JPH03258368A - Coating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a coating apparatus for magnetic recording media used as magnetic tapes and floppy disks, and more particularly to a coating apparatus for simultaneously coating two layers.

BACKGROUND OF THE INVENTION As the performance of magnetic recording media has improved, the use of multiple magnetic layers has attracted attention in recent years. For example, by providing a magnetic layer with excellent high-frequency electromagnetic conversion characteristics for high-density recording as the upper layer, and a magnetic layer with low-frequency electromagnetic conversion characteristics as the lower layer compared to the upper layer, it is possible to achieve advantages that could not previously be obtained with a single layer. Excellent electromagnetic conversion characteristics can be achieved. Furthermore, in order to improve the adhesion between the magnetic layer and the support made of a plastic film, magnetic recording media are becoming more and more multilayered, such as by providing an anchor layer between the magnetic layer and the support.

It is desired that such a multilayered magnetic recording medium be manufactured by one-time coating and drying, and a coating apparatus for a multilayered magnetic recording medium is described in, for example, Japanese Patent Laid-Open No. 63-880.
It is disclosed in Publication No. 80 and the like.

Problems to be Solved by the Invention However, research by the present inventors has revealed that when a magnetic coating liquid for high-density recording is applied using the conventional coating apparatus, fine vertical streaks occur.

Figure 3 shows the magnetic coating liquid shown in Table 1 as the upper layer and the magnetic coating liquid shown in Table 2 as the lower layer applied to a polyethylene terephthalate film with a thickness of 14 μm as the support using the conventional coating apparatus shown in Figure 5. After being applied, oriented, dried, and calendered, the! ! ! This is an example of the results of measuring the film surface using a three-dimensional surface roughness meter.

(Margins below) Table 1 (Margins below) Table 2 The measurement results are shown in order to make it easier to see the convexities on the coating surface.
In three-dimensional graphics, only the portions higher than the average value in the height direction are output. v!
Fine vertical streaks with a pitch of about 100 μm are observed on the membrane surface in the running direction of the support.

Furthermore, the average surface roughness (hereinafter abbreviated as RMS) of the coating film surface in Figure 3 was 15.8n-.When the electromagnetic conversion characteristics were measured using an MU format deck, the video band output (7M) was obtained. tz), the result was -2 dB compared to our standard tape, and the S/N ratio was -1 dB.

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

As a result of investigating the cause of the occurrence of these fine vertical stripes, the inventors have found that it is due to the following reasons. It is difficult to think that the magnetic coating liquid exists as primary particles due to the influence of magnetic flux between magnetic powder particles, but forms a three-dimensional mesh structure, and when shear is applied to this, a certain It is thought that it is broken into aggregates with a certain size (V! Soukougaku, Vol. 21, No. 1O, pp. 475-479, 1986).

Magnetic coating liquids that use magnetic powder that has a strong magnetic force and a small average particle size in the long axis direction have very strong cohesive forces, so the agglomerates are on the order of several tens to hundreds of meters in size during flowing flow. When this magnetic coating liquid is applied to a support using the coating device shown in FIG. 5, the agglomerates are pushed out onto the lip from the slit of the coating device shown in FIG. It was found that vertical streaks occur because the surface is not smoothed sufficiently.

Furthermore, it has been confirmed through experiments that such fine vertical streaks appear more prominently when a magnetic coating liquid using magnetic powder having a stronger magnetic force and a smaller average particle size in the long axis direction is applied. At present, magnetic recording media are moving toward higher density recording, and for this reason, high magnetic force and ultrafine magnetic powder are used, so the fine vertical streaks on the surface of the coating film as described above are less likely to occur due to video band output or S/S. This significantly degraded electromagnetic conversion characteristics such as the N ratio, resulting in a fatal defect in product quality.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a coating apparatus for producing a multilayer magnetic recording medium with a smooth coating surface.

Means for Solving the Problems In order to solve the above problems, the coating device of the present invention has three lips and two slits, the tip of the lip on the downstream side of the slit has a curved cross-sectional shape, and the second lip has a The edge on the first slit side is A, the edge on the second slit side of the second lip is B, the edge on the anti-slit side of the third lip is C, and A
The angle between the tangent X at B and the tangent Y at B is θl,
When the angle between the tangent Y and the tangent Z at C is 02, in a coating device that satisfies 5@≦81≦45@ and 5°≦θ2≦45@, the edge of the third lip on the anti-slit side is When the distance in the running direction of the support from the point of contact between the tangent Y and the third lip at C and B to C is α, 2 legs≦α≦5−1, and the third lip curvature radius R2 is The configuration is such that 41≦R2≦20−.

Effect of the present invention With the above-described configuration, immediately after the magnetic coating liquid for the upper layer extruded from the second slit is applied to the surface of the lower layer already coated on the support, the magnetic coating liquid for the upper layer is applied by the third lip surface to Then, high shear is applied to the upper layer magnetic coating liquid applied to the surface of the lower layer, and the agglomerates in the upper layer magnetic paint are destroyed. Like this p! ! Since the film surface is sufficiently smoothed, fine vertical streaks do not occur on the paint film surface.

Example 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 device of the present invention.

The cross-sectional shapes of the distal ends of the second lip and the third lip are curved surfaces, and the radius of curvature R1 of the second lip is within the range of 3 to 20+w, and the radius of curvature of the third lip R2 is within the range of 4 to 20 mm. The optimum radius of curvature of the lip is selected depending on the conditions of the viscosity of the magnetic coating liquid, coating speed, coating film thickness, and support tension. The thickness of the second lip and the third lip ranges from 2 to 10 mm.

By using cemented carbide as the material for the three lips,
The straightness and flatness of the lip can be finished on the order of a few pm, and furthermore, it prevents the occurrence of crisp or sagging edges at the exit ends of the second and third lips that occur when processing stainless steel. did it. As a result, even when a thin layer was applied, there was no thickness unevenness in the width direction, and there were no vertical streaks on the surface of the coating film due to crisp edges or sagging, 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 either circular or semicircular, and the gap between the slits 4.5 is usually 0.1~
The length of the slit in the width direction is approximately the same as the coating width. The length of the slit from the manifold to the slit outlet is determined depending on the coating conditions such as the viscosity of the coating liquid in consideration of the thixotropic property and the amount of discharge from the coating device, but is usually 20 to 100 degrees long.

The tip shape of the first lip is planar in Fig. 1, but
Either a curved surface or a polygonal surface may be used.

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.

A guide roll (
(not shown). Further, the guide roller provided downstream from the third lip is set so that the angle at which the support body 12 comes out from the coating device is the same as the angle θ2 formed by the tangent line Y and the tangent line 2 shown in FIG. (not shown).

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 made smaller than this range, the support 12 and the edge of the first lip will come into contact with each other due to the flapping of the support 12 while it is running, causing scratches on the support, which will adversely affect product quality. If the gap is larger than 200 Ilm, air entrained in the support will be drawn in, making it impossible to coat.

The edge of the third lip on the second slit side is provided with a step in the direction opposite to the support from the tangent line Y. The zero step is usually 5 to 50 μm.
If the zero level difference set to is smaller than this, the magnetic coating liquid for the upper layer will be scraped off at the second slit side edge of the third lip, making it impossible to apply it uniformly. Furthermore, if the level difference is larger than the above range, the magnetic coating liquid for the lower layer will flow into the second slit outlet, making it impossible to apply it uniformly.

The magnetic coating liquid 10 for the lower layer is continuously supplied into the first manifold 6 by the first pump 8 in an amount equivalent to the amount to be coated on the support, and the liquid pressure in the first manifold 6 causes the magnetic coating liquid 10 to flow through the first slit 4.
is pushed out. 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 equivalent to the amount to be applied to the support, and is pushed out to the second slit 5 by the liquid pressure in the second manifold 7. .

As described above, aggregates of magnetic powder particles are present in the lower layer magnetic coating liquid 10 extruded through the slit 4. However, by setting the angle of the support with respect to the present coating device as described above, the gap between the second lip surface and the support 12 is approximately twice the thickness of the lower layer coating film in the wet state, and the gap is maintained along the second lip surface. Since the magnetic coating material 10 for the lower layer is continuously applied with a high shear rate on the order of 105 to 10' (17 sec), the agglomerates are finely broken and the tI! The membrane surface is smoothed. Therefore, fine vertical streaks on the surface of the coating film do not occur.

Further, the upper layer magnetic coating liquid 1 is pushed out through the slit 5.
1 also contains aggregates of magnetic powder particles as described above. However, by setting the angles of the support relative to the coating device, that is, θ1 and θ2, as described above, the gap between the support 12 and the upper The thickness of the coating film in the wet state of the lower layer is kept constant along the third lip surface, and the upper layer magnetic coating 11 has a coating thickness of 105 to 10' (1/5e
Since a high shear rate on the order of c) is continuously applied, the agglomerates in the upper layer magnetic paint are finely broken and the surface of the paint film is smoothed.

The inventor's research has revealed that the size of α and the size of the third lip curvature radius R2 have a large effect on the smoothness of the coating film surface in simultaneous application of two layers.

In other words, if α is less than 2, the distance or time to apply high shear to the magnetic paint becomes shorter, making it impossible to break down the agglomerates sufficiently, resulting in fine vertical streaks on the paint film surface. do. Furthermore, if the value of α is made larger than 6-, the hydrodynamic resistance of the magnetic paint flowing through the gap between the support and the third lip becomes too large, resulting in uneven film thickness in the coating width direction, making it impossible to coat. I also learned that. Therefore, the distance α from the dot on the third lip surface to point C is 2≦α
Within the range of ≦6, the occurrence of fine vertical streaks on the surface of the coating film can be suppressed.

Furthermore, the support tension set in the normal coating process is 100 to 40.
In the range of 0 g/as, the radius of curvature R2 of the 31st J.
If is smaller than 4, 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, causing uneven film thickness in the width direction of the coating, making it difficult to maintain uniformity. It becomes impossible to apply.

When R2 is larger than 20, 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 small, and the effect of smoothing the coating film surface is lost. Fine vertical streaks appear on the surface of the paint film. Therefore, the third lip curvature radius R2 is in the range of 4≦R2≦20 −, which allows coating with a uniform film thickness and suppresses the occurrence of fine vertical streaks on the surface of the coating film.

Example 1 The magnetic coating liquid shown in Table 1 as the magnetic coating liquid for the upper layer 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 used as the magnetic coating liquid for the lower layer. The coating liquid was discharged from the first slit so that the film thickness after drying was 3.0 am, and was applied onto a polyethylene terephthalate film having a support thickness of 14 μm. Coating speed is 100m/
min, and the support tension is 200 g/cm. Coating was carried out using a coating device in which the radius of curvature of the second lip was 15 degrees, the radius of curvature of the third lip was 15 degrees, and the size of α was changed as shown in Table 3.

Table 3 After coating, the tape was oriented, dried, calendered, and then slit to a predetermined width to prepare a tape.

In the case of α-7, uneven film thickness occurs in the coating width direction,
I couldn't apply it properly. As a result of measuring the condition of the coating film surface of each tape made with α-1, 2, and 6m coating equipment with a three-dimensional surface roughness needle, in the case of α=1, the same as shown in Figure 3 was obtained. Fine vertical streaks occurred. The case of α = 2 gardens is shown in Figure 4 (a), the case of α-6 gardens is shown in Figure 4 (a), and the case of using a conventional coating device as shown in Figure 4 (屹■) The fine vertical streaks (Fig. 3) that were observed on the surface of the coating film did not occur at all, and the coating device of the present invention made it extremely smooth! ! ! A membrane surface was obtained.

In addition, the electromagnetic conversion characteristics of the tapes made using each coating device according to this embodiment and the tapes made using the conventional coating device shown in FIG. and S/
The measurement results of the N ratio are shown in Table 4, and the electromagnetic conversion characteristics were compared using the MI tape prepared by our company as a reference tape. Table 4 also shows the three-dimensional surface roughness RMS measured using a needle. Therefore, compared to tapes made by coating with α-71 coating equipment or conventional coating equipment, the RMS is smaller, and both the playback output and S/N ratio are significantly superior, and the effects of the present invention are as follows. was found to be significant.

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

Table 5 After coating, the tape was oriented, dried, calendered, and then slit to a predetermined width to prepare a tape.

As a result of measuring the condition of the coating film surface of each tape prepared with the above-mentioned α coating equipment with a three-dimensional surface roughness needle, in the case of α-1m, there were fine vertical streaks similar to those shown in Figure 3. There has occurred. In the case of α-2 and 3.5 mm, very smooth coating surfaces similar to those shown in FIGS. 4(a) and 4(b) in Example 1 were obtained.

In addition, as in Example 1, the video band The measurement results of output and S/N ratio and RMS at a frequency of 7MI (z are summarized in Table 6).The tapes made with the coating apparatus according to the present invention, that is, those of α-2 and 3.5- Because the surface is very smooth, the RMS is lower than that of tapes coated with conventional coating equipment, and the playback output and S/
Both the N ratio and the level were extremely excellent, and it was found that the effects of the present invention were remarkable in this example as well.

(Margin below) Figure 4 Example 3 The magnetic coating liquid shown in Table 1 as the magnetic coating liquid for the upper layer was discharged from the second slit so that the film thickness after drying was 0.3 μm, and the magnetic coating liquid for the lower layer was The magnetic coating liquid shown in Table 2 was discharged from the first slit so that the film thickness after drying was 3.0 μm, and was applied onto a polyethylene terephthalate film support having a thickness of 14 μm. Coating speed is 100m/
It is mjn. Coating was carried out using an applicator in which the size of α was fixed at 2 mm, the radius of curvature of the second lip was 15 mm, and the radius of curvature R2 of the third lip was changed as shown in Table 7. Ta.

In the case of the 7th table, four minute lines appeared as shown in Figure 3. When R2 was 4 or 2'0, a very smooth coating surface was obtained as shown in FIGS. 4(a) and 4(b) in Example 1.

Further, as in Example 1, the electromagnetic conversion characteristics of the tape made using the coating apparatus according to this example and the tape made using the conventional coating apparatus shown in FIG. The measurement results and RMS of the output and S/N ratio at a band frequency of 7 MHz are summarized in Table 8.

(Margin below) After coating, it was oriented and dried, and after calendering, it was slit to a predetermined width to create a tape.

When R2 was 3-, film thickness unevenness occurred in the coating width direction, and uniform coating could not be achieved. As a result of measuring the condition of the coating surface of each tape made with other R2 coating equipment using a three-dimensional surface roughness meter, the R2 was 21. , the film surface is very smooth, so compared to tapes made by applying R2 using 21-kaku coating equipment or conventional coating equipment, R
It was found that the MS was small, and both the reproduction output and the S/N ratio were at extremely high levels, and the effects of the present invention were remarkable in this example as well.

Comparative Example Using the conventional coating apparatus shown in FIG. 5, the magnetic coating liquid shown in Table 1 was applied as the magnetic coating liquid for the upper layer to a film thickness of 0.3 after drying.
The magnetic coating liquid shown in Table 2 as the lower layer magnetic coating liquid was discharged from the first slit so that the film thickness after drying was 3.0 μm. It was coated on a polyethylene terephthalate film with a diameter of 14 μm. The coating speed was 100 m/min, and the support tension was 200 g/cm. v! After being oriented, dried and calendered, the tape was slit to a predetermined width.

Figure 3 shows the results of measuring the coating surface of the tape with a three-dimensional surface roughness needle.
Table 4 shows electromagnetic conversion characteristics such as N ratio.

Effects of the Invention As described above, according to the present invention, when coating a video tape with a two-layer magnetic layer structure, it is possible to apply a magnetic powder with a strong magnetic force and a small average particle size in the long axis direction. It is now possible to apply a highly magnetic coating liquid to a very smooth coating surface. As a result, the product quality of the multilayered high-density magnetic recording medium can be significantly improved.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing one embodiment of the coating device of the present invention, FIGS. 3 and 4 are explanatory views three-dimensionally expressing the surface roughness of the coating film surface, and FIG. 5 is a sectional view of a conventional coating device. 1...First lip, 2...Second lip, 3...Third lip, 4...First slit, 5......・Second slit, 6...First manifold, 7...Second manifold, 8
...First pump, 9...Second pump,
10... Coating liquid for lower layer, 1... Coating liquid for upper layer, 12... Support.

Claims (1)

[Claims] (1) It has three lips and two slits, and the cross-sectional shape of the tip of the lip on the downstream side of the slit is a curved surface, the edge of the second lip on the first slit side is A, and the edge of the second lip on the second slit side is B. When the edge of the third lip on the opposite side to the slit is C, the angle between the tangent X at A and the tangent Y at B is θ1, and the angle between the tangent Y and the tangent Z at C is θ2, 5 In a coating device that satisfies ゜≦θ1≦45゜5゜≦θ2≦45゜, when α is the distance in the support running direction from the point of contact D between the tangent Y at B and the third lip to the C, 2 mm. A coating device characterized in that ≦α≦6 mm and the third lip radius of curvature R2 satisfies 4 mm≦R2≦20 mm.