JPH0829286B2 - Coating device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating device for a magnetic recording medium used as a magnetic tape or a floppy disk, and more particularly to a coating device for simultaneously coating two layers.

2. Description of the Related Art In recent years, as the performance of magnetic recording media has increased, multi-layered magnetic layers have attracted attention. For example, by providing a magnetic layer excellent in high-frequency electromagnetic conversion characteristics for high-density recording as an upper layer and a magnetic layer having a lower electromagnetic conversion characteristic than the upper layer as a lower layer, it has not been possible to obtain a conventional single layer. Excellent electromagnetic conversion characteristics can be realized. Furthermore, in order to improve the adhesion between the magnetic layer and the support made of a plastic film,
A multilayer structure of a magnetic recording medium is being advanced, such as an anchor layer provided between a magnetic layer and a support.

It is desired that such a multi-layer magnetic recording medium be manufactured by coating and drying once. For a coating apparatus for a multi-layer magnetic recording medium, see, for example, Japanese Patent Laid-Open No. 63-88080.
It is disclosed in Japanese Patent Publication No.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, it has been found by the study of the present inventors that fine vertical stripes are generated when a magnetic coating liquid for high-density recording is applied by the conventional coating device. FIG. 3 shows the magnetic coating liquid shown in Table 1 as the upper layer, the magnetic coating liquid shown in Table 2 as the lower layer, and a polyethylene terephthalate film having a thickness of 14 μm as a support by the coating apparatus of FIG. It is an example of the result of coating, orienting and drying on top, calendering, and measuring the coating film surface with a three-dimensional surface roughness meter.

In addition, in order to make it easier to see the convex portions on the surface of the coating film, the measurement results are output only in a portion higher than the average value in the height direction in the three-dimensional graphics.
Fine vertical stripes with a pitch of about 100 μm are recognized on the surface of the coating film in the running direction of the support. Furthermore, the average surface roughness (hereinafter abbreviated as RMS) of the coating film surface in FIG. 3 was 15.8 nm. When the electromagnetic conversion characteristics were measured using an M II format deck, the video band output (7 MHz) was -2 dB with respect to our standard tape, and the S / N ratio was -1 dB.

From the above, it is clear that the fine vertical stripes on the coating film surface as shown in FIG. 3 significantly reduce the electromagnetic conversion characteristics.

As a result of investigating the cause of the generation of the fine vertical stripes, the present inventor has found that the reason is as follows.
The magnetic coating liquid is unlikely to exist as primary particles due to the influence of the magnetic force between the magnetic powder particles, and forms a three-dimensional network structure. It is thought to be destroyed by the agglomerates it had (Painting Engineering, Volume 21, No. 10, pp. 475-479, 1986). Since the magnetic coating liquid that uses magnetic powder having a strong magnetic force and a small average particle size in the major axis direction has a very strong cohesive force, the agglomerates are applied while flowing on the order of several tens to 100 μm. The magnetic coating liquid is present in the liquid, and when this magnetic coating liquid is applied to the support by the coating device shown in FIG. 5, the agglomerate is pushed out from the slit of the coating device shown in FIG. It was found that vertical streaks occur because the surface is not sufficiently smoothed by.

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. At present, magnetic recording media are in the direction of high-density recording, and therefore magnetic powder of high magnetic force and ultrafine particles are used. The electromagnetic conversion characteristics such as N ratio were remarkably deteriorated, which was a fatal defect in product quality.

It is an object of the present invention to provide a coating apparatus for solving the above-mentioned problems and for manufacturing a magnetic recording medium having a multi-layer structure having a smooth coating film surface.

Means for Solving the Problems In order to solve the above problems, the coating apparatus of the present invention has three lips and two slits, and the lip tip cross-sectional shape on the downstream side of the slits is a curved surface. First
The slit side edge is A, the second slit side edge of the second lip is B, the anti-slit side edge of the third lip is C, and the angle between the tangent line X at A and the tangent line Y at B is θ1, and the tangent line Y is In the coating device satisfying 5 ° ≦ θ1 ≦ 45 ° and 5 ° ≦ θ2 ≦ 45 °, where the angle between the tangent line Z in C and the tangent line Z in C is θ2, the edge on the non-slit side of the third lip is in C and B. 2 mm, where α is the distance in the running direction of the support from the contact points D to C between the tangent line Y and the third lip
≦ α ≦ 6mm, and the third lip curvature radius R2 is 4mm ≦ R2
Upstream of the coating device such that the angle at which the support enters the coating device that is ≦ 20 mm is θ1 and the angle at which the support exits the coating device is θ2. It is characterized in that a support tool for the support is provided on each of the side and the downstream side.

Action The present invention has the above-mentioned structure, and immediately after the upper layer magnetic coating liquid extruded from the second slit is applied to the lower layer surface already applied on the support, the third lip surface allows the distance α In the meantime, high shear is applied to the upper layer magnetic coating liquid applied to the lower layer surface, and aggregates in the upper layer magnetic coating material are destroyed. Since the surface of the coating film is thus sufficiently smoothed, fine vertical stripes do not occur on the surface of the coating film.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a coating apparatus of the present invention. The tip cross-sectional shapes of the second lip and the third lip are curved surfaces, the second lip curvature radius R1 is within the range of 3 to 20 mm, and the third lip curvature radius R2 is within the range of 4 to 20 mm. The optimum radius of curvature of the lip curvature radius is selected according to the conditions of the viscosity of the magnetic coating liquid, the coating speed, the coating thickness, and the tension of the support. The thickness of the second lip and the third lip is in the range of 2-10 mm.

By using cemented carbide as the material for the three lips, the straightness and flatness of the lips can be finished in the order of several μm, and the second and third ties found when processing stainless steel or the like are further used. It was possible to prevent edge flash and sagging at the lip outlet end. As a result,
Even when a thin layer was applied, thickness unevenness did not occur in the width direction and vertical stripes on the surface of the coating film due to edge burrs and sagging did not occur, and good coating was possible.

The manifolds 6 and 7 penetrate in the coating width direction of the coating device. The cross-sectional shape of the manifold may be circular or semi-circular. The gap between slits 4 and 5 is usually 0.1 to 0.5 m
It is set to m, and the length in the width direction of the slit is almost the same as the coating width. The slit length from the manifold to the slit outlet is a viscosity considering the thixotropic property of the coating liquid,
The length is usually set to 20 to 100 mm, although it is set depending on the coating conditions such as the discharge amount from the coating device.

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

FIG. 2 is a sectional view showing a state in which the magnetic coating liquid is applied in two layers by the coating apparatus of the present invention.

The approaching angle of the support body 12 with respect to the present coating device is the same as the angle θ1 formed by the tangent line X and the tangent line Y shown in FIG. Set by roll. Further, a support tool provided on the downstream side of the third lip so that the angle at which the support body 12 exits the present coating device is the same as the angle θ2 formed by the tangent line Y and the tangent line Z shown in FIG. 14, set with guide rolls, for example.

The gap between the first slit side edge of the first lip and the support 12 is set to 5 to 200 μm. If the gap is smaller than this range, the support 12 and the edge of the first lip come into contact with each other due to the fluttering of the support 12 during traveling, and the support is scratched, which adversely affects the product quality. If the gap is larger than 200 μm, the air entrained in the support will be entrained and the coating will not be possible.

The edge on the second slit side of the third lip is provided with a step in the direction opposite to the support from the tangent line Y. The step is usually 5 to 50 μm
Set to. If the step is smaller than this, the magnetic coating liquid for the upper layer is scraped off by the edge of the third lip on the second slit side, and uniform coating cannot be performed. Further, if the step difference is larger than the above range, the magnetic coating liquid for the lower layer flows into the outlet of the second slit, so that the coating cannot be performed uniformly.

The magnetic coating liquid 10 for the lower layer is continuously supplied by the first pump 8 into the first manifold 6 in an amount corresponding to the amount applied to the support, and is pushed out to the first slit 4 by the liquid pressure in the first manifold 6. Further, the magnetic coating liquid 11 for the upper layer is continuously supplied into the second manifold 7 by the second pump 9 in an amount corresponding to the coating amount on the support, and is pushed out to the second slit 5 by the liquid pressure in the second manifold 7. .

In the lower layer magnetic coating liquid 10 extruded through the slits 4, there are aggregates of magnetic powder particles as described above. However, by setting the angle of the support with respect to the present coating apparatus as described above, the gap between the second lip surface and the support 12 is about twice the wet state lower layer coating film thickness, and the gap along the second lip surface. Is kept constant and the magnetic paint for the lower layer 10 to 10
^Since a high shear rate on the order of ⁵ to 10 ⁶ (1 / sec) is continuously applied, the agglomerates are finely broken and the coating film surface is smoothed. Therefore, fine vertical stripes on the surface of the coating film do not occur.

Further, the upper layer magnetic coating liquid extruded from the slit 5.
In 11 as well, there is an aggregate of magnetic powder particles as described above. However, as described above, by setting the angles of the support with respect to the present coating apparatus, that is, θ1 and θ2, a gap between the support 12 and the upper layer is formed between the points D and C on the third lip surface. And about twice the coating thickness in the wet state of the lower layer, it is kept constant along the third lip surface, and the high magnetic coating 11 has a high shear rate of the order of 10 ⁵ to 10 ⁶ (1 / sec). Since they are applied continuously, the agglomerates in the magnetic coating material for the upper layer are finely broken and the coating film surface is smoothed.

The research conducted by the present inventor has revealed that the size of α and the size of the third lip curvature radius R2 have a great influence on the smoothness of the coating film surface in two-layer simultaneous coating.

That is, when α is less than 2 mm, the distance or time for imparting high shear to the magnetic coating is shortened, so that the agglomerates cannot be sufficiently destroyed and fine vertical stripes are generated on the surface of the coating film. Further, if α is larger than 6 mm, the hydrodynamic resistance of the magnetic paint flowing through the gap between the support and the third lip becomes too large, and uneven film thickness occurs in the application width direction, making it impossible to apply. I also understood. Therefore, the distance α from the point D to the point C on the third lip surface is 2 mm ≦
Within the range of α ≦ 6 mm, it is possible to suppress the generation of fine vertical stripes on the coating film surface.

Further, the support tension set in the normal coating process is 100 to 400 g /
In the range of cm, when the third lip curvature radius R2 is smaller than 4 mm, the surface pressure from the support to the coating liquid flowing through the gap between the support and the third lip curved surface becomes too large,
Thickness unevenness in the coating width direction occurs and uniform coating cannot be performed. When R2 is larger than 20 mm, the surface pressure from the support to the coating liquid flowing in the gap between the support and the third lip curved surface becomes too small, and the effect of smoothing the coating film surface is lost, and Fine vertical stripes are generated on the membrane surface. Therefore, the third lip curvature radius R2 can be applied with a uniform film thickness within the range of 4 mm ≦ R2 ≦ 20 mm, and generation of fine vertical stripes on the coating film surface can be suppressed.

Example 1 The magnetic coating liquid shown in Table 1 as the upper layer magnetic coating liquid was discharged from the second slit so that the film thickness after drying was 0.3 μm, and the magnetic coating liquid shown in Table 2 was obtained as the lower layer magnetic coating liquid. The liquid was discharged from the first slit so that the film thickness after drying was 3.0 μm, and applied on a polyethylene terephthalate film having a support thickness of 14 μm. The coating speed is 100 m / min, and the support tension is 200 g / cm. In the coating device, coating was performed using a coating device in which the radius of curvature of the second lip was 15 mm, the radius of curvature of the third lip was 15 mm, and the value of α was changed as shown in Table 3.

After coating, aligning and drying, calendering,
A tape was prepared by slitting into a predetermined width.

In the case of α = 7 mm, uneven film thickness occurred in the coating width direction, and the coating could not be performed successfully. As a result of measuring the state of the coating film surface of each tape made with a coating device with α = 1,2,6 mm with a three-dimensional surface roughness meter, when α = 1 mm, the same fineness as shown in Fig. 3 was obtained. Vertical streaks occurred. The case of α = 2 mm is shown in FIG. 4 (a), and the case of α = 6 mm is shown in FIG. 4 (b).
As shown in FIGS. 4 (a) and 4 (b), fine vertical stripes (FIG. 3) found on the surface of the coating film when a conventional coating device is used.
Was not generated at all, and a very smooth coating film surface was obtained by the coating apparatus of the present invention.

Also, using the electromagnetic conversion characteristics of the tape prepared by using each coating apparatus according to this embodiment and the tape prepared by the conventional coating apparatus shown in FIG. 5, that is, the output at the video band frequency of 7 MHz by using the M II format deck. Table 4 shows the measurement results of the S / N ratio. The measurement of the electromagnetic conversion characteristics was shown by comparing the M II tape made by us with the reference tape. In addition, in Table 4, measurement was performed by a three-dimensional surface roughness meter.
RMS is also shown. The coating device according to the present invention, that is, a tape made with α = 2 and 6 mm, has a very smooth coating film surface, so that it is compared with a tape produced by applying with an α = 7 mm coating device or a conventional coating device. Then, it was found that the RMS was small, the reproduction output and the S / N ratio were remarkably excellent in level, and the effect of the present invention was remarkable.

Example 2 The magnetic coating solution shown in Table 1 as the upper layer magnetic coating solution was discharged from the second slit so that the film thickness after drying was 0.3 μm, and the magnetic coating solution shown in Table 2 was obtained as the lower layer magnetic coating solution. The liquid was discharged from the first slit so that the film thickness after drying was 3.0 μm, and applied on a polyethylene terephthalate film having a support thickness of 14 μm. The coating speed is 100 m / min, and the support tension is 150 g / cm. In the coating device, coating was performed using a coating device in which the radius of curvature of the second lip was 15 mm, the radius of curvature of the third lip was 5 mm, and the magnitude of α was changed as shown in Table 5.

After coating, aligning and drying, calendering,
A tape was prepared by slitting into a predetermined width.

As a result of measuring with a three-dimensional surface roughness meter the state of the coating film surface of each tape made with the above α coating device, when α = 1 mm, the same fine vertical stripes as shown in Fig. 3 were obtained. There has occurred. When α = 2 and 3.5 mm, a very smooth coating film surface similar to that shown in FIGS. 4 (a) and 4 (b) shown in Example 1 was obtained.

As in the case of Example 1, a tape prepared by using the coating apparatus according to this example and an electromagnetic conversion characteristic of the tape prepared by the conventional coating apparatus shown in FIG. Table 6 shows the output and S / N ratio measurement results and RMS at a band frequency of 7 MHz. The coating device according to the present invention, that is, the tape prepared with α = 2 and 3.5 mm, has a very smooth coating film surface, and therefore has a smaller RMS than a tape prepared by coating with a conventional coating device. It was found that the reproduction output and the S / N ratio were remarkably excellent in level, and the effect of the present invention was remarkable also in this example.

Example 3 The magnetic coating liquid shown in Table 1 as the upper layer magnetic coating liquid was discharged from the second slit so that the film thickness after drying was 0.3 μm, and the magnetic coating liquid shown in Table 2 as the lower layer magnetic coating liquid. The liquid was discharged from the first slit so that the film thickness after drying was 3.0 μm, and applied on a polyethylene terephthalate film having a support thickness of 14 μm. The coating speed is 100m / min. In the coating device, the size of α is fixed at 2 mm, the radius of curvature of the second lip is set to 15 mm, and the radius of curvature of the third lip is set.
Coating was performed using a coating apparatus in which R2 was changed as shown in Table 7.

After coating, aligning and drying, calendering,
A tape was prepared by slitting into a predetermined width. When R2 was 3 mm, uneven film thickness occurred in the coating width direction, and uniform coating could not be achieved. As a result of measuring the state of the coating film surface of each tape made with other R2 coating equipment with a three-dimensional surface roughness meter, when R2 is 21 mm, fine vertical stripes as shown in Fig. 3 Occurred. When R2 was 4 and 20 mm, a very smooth coating film surface was obtained as shown in FIGS. 4 (a) and 4 (b) shown in Example 1.

As in the case of Example 1, a tape prepared by using the coating apparatus according to this example and an electromagnetic conversion characteristic of the tape prepared by the conventional coating apparatus shown in FIG. Table 8 shows the output and S / N ratio measurement results and RMS at a band frequency of 7 MHz.

The tape produced by the coating apparatus of the present invention, that is, the tape with R2 = 4 and 21 mm, has a very smooth film surface,
Compared with a tape produced by coating with a 21 mm coating device or a conventional coating device, RMS is small, and both reproduction output and S / N ratio are remarkably excellent. Was also found to be significant.

Comparative Example Using the conventional coating apparatus shown in FIG. 5, the magnetic coating liquid shown in Table 1 as the magnetic coating liquid for the upper layer had a thickness of 0.3 μm after drying.
It is discharged from the second slit so that the thickness becomes m, and the magnetic coating liquid shown in Table 2 as the lower layer magnetic coating liquid has a film thickness of 3.
It was discharged from the first slit so as to have a thickness of 0 μm and applied onto a polyethylene terephthalate film having a support thickness of 14 μm. The coating speed is 100 m / min, and the support tension is 200 g / cm. After coating, orientation, drying, calendering, and slitting to a predetermined width to prepare a tape.

The results of measuring the coating film surface of the tape with a three-dimensional surface roughness meter are shown in FIG. Table 4 shows the electromagnetic conversion characteristics such as the output of 7MHz frequency and S / N ratio.

EFFECTS OF THE INVENTION As described above, according to the present invention, in coating a video tape having a two-layer magnetic layer, a magnetic powder having a strong magnetic force and a small average particle diameter in the major axis direction can be used to achieve a very high cohesive force. It became possible to coat the coating surface very smoothly with a strong magnetic coating liquid. As a result, the product quality of the multi-layered high density magnetic recording medium can be significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are sectional views showing an embodiment of a coating apparatus of the present invention, and FIGS. 3 and 4 show the surface roughness of a coating film three-dimensionally. FIG. 5 is a sectional view of a conventional coating device. 1 ... 1st lip, 2 ... 2nd lip, 3 ... 3rd lip, 4 ... 1st slit, 5 ... 2nd slit, 6 ...
First manifold, 7 ... Second manifold, 8 ... First pump, 9 ... Second pump, 10 ... Lower layer coating liquid, 11
...... Upper layer coating solution, 12 …… Support.

Claims (1)

[Claims] 1. A lip tip cross-sectional shape on the downstream side of the slit has a curved surface having three lips and two slits,
The first slit side edge of the second lip is A, the second slit side edge of the second lip is B, the anti-slit side edge of the third lip is C, and the tangent line X at A and the tangent line Y at B are set.
And the tangent line Z between the tangent line Y and the C line is θ1.
When the angle formed by and is θ2, 5 ° ≤ θ1 ≤ 45 ° 5 ° ≤ θ2 ≤ 45 ° The distance in the running direction of the support from the contact point D between the tangent line Y and the third lip at B to the above C is α. Is 2 mm ≤ α ≤ 6 mm and the third lip curvature radius R2 is 4 mm ≤ R2 ≤ 20 mm, the angle at which the support enters is θ1 and the coating device is With respect to the coating apparatus, a support tool for the support is provided on the upstream side and the downstream side of the coating apparatus so that the angle at which the support exits is θ2.