JP2006247471A - Curtain coating method and curtain coating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate risks of web damage and web breaking and to surely prevent the occurrence of coating ununiformity due to the air entraining phenomenon in a curtain coating method for performing a coating by allowing free-falling liquid film to collide with a continuously traveling web. <P>SOLUTION: In the curtain coating method for performing the coating by allowing the free-falling liquid film to collide with a continuously traveling web, an endless belt 6 made of a porous material and traveling at the same speed in the same direction as the web 4 is pressed over the whole width of the front side of a liquid film collision part of the web 4 supported by a backup roll 5 in the web traveling direction and the vicinity of the back surface of the endless belt 6 in a position in contact with the web 4 is evacuated. It is preferable that the endless belt 6 is pressed to the web 4 by using 2 rubber rolls 8 arranged parallel to the backup roll 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a curtain coating method and a curtain coating apparatus for coating a liquid film that freely falls on a continuously running web, and more particularly to a curtain capable of preventing coating unevenness caused by entraining air together at the time of a liquid film collision. The present invention relates to a coating method and a curtain coating apparatus.

  Conventionally, various methods such as blades, rollers, air knives, and slide hoppers are known as methods for applying a coating solution to a continuously running web. Among these coating methods, the curtain coating method is a method in which a liquid film 3 that freely falls using a liquid supply nozzle 1 or the like is generated as shown in FIG. . In the trouble that occurs in this curtain coating method, the air in the vicinity of the surface of the web 4 is carried from the direction of arrow A in FIG. 1 to the place where the liquid film 3 and the web 4 collide (hereinafter referred to as a coating portion), Since the air has almost the same speed as the web 4, the air may enter between the web 4 and the liquid film 3. As a result, a problem that coating unevenness occurs occurred.

In the curtain coating method, this phenomenon is called an air entrainment phenomenon, and how it can be suppressed is a big problem of the curtain coating method. As a method of suppressing the air entrainment phenomenon, there is a case where air (hereinafter referred to as an air boundary layer) carried at the same speed as the web is stripped immediately before the coating portion. There have been various proposals so far. As one of the methods, there is a method of bringing a shielding member into contact with the web as shown in the curtain coating apparatus described in Patent Document 1. As another method, there is a method in which pressurized air is blown from an opening close to the web, or sucked in reverse, as in the method described in Patent Document 2.
Japanese Patent Laid-Open No. 10-277459 Japanese Patent Laid-Open No. 11-188298

  However, the former has a risk that the shielding member may damage the web surface and cause a quality defect, and the latter requires the member having the opening to be close to the web. There is a problem that there is a high risk of the web being trapped and breaking the web. In particular, the latter reduces the great merit that there is no risk of web breakage due to traps such as dust because the liquid supply nozzle is separated from the web, which is a feature of the curtain coating method. Therefore, an object of the present invention is to provide a curtain coating method and a curtain coating apparatus that can eliminate the risk of web damage and web breakage, and can reliably prevent the occurrence of coating unevenness due to an air entrainment phenomenon.

  In order to solve the above-mentioned problems, the invention of claim 1 is directed to a curtain coating method in which a free-falling liquid film is applied to a continuously running web and applied in a web traveling direction of a web supported by a backup roll. A moving body that travels at the same speed and in the same direction as the web is pressed across the entire width in front of the liquid film collision portion.

  According to a second aspect of the invention, in the curtain coating method of the first aspect, the moving body is an endless belt.

  According to a third aspect of the present invention, in the curtain coating method of the second aspect, the endless belt is formed of a porous material.

  According to a fourth aspect of the present invention, in the curtain coating method of the second or third aspect, the vicinity of the back surface of the endless belt in contact with the web is decompressed.

  The invention of claim 5 is the curtain coating method according to any one of claims 2 to 4, wherein the tension of the endless belt is in the range of 5 kgf / m to 40 kgf / m.

  The invention of claim 6 is the curtain coating method according to any one of claims 3 to 5, wherein the opening ratio of the endless belt is in the range of 20% to 50%.

  The invention of claim 7 is the curtain coating method according to any one of claims 2 to 6, wherein the endless belt is pressed against the web by two rubber rolls arranged in parallel with a backup roll. .

  According to an eighth aspect of the present invention, in the curtain coating method of the seventh aspect, the rubber hardness of the rubber roll is in the range of JIS 50 degrees to 75 degrees.

  The invention of claim 9 is the curtain coating method according to claim 7 or 8, wherein the roll diameter of the rubber roll is in the range of 80 mm to 200 mm.

  The invention according to claim 10 is a curtain coating apparatus that applies a liquid film that falls freely to a continuously running web, and covers the entire width in front of the liquid film collision part in the web traveling direction of the web supported by a backup roll. The moving body that travels in the same direction and at the same speed as the web is pressed.

  According to an eleventh aspect of the present invention, in the curtain coating apparatus according to the tenth aspect, the moving body is an endless belt.

  A twelfth aspect of the invention is the curtain coating apparatus of the eleventh aspect, wherein the endless belt is formed of a porous material.

  A thirteenth aspect of the invention is characterized in that, in the curtain coating apparatus of the eleventh or twelfth aspect, the vicinity of the back surface of the endless belt in contact with the web is decompressed.

  The invention of claim 14 is the curtain coating apparatus according to any one of claims 11 to 13, wherein the tension of the endless belt is in the range of 5 kgf / m to 40 kgf / m.

  According to a fifteenth aspect of the present invention, in the curtain coating apparatus according to any one of the twelfth to fourteenth aspects, the opening ratio of the endless belt is in the range of 20% to 50%.

  According to a sixteenth aspect of the present invention, in the curtain coating apparatus according to any one of the eleventh to fifteenth aspects, the endless belt is pressed against the web by two rubber rolls arranged in parallel with a backup roll. .

  According to a seventeenth aspect of the present invention, in the curtain coating apparatus of the sixteenth aspect, the rubber hardness of the rubber roll is in the range of JIS 50 degrees to 75 degrees.

  The invention of claim 18 is the curtain coating apparatus of claim 16 or 17, characterized in that the roll diameter of the rubber roll is in the range of 80 mm to 200 mm.

  As described above, according to the curtain coating method and the curtain coating apparatus of the present invention, the porous material travels at the same speed in the same direction as the web over the entire width in front of the liquid film collision portion in the web traveling direction of the web supported by the backup roll. By pressing an endless belt made of quality, it is possible to reliably prevent the occurrence of coating unevenness due to air entrainment, which is one of the troubles in curtain coating, without the risk of web damage or breakage. become.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view conceptually showing an example of a curtain coating method and a coating apparatus to which the present invention is applied. In the figure, the coating liquid is discharged from the liquid supply nozzle 1 to form a liquid film 3 that freely falls while supporting the film end by the edge guide 2. Below that, the web 4 supported by the backup roll 5 runs, and the liquid film 3 collides with the web 4 to become a coating film on the web 4. Here, the arrow A indicates that the air boundary layer is carried to the coating portion as the web 4 travels. If no measures are taken to remove the air boundary layer, the coating unevenness due to the air entrainment phenomenon is indicated. The occurrence of this cannot be prevented.

  In addition to the method using the liquid supply nozzle shown in FIG. 1, there is a method for forming a liquid film that falls freely using a liquid feeder called a slide hopper. In the case of this method as well, it is necessary to take measures to remove the air boundary layer in order to prevent the occurrence of coating unevenness due to the air entrainment phenomenon, which is the same as the case of the method of FIG. Therefore, the present invention has made it possible to remove the air boundary layer and reliably prevent the occurrence of coating unevenness due to the air entrainment phenomenon.

  FIG. 2 is a sectional view conceptually showing a first embodiment according to the coating method of claim 1 and the coating apparatus of claim 8. As shown in the drawing, a porous endless belt 6 (hereinafter referred to as a porous infinite belt) that presses in the same direction and at the same speed as the web 4 is pressed against the web 4 immediately before the coating portion. The air boundary layer on the traveling web 4 falls out to the back surface of the porous endless belt 6 through the holes of the porous endless belt 6 due to the contact pressure received from the porous endless belt 6. Accordingly, there is no air boundary layer that causes an air entrainment phenomenon on the web 4 leading to the coating portion, and the occurrence of coating unevenness can be prevented.

  The perforated endless belt 6 is driven by a single drive mechanism (not shown) and travels in the same direction and at the same speed as the web 4, so there is no risk of damaging the web 4. Further, even if dust is caught between the porous endless belt 6 and the web 4, the web 4 does not break. The tension of the porous endless belt 6 needs to be in the range of 5 kgf to 40 kgf per 1 m width. When the tension is lower than the range, sufficient contact pressure for pushing the air boundary layer to the back surface of the porous endless belt 6 through the holes of the porous endless belt 6 cannot be obtained, and there is a risk of causing an air entrainment phenomenon. On the other hand, when the tension is higher than that range, the porous endless belt 6 tends to be stretched or distorted, and a stable coating operation cannot be performed.

  Furthermore, the aperture ratio of the porous endless belt 6 needs to be in the range of 20% to 50%. When the aperture ratio is lower than the range, the resistance when the air boundary layer is pushed out to the back surface of the porous endless belt 6 is large, and the air boundary layer cannot be sufficiently removed, and there is a risk of causing coating unevenness. On the other hand, when the aperture ratio is higher than the range, the strength of the porous endless belt 6 is remarkably lowered, and elongation and distortion are easily generated, and a stable coating operation cannot be performed.

  FIG. 3 is a sectional view conceptually showing a second embodiment of the coating method of claim 2 and the coating apparatus of claim 9. As shown in the drawing, a suction member 7 is disposed in the vicinity of the back surface of the porous endless belt 6, and the suction member 7 sucks the vicinity of the back surface of the porous endless belt 6 so as to keep the pressure in the vicinity of the back surface low. Configured. Although not shown, the suction member 7 is connected to a pipe for sucking internal air and a suction device. In this way, by keeping the pressure in the vicinity of the back surface of the porous endless belt 6 low, the amount of air that the air boundary layer passes through the hole of the porous endless belt 6 to the back surface of the porous endless belt 6 increases, and the air entrainment phenomenon The suppression effect increases.

  FIG. 4 is a sectional view conceptually showing a third embodiment according to the coating method of claim 5 and the coating apparatus of claim 12. As shown in the figure, rubber rolls 8 are disposed inside the porous endless belt 6 and in front of and behind the suction member 7. The rubber roll 8 supports the porous endless belt 6 and presses the porous endless belt 6 toward the web 4 side. As a result, the adhesion between the porous endless belt 6 and the web 4 is increased, and the amount of air that the air boundary layer passes through the holes of the porous endless belt 6 to the back surface of the porous endless belt 6 increases, thereby suppressing the air entrainment phenomenon. Increase.

  In addition, the rubber hardness of the rubber roll 8 needs to be in the range of JIS 50 degrees to 75 degrees. If it is softer than that range, the distortion of the rubber roll 8 due to the transport tension of the perforated infinite belt 6 increases, and the meandering of the perforated infinite belt 6 is induced to prevent stable transport. On the contrary, when the rubber hardness is harder than the range, the adhesion between the porous endless belt 6 and the web 4 is lowered.

  Furthermore, the diameter of the rubber roll 8 needs to be in the range of φ80 mm to φ200 mm. When it is smaller than the range, the roll is likely to be bent, and the adhesion between the porous endless belt 6 and the web 4 is lowered. In addition, the porous endless belt 6 is repeatedly bent with a large curvature, and the life of the porous endless belt 6 is extremely shortened. On the other hand, when the roll diameter is larger than the range, the distance between the rubber rolls 8 is increased, and the contact area between the porous endless belt 6 and the web 4 between the rubber rolls 8 is increased. The contact pressure to the web 4 is reduced, the force for pushing the air boundary layer to the back surface of the porous endless belt 6 is reduced, and the air boundary layer cannot be sufficiently removed.

Examples are given below for the purpose of further clarifying the present invention.
The coating solution is a solution having a viscosity of 25 mps as the following components.
Polyvinyl alcohol 7.0 parts by weight Calcium carbonate particles 5.0 parts by weight Water 88.0 parts by weight On a 50 μm-thick polyethylene terephthalate film running at a speed of 300 m / min using the curtain coating apparatus shown in FIG. / M ² was applied. As a result, there was no occurrence of coating unevenness due to the air entrainment phenomenon. Further, there was no web damage or web breakage due to dust. At this time, a porous endless belt 6 having an aperture ratio of 38% was used and driven with a tension of 20 kgf / m. The atmospheric pressure in the vicinity of the back surface of the porous infinite belt 6 was kept at -300 mmAq. Further, two rubber rolls 8 having a hardness of JIS 60 degrees and a diameter of 120 mm were used.

  In addition, as a comparative example with respect to the above-described example, in the curtain coating apparatus having no mechanism excluding the air boundary layer shown in FIG. Occurred frequently.

  In the present invention, in the production of printing paper, pressure-sensitive recording paper, heat-sensitive recording paper, photographic paper, printing plate making material, etc., a liquid coating material is applied at a high speed to webs such as continuously running paper, coated paper, and film. It is available when you want to.

It is sectional drawing which showed notionally an example of the curtain coating method and coating device with which this invention is applied. It is sectional drawing which showed notionally 1st Embodiment which concerns on the coating method of Claim 1, and the coating device of Claim 8. It is sectional drawing which showed notionally 2nd Embodiment which concerns on the coating method of Claim 2, and the coating device of Claim 9. It is sectional drawing which showed notionally 3rd Embodiment which concerns on the coating method of Claim 5, and the coating device of Claim 12.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid supply nozzle 2 Edge guide 3 Liquid film 4 Web 5 Backup roll 6 Endless belt (porous infinite belt)
7 Suction member 8 Rubber roll

Claims (18)

In the curtain coating method of applying a liquid film that falls freely on a continuously running web,
A curtain coating method characterized by pressing a moving body that travels in the same direction and at the same speed as the web over the entire width in front of the liquid film collision portion in the web traveling direction of the web supported by the backup roll. The curtain coating method according to claim 1,
The moving body is an endless belt. The curtain coating method according to claim 2,
The curtain coating method, wherein the endless belt is made of a porous material. In the curtain coating method of Claim 2 or 3,
A curtain coating method characterized by decompressing the vicinity of the back surface at a position in contact with the web of the endless belt. The curtain coating method according to any one of claims 2 to 4,
A curtain coating method, wherein the tension of the endless belt is in the range of 5 kgf / m to 40 kgf / m. In the curtain coating method in any one of Claims 3 thru | or 5,
The curtain coating method, wherein an opening ratio of the endless belt is in a range of 20% to 50%. The curtain coating method according to any one of claims 2 to 6,
The curtain coating method, wherein the endless belt is pressed against the web by two rubber rolls arranged in parallel with a backup roll. In the curtain coating method of Claim 7,
A curtain coating method, wherein the rubber roll has a rubber hardness in the range of JIS 50 to 75 degrees. The curtain coating method according to claim 7 or 8,
A curtain coating method, wherein a roll diameter of the rubber roll is in a range of 80 mm to 200 mm. In a curtain coating apparatus that applies a liquid film that falls freely to a continuously running web,
A curtain coating apparatus characterized by pressing a moving body traveling at the same speed and in the same direction as the web over the entire width of the web supported by the backup roll on the front side of the liquid film collision portion in the web traveling direction. The curtain coating apparatus according to claim 10,
The curtain applying apparatus, wherein the moving body is an endless belt. The curtain coating apparatus according to claim 11,
The curtain coating apparatus, wherein the endless belt is made of a porous material. The curtain coating apparatus according to claim 11 or 12,
A curtain coating apparatus, wherein the vicinity of the back surface of the endless belt contacting the web is decompressed. The curtain coating apparatus according to any one of claims 11 to 13,
A curtain coating apparatus, wherein the endless belt has a tension in a range of 5 kgf / m to 40 kgf / m. The curtain coating apparatus according to any one of claims 12 to 14,
The curtain coating apparatus according to claim 1, wherein an opening ratio of the endless belt is 20% to 50%. The curtain coating apparatus according to any one of claims 11 to 15,
The curtain coating apparatus, wherein the endless belt is pressed against the web by two rubber rolls arranged in parallel with a backup roll. The curtain coating apparatus according to claim 16,
A curtain coater characterized in that the rubber roll has a rubber hardness in the range of JIS 50 to 75 degrees. The curtain coating apparatus according to claim 16 or 17,
The roll diameter of the rubber roll is in the range of 80 mm to 200 mm.

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