that of FIG. 1 with this set of permanent magnets replacing the AC electromagnets.

The vertical alignment part in Examples 1 and 2 was AC alignment because it conveniently used the same electromagnet as for the primary AC demagnetization, but when using permanent magnets, a C-shaped soft iron yoke (
9) forms a closed magnetic circuit.

The orientation magnetic field interval ΔXor is ■=2M/sec on the mass production line
Assuming that, ΔXor2 is set to 0.2 M. In general, electromagnets that use AC current are convenient for small prototype applicators (V ~ 0.2 M/,), but for mass production lines, Joule heat removal and electricity costs are issues, so it is necessary to use permanent magnets. Magnetic methods are advantageous.

The AC demagnetization section includes several (for example, 5) permanent magnet pairs (8,
8, 8, 8, . . . ) were installed in reverse order in order to create a magnetic field gradient.

As for the AC demagnetization part distance (Xad), there is no power frequency restriction, and intra-particle spin reversal makes it difficult to generate a very fast magnetic field in a finite magnetic pole gap (3 to 5 mm), so in the end, AXad w O , 2M.

The rest is the same as in Example-1 except that the smoothing processes c', c'' and the distances corresponding to the longitudinal direction time intervals t are respectively increased in proportion to V.

[Effect of the invention] In devising a conventional two-layer coating film with vertical orientation on the surface layer and longitudinal orientation on the deep layer for the purpose of high density and wide band expansion,
High S surface layer required to achieve high density perpendicular recording
What is QR and surface smoothness that reduces spacing loss?
Incorporating the vertical orientation-AC demagnetization-smoothing method,
It became possible for the first time to reduce Hd to zero on the most important surface52 by solving surface roughness. It is also possible to make this vertical surface layer thinner to increase the efficiency of recording long and medium wavelength components into the long and deep layers. This was achieved by changing the deep layer to a longitudinal direction.

For audio analog recording tapes that require recording in a wide wavelength range, video tapes that also include audio analog tracks, there is a strong demand for higher density (miniaturization) and wider band fidelity, so the contribution of this invention is significant. It is.
It is also similarly effective for the VH8-HiPi method of audio deep F'M recording.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a manufacturing line showing magnets etc. in a side view. Lower row (A') (A") is AC vertical magnetic field orientation. (The mark is AC demagnetization, (C") is smoothing, (D) is surface layer viscosity increase by infrared evaporation method, (E) is longitudinal orientation. The state of the coating liquid in each process is shown in Figure 2. Figure 2 shows the temporal changes in the viscosity of the coating liquid at the surface and deep layers '/ (A) and the particle orientation rotation time constant 'r: r (B). Graph (A) of the magnetic field distribution of the vertical alignment part and AC demagnetization part using magnets (A) and the magnet arrangement diagram (B) 011 and 12 are the magnetic poles of the AC electromagnet, 3 is the perpendicular thereof, and 9 is the yoke. 81 Yuan 144 Shu Hyaku Person 10, 1, 2 + can 2nd area Sai 3 Yoshi 4 Figure H (koe) 8pJl, ``6''

Claims (3)

[Claims] (1) In a magnetic recording coating medium with a two-layer structure in which single-domain grains with uniaxial magnetic anisotropy are vertically oriented in the surface layer and longitudinally oriented in the deep layer, the perpendicular magnetic field orientation treatment is performed by alternating current demagnetization. 1. A method for producing a magnetic recording coated medium, comprising: immediately after vertical magnetic field orientation, and combining this with a longitudinal magnetic field orientation treatment to form two layers. (2) A method for manufacturing a magnetic recording coated medium according to claim (1), wherein the magnetic field orientation treatment of the two-layer structure is carried out as follows. First, the entire thickness of the coating liquid is subjected to vertical magnetic field alignment treatment, and then, in the process of increasing the viscosity of the coating liquid while maintaining a high viscosity gradient on the surface layer side, the rotation time constant τ_r (table) and τ of particles in the surface layer and deep layer are calculated.
τ_r (table) ≫
At the time when the relationship Δt≫τ_r (depth) is satisfied, longitudinal magnetic field processing is performed. (3) In the magnetic field orientation treatment of the two-layer structure, first the longitudinal orientation,
A method for producing a magnetic recording coated medium according to claim 1, wherein a coating liquid for a surface layer is layered on a deep layer that has been calendered and hardened, and the coating liquid is vertically oriented.