JP2623897B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium having two magnetic layers for video.

2. Description of the Related Art In recent years, as the performance of magnetic recording media has increased, the number of magnetic layers
Layered video magnetic recording media are attracting attention.
For example, by providing a magnetic layer excellent in high-frequency electromagnetic conversion characteristics for high-density recording as an upper layer and providing a magnetic layer excellent in low-frequency electromagnetic conversion characteristics as compared to the upper layer as a lower layer, a conventional single layer cannot be obtained. Thus, a magnetic recording medium for video having excellent electromagnetic conversion characteristics from the low band to the high band can be obtained. 2
In a video magnetic recording medium having a layer structure, the thickness of the lower magnetic layer is larger than that of the upper magnetic layer, and is in the range of 0.5 to 4 μm. On the other hand, the coating thickness of the upper layer is preferably 0.1 to 0.5 μm.
If the film thickness is more than 5 μm, the characteristics in the low frequency band deteriorate,
The effect of the two layers is reduced. Further, when the thickness is smaller than 0.1 μm, the effect of the lower layer becomes strong, and thus the effect of the two layers also becomes small.

Such a two-layer magnetic recording medium for video usually has a lower magnetic layer coated on a support, oriented and dried, and then subjected to a surface smoothing treatment such as a calendar to form a magnetic layer as an upper layer thereon. A production method in which a layer is further applied, and orientation, drying, and surface smoothing treatments are performed. It is known that the lower layer and the upper layer are applied by a reverse coat, a gravure coat, a kiss coat, a blade coat, or the like. The method of manufacturing a magnetic recording medium as described above is described in, for example,
No. 17291 discloses this.

Further, a method of simultaneously coating two magnetic layers is disclosed in
63-88080.

However, Japanese Patent Publication No. 57-17291 does not disclose any method for producing a magnetic recording medium for video having an upper layer thickness of 0.1 to 0.5 μm to which the present invention is directed. In particular, when an extremely thin coating film having an upper layer thickness of 0.1 to 0.5 μm is to be uniformly formed on a lower-layered support, the above known coating methods such as gravure coating and reverse coating may not be possible. It has been found by the study of the present inventors.

Further, as disclosed in JP-A-63-88080,
The present inventors have found that in the simultaneous two-layer coating method, when a magnetic coating solution for high-density recording is applied as an upper layer, fine vertical streaks are generated on the coating film surface.

FIG. 2 shows a 14 μm-thick polyethylene terephthalate film as a support by the conventional simultaneous coating method using the magnetic coating solution shown in Table 1 as the upper layer and the magnetic coating solution shown in Table 2 as the lower layer. This is an example of the result of measuring the coating film surface with a three-dimensional surface roughness meter after applying it on the surface and performing a calendar treatment.

In the measurement results, only the portion of the three-dimensional graphics which is higher than the average value in the height direction is output in order to make the projections on the coating film surface easy to see. Fine vertical stripes having a pitch of about 50 μm are observed on the surface of the coating film in the running direction of the support. Further, the average surface roughness of the coating film surface in FIG. 2 was 15.8 nm. When the electromagnetic conversion characteristics were measured using an MII format deck, the video band output (7 MHz) was -2 dB relative to our standard tape, and the S / N ratio was -dB. From the above, it is apparent that fine vertical streaks on the surface of the coating film as shown in FIG. 2 significantly reduce electromagnetic conversion characteristics. The present inventors have investigated the cause of the generation of the fine vertical streaks and found that the cause is as follows.

The magnetic coating solution is unlikely to exist as primary particles due to the effect of magnetic force between the magnetic powder particles, and forms a three-dimensional network structure. When a shear is applied to this, a certain size is obtained. It is thought that it will be destroyed by the agglomerates you have. (Painting Engineering, Vol. 21, No. 10, pp. 475-479, 1986).

For example, a magnetic coating solution using a magnetic powder having a strong magnetic force such as an alloy magnetic powder and having a small average particle diameter in the major axis direction has a very strong cohesive force. It is considered to be present in the flowing coating solution on the order of μm. When this magnetic coating solution is applied to a support by the above-described coating method, the agglomerates are extruded from the slit of the conventional simultaneous two-layer coating device onto the lip surface. In this method, the lower layer and the upper layer simultaneously flow in the gap between the lip surface of the coating device and the support, so that the velocity gradient in the upper layer in the direction perpendicular to the running direction of the support decreases. As a result, the shear rate imparted to the upper layer magnetic coating liquid is reduced, the aggregates in the upper layer coating liquid cannot be broken, and the aggregates flow in the gaps, so that vertical streaks are generated. I understood.

Further, it was confirmed by an experiment that such fine vertical streaks appeared more remarkably when a magnetic coating solution using a magnetic powder having a strong magnetic force and a small average particle diameter in the major axis direction was applied.

Problems to be Solved by the Invention Magnetic recording media for video are in the direction of high density recording,
In particular, since a magnetic layer having a high magnetic force and an ultrafine magnetic powder such as an alloy magnetic powder is used as an upper layer of a video magnetic recording medium having a two-layered magnetic layer, fine vertical stripes on the coating film surface as described above are used. Is
The electromagnetic conversion characteristics such as video band output and S / N ratio were remarkably reduced, which was a fatal defect in product quality.

An object of the present invention is to provide an upper magnetic layer having a dry film thickness of 0.1 to 0.5.
An object of the present invention is to provide a method for producing a magnetic recording medium having a uniform film thickness and a very smooth coating surface in the production of a high-density magnetic recording medium for μm video.

Means for Solving the Problems In order to solve the above problems, a method for manufacturing a magnetic recording medium according to the present invention is to provide a magnetic layer containing an alloy magnetic powder on a support in advance, as a lower layer. Thickness 0.1
In the method for manufacturing a magnetic recording medium in which an upper layer having a thickness of about 0.5 μm is formed by coating, the second lip surface of the die is a curved surface, the slit side edge of the first lip is A, and the slit side edge of the second lip is B. At this time, the angle θ between the tangent at A and the tangent at B is 0 ° ≦ θ ≦ 45 °, the radius of curvature R of the second lip is 3 mm ≦ R ≦ 20 mm, and any part of the first lip is With a die configured not to cross from the tangent at
The upper layer is formed by coating.

Function The present invention has a structure in which the dried magnetic layer, which is the lower layer, is previously provided on the support, so that when the magnetic coating liquid for the upper layer is coated with a die, the conventional two-layer simultaneous coating method is used. In comparison, the velocity gradient of the magnetic coating solution for the upper layer flowing in the gap between the surface of the lower layer and the lip surface of the die in the direction perpendicular to the running direction of the support can be greatly increased. As a result, a high shear rate is given to the magnetic coating liquid for the upper layer, and the agglomerates are broken more finely, whereby the generation of fine vertical streaks on the coating film surface can be suppressed. Furthermore, by setting the radius of curvature of the second lip surface of the die to 3 to 20 mm, the second support of the lower layer and the die
Since a large surface pressure can be applied from the support with the lower layer to the magnetic coating solution for the upper layer flowing through the gap with the lip surface, the surface of the magnetic layer for the upper layer can be sufficiently smoothed, so that a very smooth coating can be achieved. A membrane surface is obtained.

Further, by setting the second lip radius of curvature as described above, a large surface pressure can be applied to the magnetic paint for the upper layer flowing in the gap between the lower layer surface and the lip surface of the die. Entrainment of air entrained in the support and unevenness of the film thickness in the width direction of the support can be suppressed, and a thin layer having a magnetic layer thickness of 0.1 to 0.5 μm as the upper layer can be uniformly formed. .

Example An example of the present invention will be specifically described below.
On a support made of polyethylene terephthalate having a thickness of 14 μm, a magnetic coating solution shown in Table 2 was applied as a lower layer by gravure coating so that the thickness in a dry state became 3 μm, and after orientation in the running direction of the support, Dried. After drying,
The surface of the magnetic layer was smoothed by a calender.

The magnetic paint was obtained by kneading and dispersion. Kneading is magnetic powder,
Solvent and binder are kneaded by a kneader for a predetermined time,
Thereafter, the remaining components were added to obtain a magnetic paint. Examples of the dispersion include a roll mill, a ball mill, and a kneader. The orientation magnetic field is 3000 Gauss. The drying temperature of the magnetic layer was 60 to 110 ° C., and the drying time was 40 to 120 sec. The surface roughness of the lower magnetic layer after the calendering treatment is in the range of 4 to 10 nm. If the value of the surface roughness is larger than this, the surface roughness of the lower layer affects the upper layer, the surface roughness of the upper layer becomes worse, and the electromagnetic conversion characteristics in the high range are reduced.

FIG. 1 shows a method of applying the upper layer of the magnetic coating liquid 7 for the upper layer on the support 8 provided with the lower layer 9 by using the die 5. The cross section of the tip of the second lip 2 is a curved surface, and its radius of curvature R is 3 to 20 mm. The optimum radius of curvature is selected according to the conditions of the viscosity of the magnetic coating solution, the coating speed, the coating film thickness, and the support tension. The thickness of the first lip 1 and the second lip 2 is in the range of 2 to 10 mm. When the second lip surface of the die is a curved surface and the slit-side edge of the first lip is A and the slit-side edge of the second lip is B, the tangent to A and B
Is 0 ° ≦ θ ≦ 45 °. Furthermore, it is arranged that no part of the first lip of the die extends beyond the tangent at A in the direction of the support.

By using cemented carbide as the material of the two lips, the straightness and flatness of the lip can be finished on the order of several μm, and the outlet of the second lip seen when processing stainless steel or the like. It is possible to prevent edge burrs and sagging from occurring at the ends. As a result, even when the thin layer coating was performed, there was no thickness unevenness in the width direction, and there was no vertical streak on the coating film surface due to edge burrs or sagging, and good coating was possible.

The manifold 3 penetrates in the coating width direction of the coating device. The manifold may have a circular or semi-circular cross-sectional shape. The gap of the slit 4 is usually set to 0.1 to 0.5 mm, and the length of the slit in the width direction is almost the same as the application width. The slit length from the manifold to the slit outlet is set according to the application conditions such as the viscosity in consideration of the thixotropic property of the application liquid and the amount of discharge from the application device.
It is 20-100 mm long.

The shape of the tip of the first lip is a curved surface in FIG. 1, but may be a flat surface or a polygonal surface.

A guide roll (not shown) provided on the upstream side of the first lip so that the angle of entry of the support 8 with respect to the die nozzle is substantially parallel to the tangent line X at the point B of the second lip shown in FIG. Is adjusted by Further, the angle at which the support 8 emerges from the coating apparatus is determined by the tangent line Y shown in FIG.
Is adjusted by a guide roll (not shown) provided downstream of the second lip so as to be substantially parallel to the second lip.

The amount of the magnetic coating liquid 7 for the upper layer is continuously supplied into the manifold 3 by the pump 6 in an amount corresponding to the amount applied to the support, and is pushed out to the slit 4 by the liquid pressure in the manifold 3.

As described above, agglomerates of magnetic powder particles are present in the upper magnetic coating liquid 7 extruded from the slits 4. However, by setting the angle of the support with respect to the coating device shown in FIG. 1 as described above, the gap between the second lip surface and the support 8 through which the magnetic paint for the upper layer flows is about 1 to 1.
It is kept constant along the second lip surface in the range of 6 μm. The size of this gap is very small as compared with the size of the agglomerate, and the size of the upper magnetic coating material 7 is 10 ⁵ to 10 ⁶ (1/1).
Since a high shear rate on the order of sec) is continuously applied, the agglomerates are finely broken, the coating film surface is smoothed, and the generation of fine vertical streaks on the coating film surface is suppressed.

Example 1 Using the above-mentioned coating method, a magnetic coating solution shown in Table 1 as a magnetic coating solution for the upper layer was applied to the surface of the magnetic layer provided with the lower layer having a thickness of 3 μm as described above. The coating speed is 100m / min.

The magnetic coating liquid was discharged from the die so that the thickness of the upper layer in a dry state was 0.5 μm. Four types of die having a second lip curvature radius of 2, 3, 20, and 21 mm were used. The tension in the coating head of the support is 300 g
/ cm was applied to the upper layer magnetic coating solution.

After coating, the support was oriented in the running direction and then dried. After drying, the surface of the magnetic layer was smoothed by a calender and slit to a predetermined width to prepare a magnetic recording medium. The orientation magnetic field was 3000 Gauss and the drying temperature of the magnetic layer was 6
0-110 ° C and the drying time is 40-120 sec.

As a result of preparing a magnetic recording medium by the above method, when the radius of curvature of the second lip was 2 mm, the magnetic coating liquid coming out of the slit spilled to the first lip side, and the coating film thickness became uneven. When the radius of curvature of the second lip was 21 mm, air entrained in the support was entrained in the coating liquid, and the coating film was lost and could not be coated. The second lip radius of curvature is 3
And those coated with a 20 mm die could be uniformly coated with a film thickness of 0.5 μm.

FIG. 3 (a) (R = 3m) shows the results of measuring the coating surface of a magnetic recording medium prepared using a die having a second lip curvature radius of 3 and 20 mm with a three-dimensional surface roughness meter.
m) and FIG. 3 (b) (R = 20 mm). Fine vertical streaks (FIG. 2) observed on the surface of the coating film when the simultaneous two-layer coating device was used were not generated at all, and a smooth coating film surface was obtained.

Further, the electromagnetic conversion characteristics of a magnetic recording medium prepared by using the method for manufacturing a magnetic recording medium according to the present embodiment and a magnetic recording medium prepared by a conventional simultaneous two-layer coating apparatus were compared and evaluated. For evaluation, the output and the S / N ratio at a frequency of 7 MHz in the video band were measured using an MII format deck. Third result
It is shown in the table.

For measurement of the electromagnetic conversion characteristics, an MII tape prepared by us was used as a reference tape for easy comparison. Table 3 also shows the average surface roughness measured with a three-dimensional surface roughness meter. The tape produced by the method for producing a magnetic recording medium according to the present invention, that is, the tape produced with the die having the second lip radius of curvature R = 3 and 20 mm, has a very smooth coating film surface. As compared with the tape prepared in the above item, the average surface roughness was smaller, the reproduction output and the S / N ratio were extremely excellent, and it was found that the effect of the present invention was remarkable.

Example 2 Using the above coating method, a magnetic coating solution shown in Table 1 was applied as a magnetic coating solution for the upper layer to the surface of the magnetic layer provided with the lower layer having a thickness of 3 μm as described above. The coating speed is 100m / min.

The upper layer was discharged onto the magnetic coating liquid so that the film thickness in a dry state was 0.1 μm. Four types of die having a second lip curvature radius of 2, 3, 20, and 21 mm were used. The tension of the support in the coating head was 400 g / cm, and the upper layer magnetic coating solution was applied. A magnetic recording medium was prepared in the same manner as in Example 1 except for the manufacturing method after the application of the upper layer. When the radius of curvature of the second lip was 2 mm, the magnetic coating solution that had come out of the slit spilled to the first lip side, and the coating film thickness became uneven. When the radius of curvature of the second lip was 21 mm, air entrained in the support was caught in the coating solution, and the coating film came off, preventing application. When applied with a die having a second lip radius of curvature of 3 or 20 mm, the film pressure is
The coating could be applied uniformly at 0.1 μm.

Further, the electromagnetic conversion characteristics of a magnetic recording medium prepared by using the method for manufacturing a magnetic recording medium according to the present embodiment and a magnetic recording medium prepared by a conventional simultaneous two-layer coating apparatus were compared and evaluated in the same manner as in Example 1. The results are shown in Table 4.

For measurement of the electromagnetic conversion characteristics, an MII tape prepared by us was used as a reference tape for easy comparison. Table 4 also shows the average surface roughness measured by a three-dimensional surface roughness meter. The tape produced by the method for producing a magnetic recording medium according to the present invention, that is, the one in which the upper layer is applied and formed by a die of R = 3 and 20 mm, has an average surface roughness higher than that of the tape produced by applying the conventional coating apparatus. Is small, playback output and S /
The levels of both N ratios were remarkably excellent, and it was found that the effect of the present invention was remarkable.

Comparative Example A magnetic coating solution shown in Table 1 was used as a magnetic coating solution for the upper layer in a dry film thickness of 0.5 μm by a simultaneous two-layer coating device as a conventional example.
m, a magnetic coating solution shown in Table 2 as a magnetic coating solution for the lower layer was applied to the support at a dry film thickness of 3 μm.

The coating solution was applied on a 14 μm-thick polyethylene terephthalate film as a support at a coating speed of 100 m / min, and then calendered and slit to prepare a tape. FIG. 2 shows the results of measuring the coating surface of the tape with a three-dimensional surface roughness meter. In addition, output of frequency 7MHz and S /
Tables 3 and 4 show the electromagnetic conversion characteristics such as the N ratio. Tables 3 and 4 show the average surface roughness frequency of our standard tape of 7M.
Hz output and S / N are also shown.

Effects of the Invention As described above, according to the present invention, in the production of a magnetic recording medium having a magnetic layer having a two-layer structure, the magnetic force is very high, and the average particle diameter in the major axis direction is very small. With respect to a strong magnetic coating solution, the surface of the upper coating film can be manufactured to be very smooth and uniform with a film thickness of 0.1 to 0.5 μm. As a result, the product quality of a high-density magnetic recording medium having a two-layer structure can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a method for manufacturing a magnetic recording medium according to the present invention, and FIGS. 2 and 3 are explanatory diagrams showing the results of measuring the surface of a coating film with a three-dimensional surface roughness meter. 1 ... first lip, 6 ... pump, 2 ... second lip,
7 ... magnetic coating solution for upper layer, 3 ... manifold, 8 ...
Support, 4 ... Slit, 9 ... Lower layer, 5 ... Die.

Claims (6)

(57) [Claims] A magnetic layer is provided as a lower layer on a support in advance,
A method for manufacturing a magnetic recording medium, wherein a magnetic layer having a thickness of 0.1 to 0.5 μm in a dry state is coated and formed as an upper layer, wherein the second lip surface of the die is a curved surface, and the slit-side edge of the first lip is A When the slit side edge of the second lip is B, the angle θ between the tangent at A and the tangent at B is 0 ° ≦ θ ≦ 45 °, and the radius of curvature R of the second lip is 3 mm ≦ R ≦ With a die which is 20 mm and is constructed so that no part of the first lip extends beyond the tangent at A in the direction of the support,
A method for manufacturing a magnetic recording medium, comprising forming an upper layer by coating. 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the upper layer is a magnetic layer containing an alloy magnetic powder. 3. The method according to claim 1, wherein the upper layer is a magnetic layer containing iron oxide magnetic powder. 4. The method according to claim 1, wherein the upper layer is a magnetic layer containing barium ferrite. 5. The method of manufacturing a magnetic recording medium according to claim 1, wherein the upper layer is a magnetic layer containing iron nitride. 6. The method according to claim 1, wherein the upper layer is a magnetic layer containing iron carbide.