JPH11267569A - Slide curtain coating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a streak failure or the like hardly happen in a long-time continuous coating operation by making an angle formed by a lip surface and a lip tip face and a curvature radius at a connection part between the lip surface and the lip tip face specific values respectively, in a device of a construction that the lip surface and a lip back face are connected together by the lip tip face. SOLUTION: In the slid curtain coating device, a coating liquid B supplied to a coating die is spread, in a coat width direction, in the internal cavity of the die, and further, is formed into a thin coating film which is uniform in the coat width direction after passing through a slit. Further, the coating liquid B flows out over the sliding face of the die. In addition, the liquid B flows down a lip part and is separated from the die through a lip tip, freely falling, in the form of a curtain coating film, toward a web. In turn, the curtain coating film collides with the web to perform a coating process. Here, an angle formed by a lip surface C and a lip tip face E is set 120-150 deg. and a curvature radius R1 at a connection part between the lip surface C and the lip tip face E is set to be 100 μm. Thus it is possible to make to streak trouble and a point trouble hardly happen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slide curtain coating apparatus, and more particularly to a lip tip shape of the coating apparatus.

[0002]

2. Description of the Related Art Slide curtain coating is a coating method capable of simultaneously coating multiple layers and is a coating method well known to those skilled in the art. In this coating method, the coating liquid supplied to a slide hopper type coating die (hereinafter referred to as a die)
It is spread in the coating width direction in the cavity inside the die, and further passes through the slit to form a uniform thin film in the coating width direction and flows out to the slide surface of the die.

The slide surface is inclined with respect to the horizontal, and the coating liquid flows down the slide surface by the action of gravity. Further, the coating liquid flowing down along the lip provided as an extension of the slide surface and leaving the die from the lip tip becomes a thin falling free coating liquid film (hereinafter referred to as a curtain film), which is free toward the web. Fall. On the other hand, the web to be applied is moving at a high speed while maintaining a constant distance in the vertical direction from the tip of the lip, and the curtain film collides with the web to be applied.

Conventionally, a lip tip shape shown in FIGS. 2 and 3 has been known as a typical lip tip shape.

FIGS. 2 and 3 show that under certain coating conditions,
FIG. 4 schematically shows a cross-sectional view of a portion where the coating liquid flowing down from the lip is separated from the tip of the lip. A portion indicates a lip, and B portion indicates a coating liquid flowing down the lip. The surface C indicates the lip surface on which the coating liquid flows down, the surface D indicates the lip back surface parallel to the lip surface, and the surface E indicates the lip tip surface connecting the lip surface and the lip back surface. The angle formed by the surface E is denoted by α. Further, the connecting portion between the lip surface C and the lip tip surface E may be provided with a small radius of curvature as needed, and the radius of curvature at the connecting portion between the lip surface C and the lip tip surface E is indicated by R1. .

The flow of the coating solution in FIGS. 2 and 3 will be described. The coating solution flowing down the lip is separated from the lip tip surface E at a point F on the lip tip surface E (hereinafter, the point F is separated from the lip). A curtain film indicated by G is formed downstream from this point. The liquid separation point F is a point that can move along the lip tip surface E, and the position of the liquid separation point F on the lip tip surface E depends on the physical properties (viscosity, surface tension, etc.) of the coating liquid and the coating conditions (coating speed, Application amount).

FIG. 2 shows a case where α = 90 degrees.
Within the range of coating conditions used for normal curtain coating,
In the lip tip shape of FIG. 2, the leftmost end of the lip tip surface E is often the liquid separation point F. FIG. 3 shows a case where α is equal to or less than 90 degrees. The liquid separation point F moves to the right as α becomes more acute. However, a sharp lip tip shape with too small α increases the risk of tip breakage during operation, so α is kept at least 30 degrees and R1 = 50μ
It is common practice to provide a radius of curvature on the order of m to reduce the risk of tip breakage. When α is 30 degrees or more in FIG. 3, the liquid separation point F is often slightly to the left of the right end of the lip tip surface E in the range of application conditions used for normal curtain application.

In general, in order to efficiently produce a coated product, it is desirable that coating can be performed continuously for a long time without interruption. However, if continuous coating is performed for a long time over several tens of hours in the state shown in FIGS. A point-like coating failure (hereinafter, referred to as a point failure) is likely to occur, and in the state of FIG. 3, there is a problem that a continuous streak failure is particularly likely to occur over a long period of time. When the coating failure occurs,
Although the coating failure is eliminated by cleaning the tip of the lip, cleaning by interrupting the coating operation has significantly reduced production efficiency.

As described above, in the conventional lip tip shape, streak failures and point failures are likely to occur when continuous application is performed for a long time, and a lip tip shape in which these application failures are prevented has been desired.

[0010]

In view of the above problems,
An object of the present invention is to obtain a lip tip shape that prevents streak failures and point failures during long-time continuous application.

[0011]

An object of the present invention is to provide a slide curtain coating apparatus in which a lip surface through which a coating liquid flows and a lip back surface facing parallel to the lip surface are connected at a lip tip surface. The angle between the lip surface and the lip tip surface is 120 to 150 degrees, and
This has been achieved by a coating apparatus characterized in that the radius of curvature at the connection between the lip surface and the lip tip surface is at least 100 μm.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the conventional lip tip shape, a streak failure or a point failure may occur in a long-time continuous application. As a result of investigating the occurrence of these coating failures, the inventors of the present invention have found that partial coating stagnation near the liquid separation point F is the cause. Then, as a result of earnestly studying the lip tip shape in which this partial coating liquid retention was prevented, it was found that the lip tip shape of the present invention is effective in preventing the above-mentioned coating failure.

FIG. 1 shows a typical lip tip shape satisfying the claims of the present invention. FIG. 1 schematically shows a cross-sectional view of a portion where the coating liquid flowing down the lip surface C is separated from the lip tip under a certain coating condition, similarly to FIGS. 2 and 3. Α =
135 degrees, R1 = 200 μm. In addition, the flow of the coating liquid will be described. As in the case of FIG. 2, in the range of the coating conditions used for normal curtain coating, in the lip tip shape of FIG.
In many cases.

Here, the effect of the present invention on the flow of coating liquid and the occurrence of coating failure will be described by comparing FIGS. 2 and 3 in the case of the conventional lip shape and FIG. 1 in the case of the lip shape of the present invention. .

In the case of the conventional lip shape shown in FIGS. 2 and 3,
From the viewpoint of fluid dynamics, the coating liquid near the liquid separation point F tends to partially stay in the coating liquid, and this coating liquid retention causes the coating liquid to grow.

The reason will be described below. At the lip tip, the coating liquid is a very thin liquid film, and in particular, the liquid separation point F is a gas-liquid-solid static contact point in contact with both the solid lip tip and the gaseous ambient air. Therefore, the vicinity of the liquid separation point F is a portion where aggregation is likely to occur due to a partial temperature decrease due to heat conduction from the lip and the surrounding air and an evaporation of the solvent in the coating liquid by the surrounding air.

In addition, if the flow of the coating liquid in the vicinity of the liquid separation point F has a stagnation, the flow of the coating liquid itself has little self-cleaning action of washing out the agglomeration that has begun, so that the agglutination that has begun to grow. Cause. As described above, in the conventional lip tip shape, coating liquid aggregation easily occurs due to coating liquid stagnation near the liquid separation point F.

In the case of continuous coating for a long time, the coating liquid aggregation generated as described above sporadically flows down to a certain degree in the case of FIG. 2 and causes a point failure. Further, in the case of FIG. 3, since the generated aggregate is difficult to flow down and sometimes stays at the tip of the lip, the aggregate partially obstructs a part of the flow of the curtain film in the width direction, and the stripes are formed. It may cause a failure.

On the other hand, in the case of FIG. 1 of the present invention, since the vicinity of the liquid separation point F is a gas-liquid-solid static contact point, the condition that aggregation is liable to occur is the same as the conventional one. Mechanically, there is no stagnation in the coating liquid flow near the liquid separation point F,
Since the vicinity of the liquid separation point F is always purified by the flow of the coating liquid itself, the coating liquid does not actually aggregate. For this reason, it is possible to prevent point failures and streak failures during long-time continuous application.

As described above, it has been shown that, with the typical lip tip shape of the present invention, point failure and streak failure can be prevented in long-time continuous application.

Further, as described above, the range of α and R1 which can prevent point failure and streak failure in continuous coating for a long time was examined. As a result, α was 120 ° or more to prevent stagnation. is necessary. However, in a lip shape in which the lip surface C and the lip back surface D are parallel to each other, too large α sharpens the lip tip, and as described above, is not realistic because the risk of lip breakage increases. For this reason, the range of α is 120 degrees or more and 15 degrees or more.
0 degrees or less is an appropriate range. Also, for R1,
A somewhat large radius of curvature is required to prevent stagnation, and R1 of at least 100 μm is required for the above-mentioned range of α.

As described above, it has been shown that the use of the lip tip shape satisfying the claims of the present invention can prevent streak failure and point failure in continuous coating for a long time.

[0023]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Examples 1, 2, 3, 4, 5, 6 Using a slide curtain coating apparatus having α and R1 lip tip shapes shown in Table 1, using polyethylene-coated paper as a web, and using a gelatin aqueous solution as a main component The coating solution of the photographic emulsion was continuously applied for 24 hours under the following coating conditions and physical properties of the coating solution, and the coating conditions shown in Table 1 were obtained.

Slant angle of coating die: 23 degrees, coating speed: 150 m / min, WET coating amount: 60 g /
m ² , viscosity of coating solution; 50 cp, surface tension of coating solution; 25
dyn / cm

Comparative Examples 1, 2, 3, 4, 5, 6, 7, 8 Same as Examples 1 to 6 except that a slide curtain coating apparatus having a lip tip shape of α and R1 shown in Table 1 was used. When coating was continuously performed for 24 hours using the web, the coating solution, and the coating conditions, the coating conditions shown in Table 1 were obtained.

Measurement method and evaluation method for each item in Table 1 <Streak failure> The length of the failure portion in the coating flow direction is 1
A coating failure of not less than cm was defined as a streak failure, and a sample of the coated product was taken 24 hours after the start of coating, and the number of streak failures per sample area of 10 m ² was counted. <Point fault> A coating fault in which the length of the fault portion in the coating flow direction is less than 1 cm is defined as a point fault, and a sample of the coated product is collected 24 hours after the start of coating, and the sample area is 10 m ^2. The number of point failures per hit was counted.

[0028]

[Table 1]

Hereinafter, the results of the examples will be described in detail. As shown in Table 1, in Examples 1 to 6, α was 120 to 1;
This is an example in which R1 satisfies the range of 50 degrees and at least 100 μm. As can be seen from Table 1, streak failure,
Both point failures did not occur at all, and it was confirmed that the combination of α and R1 satisfying the claims of the present invention was effective in preventing streak failures and point failures.

On the other hand, Comparative Examples 1 and 3 are comparative examples in which both α and R1 were out of the range of the present invention, in which a streak failure and a point failure occurred. Further, Comparative Example 2 and Comparative Examples 4 to
5 is a comparative example in which R1 satisfies the claims of the present invention but α is out of the range of the present invention. In Comparative Examples 2 and 4, both a streak failure and a point failure occur. Only failure occurred. Further, Comparative Examples 6 to 8
Is a comparative example in which α satisfies the claims of the present invention, but R1 is out of the range of the present invention. No streak failure occurred, and only point failure occurred.

Thus, α satisfying the claims of the present invention.
Is particularly effective in preventing streak failures, but has not been completely prevented up to point failures. By combining R1 that satisfies the claims of the present invention, streak failures and point failures are completely prevented. I was able to confirm that I could.

[0032]

The use of the lip tip shape of the present invention has the effect of preventing the occurrence of streak failures and point failures during long-time continuous application.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a coating liquid flow when the lip tip shape of the present invention is used.

FIG. 2 is a schematic diagram of a coating liquid flow when a conventional lip tip shape in which α is 90 degrees is used.

FIG. 3 is a schematic diagram of a coating liquid flow when a conventional lip tip shape in which α is 90 degrees or less is used.

[Explanation of symbols]

A Lip tip B Coating liquid C Lip surface D Lip back E Lip tip F Liquid separation point G Curtain film α Angle between lip surface C and lip tip E R1 Curvature at the junction between lip surface C and lip tip E radius

Claims (1)

[Claims] In a slide curtain coating apparatus in which a lip surface through which a coating liquid flows and a lip back surface facing in parallel with the lip surface are connected at a lip tip surface, an angle between the lip surface and the lip tip surface is formed. 120-1
A slide curtain coating apparatus characterized in that the angle is 50 degrees and the radius of curvature at the connection between the lip surface and the lip tip is at least 100 μm.