JPH01184071A - Painting apparatus - Google Patents

Abstract

PURPOSE:To reduce variations of film thickness in the direction of the width of an obtained sheet without lowering electromagnetic properties, by tapering an exit part of a slit at least by a certain length and making the width of the edge of the exit 100mum or less. CONSTITUTION:A coating liquid is extruded continuously from a slit 3 between a front edge surface 1 and a back edge surface 3 on the surface of a running, flexible support to paint it. At least a certain area of the exit part of the slit 3 forms a taper between the wall surfaces 3A and 3B, and the angle theta1 of the taper is made within 3 deg.-10 deg. and the width of the edge of the slit is made <=100mum. As a result, the speed of the coating liquid in a prescribed flowing amount at the exit of the slit 3 is heightened and without lowering electromagnetic properties, variation of film thickness in the direction of the width of the obtained sheet is reduced. This apparatus is applicable to production of magnetic recording materials.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an extrusion type coating device, and particularly to a coating device that can obtain good coating when manufacturing magnetic recording media.

[Conventional technology]

It is well known that there are various coating methods such as roll coating, gravure coating, extrusion coating, slide bead coating, and curtain coating.

Magnetic recording media are obtained by coating a magnetic coating liquid on a support, and the coating methods generally include roll coating, gravure coating, and extrusion coating. Among these, extrusion coating is excellent because it provides a uniform coating thickness.

On the other hand, improvements in magnetic recording media themselves have progressed rapidly in recent years, and as a result, there has been a trend towards using oxidized magnetic powders and barium ferrite materials with high BET values, and coating liquids have become highly viscous. In addition, there is an increasing desire to perform thin film coating in order to cope with higher density, or to perform coating at the highest possible speed in order to increase productivity.

By the way, as a conventional technique in the extrusion coating method mainly aimed at manufacturing magnetic recording media, there are known techniques described in Japanese Patent Application Laid-open Nos. 57-84771, 5B-104666, and 60-238179.

[Problem that the invention seeks to solve]

Although the extrusion coating method described above can certainly obtain a uniform coating film thickness, it is only possible to obtain good coating conditions in a narrow range, and it is difficult to achieve high viscosity, thin film coating, and high speed coating as described above. Under these conditions, the desired application cannot be achieved.

In view of this, the present inventors conducted various experiments and studies, and found that in addition to the shape of the extruder, the fluidity of the coating liquid is a major controlling factor in this regard. I found out.

In particular, the fluidity of the coating liquid greatly affects the electromagnetic conversion characteristics.
In particular, it has been found that the flow rate of the coating liquid at the outlet of the coating liquid outflow slit is required to be higher than a certain condition. This condition is especially essential in the case of a coating liquid containing magnetic powder or metal powder with a BET value of 50 rrf/g or more.

Therefore, it is natural to think that in order to increase the flow rate under the conditions of the set film thickness and therefore the set coating liquid flow rate, the slit interval between the front edge surface and the back edge surface may be narrowed.

However, as described in each of the above publications, the slits of conventional coating devices are parallel, so narrowing the slit interval increases pressure loss at the slit portion, and moreover, pressure fluctuations during the process of passing through the slit portion are large. .

Under conditions exhibiting such a large pressure loss,
When used in conjunction with the coating liquid decoration shearing device shown in No. 62420, for example, when the slit interval is 50 μm or less, the pressure acting on the device will be 4 kg/cj or more, and the mechanical stress in each part of the device and liquid delivery system will be Trouble tends to occur in the seal part,
Furthermore, when forming slits, if the spacing between the slits is 50 μm or less, the machining accuracy of the slit surface will directly affect the slit surface, resulting in pressure fluctuations in the flowing coating liquid.

If there are pressure fluctuations due to the latter machining precision, or pressure fluctuations due to the constant slit spacing (it is difficult to make the pumping pressure uniform due to pressure pump pulsation, etc.), the coating liquid may flow irregularly from the slit outlet. As a result, this causes variations in film thickness in the machine direction and width direction of the sheet.

Therefore, the main object of the present invention is to provide a coating device that, in the case of a magnetic coating liquid, can provide sufficiently satisfactory electromagnetic exchange characteristics of the resulting magnetic recording medium, has little variation in film thickness, and has little pressure loss. It is about providing.

[Means for solving problems]

The above purpose is to continuously extrude a coating liquid onto the surface of a flexible support that runs continuously along the front edge surface and the back edge surface through slits between the front edge surface and the back edge surface. In an apparatus for applying a coating liquid, the slit is tapered over a certain length of at least the exit portion toward the exit end, and the angle at which the tapered surfaces intersect is 3° to 20°; This is achieved by setting the width between the ends to 100 μm or less.

[For production]

In the present invention, as shown in FIG.
are tapered, and the angle θ1 where they intersect is 3°
10", the flow velocity at the slit exit end is higher under a certain set coating liquid flow rate than when the slit surfaces are parallel. Therefore, the electromagnetic Given the fact that the flow velocity at the slit exit end is required to be above a certain value in order to avoid deterioration of the conversion characteristics, it is possible to obtain a sufficient flow velocity at the exit end, so that the desired electromagnetic conversion characteristics can be achieved. can be satisfied.

Further, if the wall surface of the slit is tapered, the pressure loss will be low, and even if the above-mentioned pre-coating shearing device is used, the pressure loss will be small, and troubles during its use will worsen. Furthermore, if the slit surfaces are parallel, if the processing accuracy of the entire slit surface is not high, there will be large variations in film thickness in the sheet width direction when coating. The film thickness variation in the sheet width direction depends only on the processing accuracy of the edges, and it is easy to maintain the desired processing accuracy only at the slit exit end, so as a result, the film thickness variation in the sheet width direction can be reduced. .

[Specific structure of the invention]

The present invention will be explained in more detail below.

FIG. 1 shows the main parts of the extruder according to the present invention, which has a front edge surface 1 on the upstream surface and a back edge surface 2 on the downstream surface, and a coating liquid pocket section (not shown) between them. It has a slit 3 that communicates with the lower part of the figure.

In the present invention, the wall surfaces 3A and 3B of the slit 3 form tapered surfaces, and the angle θ1 at which they intersect is 36 to 20 degrees. If it is less than 3°, the conventional problem cannot be avoided, and the
If it exceeds °, it is difficult to obtain a stable flow rate. In addition, it passes through the exit end interval width L of the slit 3, that is, the boundary edge between either or both of the edge surfaces 1.2 and the slit 3 (in the illustrated example, the boundary edge C with the back edge surface 2), and passes through the slit 3.
The distance measured in the direction perpendicular to the center NlAl4 is 1
00 μm or less, preferably 50 μm or less.

Further, it is desirable that the length H between the boundary edge C and a line drawn parallel to the line that passes through the downstream end B and is spaced apart satisfies H<L.

Note that, as shown by the imaginary lines in FIG. 1, the base side of the slit 3 is parallel, and the entire surface does not necessarily have to be a tapered surface.

On the other hand, the tangent J at the downstream end B of the front edge surface l,
Therefore, it is preferable that a part of the bank edge 2 protrudes (protrudes substantially upward in FIG. 1).

This condition is as follows: When the angle between the above l and the line 13 passing through the downstream end B and connecting the backing surface is α2, and the angle between the above II and the tangent 12 at the downstream end A of the backing surface 2 is α1, It can also occur as a condition of the following equation (2).

α2<α+<180° (2) On the other hand, the radius of curvature r of the backing surface 2 is preferably 3 to 10 degrees.

Also, the angle θ2 between the tangent line 12 and the wall surface is 80° to 1
10° is preferred.

As shown by the arrow, the support rises along the front edge 1, passes through the downstream end B, crosses the slit 3 and the liquid reservoir part 4, and goes around above the thickness of the coating liquid layer on the back edge surface 2. Go out to the right.

Examples of the support according to the present invention include a plastic film such as a polyester film, paper, a laminated sheet of both, a metal sheet, etc., and the material is not limited as long as it is a flexible material.

As a coating liquid, a magnetic coating liquid, especially 1000 cps (B
Although the effect of the present invention is noticeable when the present invention is applied to a magnetic coating liquid with a magnetic coating liquid of 60 rotations after 1 minute using a type viscometer, it is not applicable to a photographic photosensitive coating liquid or the like. Good too.

Further, when the coating speed is 150 m/min or higher, a remarkable effect can be obtained.

〔Example〕

Next, the effects of the present invention will be clarified in Examples.

A 15 μm polyester terephthalate film was used as a support, and a 3000 cps high viscosity magnetic coating liquid containing metal powder (BET value 60?/g) was applied to a wet film thickness of 30 μm to obtain a magnetic recording medium sheet.

In this case, the coating device according to the present invention and the
Prepare two coating devices with the coating device described in No. 238179,
The slit gap (the slit gap in the example is as above) is 50 μm and 100 μm, respectively. uf
fi, and the electromagnetic conversion characteristics of the obtained sheet RF out
, the film thickness variation in the width direction, and the pressure loss during coating were investigated, and the results shown in Table 1 were obtained.

Table 1 As shown above, according to the device of the present invention, the film thickness variation in the width direction is small and pressure loss is low without deteriorating the electromagnetic conversion characteristics.

〔Effect of the invention〕

As described above, according to the present invention, the variation in film thickness in the width direction of the obtained sheet can be reduced and the pressure loss can be reduced without deteriorating the electromagnetic conversion characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of a coating device according to the present invention. 1...Front edge surface, 2...Back edge surface,
3...Slit, 3A, 3B...Slit wall.

Claims (1)

[Claims] (1) A coating liquid is continuously extruded from the slits between the front edge surface and the back edge surface onto the flexible support surface that runs continuously along the front edge surface and the back edge surface. In an apparatus for applying a coating liquid to the slit, at least a certain length of the exit portion of the slit,
A coating device that is tapered toward its exit end, the angle at which the tapered surfaces intersect is 3° to 20°, and the width between the exit ends is 100 μm or less.