JP4572267B2 - Coating station and coating method - Google Patents

Description

[0001]
FIELD OF THE INVENTION
The invention relates to a spray coating station according to the preamble of claim 1 for coating a moving paper web, the spray coating station comprising a support roll, a spray applicator and doctor means, It relates to a spray coating station in which the web to be arranged is arranged to pass through said station, and further to a method for coating a moving web of paper or paper board.
[0002]
[Prior art]
The support roll used in the spray coating station has a diameter of about 1.3 meters, for example with its circumference manufactured with high circular accuracy. The function of the support roll is to support the web through the coating station so as to keep the distance between the applicator spray nozzle and the web maximally constant, thus keeping the quality of the deposited coating as constant as possible. At the doctor, the support roll forms a support surface against which the web is pressed by the doctor member. In order to ensure good coating results, the support roll is rotated at a speed that makes the tangential speed of the support roll surface substantially equal to the speed of the web.
[0003]
In accordance with convention, the web fed into the applicator device, the doctor means and the web applicator is such that the spray applicator nozzle is typically placed directly under the support roll and the web forms an acute angle of about 30-40 ° with respect to the horizontal plane. It is arranged in the spray coating station so as to be guided obliquely from above onto the support roll. A doctor means consisting of a blade, bar or air knife doctor is placed at a certain adhesion rest distance from the spray applicator nozzle in the direction of travel of the web.
[0004]
In the prior art of spray coating, problems have been caused by web bagging. Currently, the term sagging refers to the separation of the web from the support roll surface in the area between the spray applicator nozzle and the doctor member and in the area below the spray applicator nozzle. As a result, a bag-like shape occurs on the moving web. The sagging effect can reveal a bias in force balance at the coating station. At the doctor means, the web is pressed against the support roll under the linear pressure of the doctor member, so that the state is well controlled. Over the web length in front of the doctor point of action, the web is pressed against the support roll by the machine component of the web tension and the relatively small vector component of the coating spray impact applied perpendicular to the web surface. In practice, the force acting to pull the web away from the support roll typically exceeds the attraction force, thus causing the web to separate from the surface of the support roll.
[0005]
In the web area in front of the doctor, the web tends to be separated from the support roll by the force of the air pressure taken between the web and the support roll plus the centrifugal force applied to the paper web. The pulling force is mainly exerted by a large air layer traveling with the web surface moving at high speed. This large air mass cannot go into the nip under the doctor member by going through the web, but rather begins to accumulate between the web and the support roll. As the volume of accumulated air mass increases, the web bag holding the air also increases until equilibrium is reached, for example by spontaneous air release of the bag. At that time, air leaks through the edge of the bag. There is also a possibility that the amount of air carried by the web may be reduced by reducing the bag pressure when the front edge of the bag is opened. Centrifugal forces trying to move the web away from the surface of the support roll are effective at high web speeds and are proportional to the web speed, the basis weight and the bias angle of the web travel on the support roll. Obviously, the web is also subject to gravity.
[0006]
The sagging problem is raised by changing the distance between the web surface and the spray applicator nozzle. In the worst case, the bag can have a thickness of 20 to 30 mm, while the optimum distance from the web surface to the injection nozzle is in the range of 3 to 30 mm, often about 6 to 20 mm. This obviously adds complexity. In the central area in the cross machine direction where the sagging effect is worst, the web separates from the support roll until it touches the lip of the spray applicator nozzle. Eventually, the nozzle lip portion is worn rapidly due to the abrasion of the traveling web. In the middle cross-machine zone where the sagging web leaves the spray applicator nozzle but does not yet touch the surface of the support roll, the impact angle of the coating spray on the web will change. Such a change in impact point results in a back flow of the coating mixture. This in turn degrades the quality of the coating and increases the need for nozzle maintenance. Degradation of the coating quality is caused by the accumulation of coating aggregates on the nozzle lip , leading the coating spray away from the surface to be coated.
[0007]
[Problems to be solved by the invention]
It is an object of the present invention to overcome the disadvantages of the above technique, to provide a completely new type of spray coater station, and to provide a method for coating a moving web of paper or board.
[0008]
[ Means for Solving the Problems ]
The object of the invention is achieved by having the web enter the support roll of the spray coater station, just at or just before the spray coater nozzle. More particularly, the spray coater station according to the invention is characterized by what is stated in the characterizing part of claim 1, and the method according to the invention is characterized by what is stated in the characterizing part of claim 4. Is.
[0009]
The present invention provides significant benefits, i.e., the sagging effect at the spray coater nozzle is substantially reduced and the smoothness and quality of the coating is improved. Dirt on the applicator nozzle and wear on the lip at the top of the nozzle is reduced. The impact angle between the web to be coated and the coating jet remains constant throughout the cross-machine direction, thus making it easier to improve the control of the uncoated point and the generation of coating backflow.
[0010]
Overall, the present invention extends the service life of the spray coater station and provides a high quality coating with higher efficiency. In particular, the present invention improves the reliability of high speed and wide dressers and the performance of coaters with short downtime.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, a moving web 1 of paper or board and its path through a spray coating station are shown. In this embodiment of the invention, the web is guided to the support roll 2 by the guide roll 8. Thanks to the guide roll 8, the approach angle of the web 1 entering the support roll 2 can be selected within a large design tolerance. Supported by the support roll 2, the web 1 passes through the spray applicator 5 and continues to the doctor blade 6 . Finally, the web leaves the applicator station.
[0012]
FIG. 2 shows in more detail the principles of the invention and the basic instrument of this embodiment of the invention. The web 1 contacts the support roll 2 at the approach point 3. Assuming no bagging, the web 1 is substantially supported by the support roll 2 and continues to travel to the spray applicator 5. The coating spray discharged from the applicator strikes the web 1 at the impact point 7. From the jet impact point 7, the web continues to advance to the doctor blade 6 which is placed at a certain dwell distance, after which the web leaves the surface of the support roll 2 at the web release point 4. Led. In the embodiment shown, the web withdrawal point 4 is located on the doctor blade 6. The figure does not show the possible sag of the web 1 in the area between the spray applicator 5 and the doctor blade 6.
[0013]
To remove sagging, the web 1 passes tangentially over the support roll 2 at a location very close to the spray applicator 5 or slightly behind the applicator 5. The angle difference α between the web approach point 3 and the jet impact point 7 on the periphery of the support roll 2 is in the range of −5 to + 15 °, most preferably 0 to + 10 °. This angular difference is positive if the web approach point 3 is on the incoming side of the web 1 as viewed from the jet impact point 7 and if the web approach point 3 is on the leaving side of the web 1 as seen from the jet impact point 7. Defined as negative. In FIG. 2, the angle difference α is positive.
[0014]
In the embodiment of FIG. 1, the present invention is realized by providing a spray coater station with a separate guide roll 8 that serves to guide the web 1. Its web, close to contact with the substantially smaller angle with the supporting roll has a an observed et been more favorable, the supporting roll 2 from above obliquely at an angle of approximately 30 to 40 ° in a conventional manner. In a sheath design having a jet impact point 7 arranged to hit the web at a right angle at the lowest point of the support roll 2, the approach angle α of the web with respect to the horizontal plane and the relative height of the mounting position of the guide roll 8 are the above-mentioned guidelines. Can be easily determined according to.
[0015]
FIG. 3 shows a paper or board web 1 to be coated in connection with another embodiment of the spray applicator station of the present invention. In this embodiment, the web 1 enters the support roll 2 obliquely from above at an angle of about 30-40 ° with respect to the horizontal plane in a conventional manner. The angle difference α between the approach point 3 of the web 1 to the surface of the support roll 2 (FIG. 2) and the impact point 7 of the coating jet on the web (FIG. 2) is the vertical axis passing through the center point 9 of the support roll 2. The value specified in the present invention is controlled by placing the spray applicator 5 on the front side (with respect to the traveling direction of the web 1). This arrangement is different from the prior art. The relative position of the spray applicator is set so that the angle difference α falls within the range of −5 to + 15 °, most preferably 0 to + 10 °. The impact point 7 (FIG. 2) of the coating spray is then placed on the support roll 2 rotating with respect to the lowest point of the support roll 2 with a circumferential advance angle of 15-45 °. The doctor blade 4 is placed at a desired rest distance from the spray applicator 5.
[0016]
In addition to the above, other embodiments of the present invention are possible. Without deviating from the specifications of the invention, the web 1 is directed to the applicator station, for example at a different angle than that described above, and then the applicator station is appropriately positioned with respect to the selected approach angle of the web 1. The present invention can be applied. In one embodiment shown in FIG. 1, the web 1 enters the guide roll 8 at an angle of -5 to +5 [deg.], But the web 1 can also enter the support roll 2 in a vertical direction, for example, if desired. Also, existing papermaking machines exist by combining the use of the guide roll 8 of the web 1 and the arrangement of the spray applicator 5 different from the above-mentioned design with the applicator placed under the support roll 2 or as an alternative. It is also possible to arrange the web to be guided by moving the roll to a new position. Furthermore, the number or exact position of the guide rolls 8 is not limited. Therefore, the web 1 is guided vertically downwards to the support roll 2, for example over a higher guide roll 8 in the coater station, and the spray applicator is -5 to + 15 ° with respect to the horizontal plane of the support roll 2 , Preferably at an angle of 0 to + 10 °, respectively under the support roll 2 or in front of the web progression.
[0017]
Furthermore, the spray applicator 5 can also be placed in the applicator station so that the position of the applicator 5 can be changed. The position of the applicator 5 can then be advantageously adjusted by complementing the applicator station with a remote control actuator suitable for changing the position of the applicator 5 during deposition. The angular difference α can then be adjusted as required for the specific operating time coverage. When using a separate guide roll 8, the angle difference α can also be controlled by moving the position of the guide roll 8. Similarly, the position transfer of the guide roll 8 can be performed using the provided actuator means.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of one embodiment of a spray coater station of the present invention.
FIG. 2 is an enlarged cross-sectional view of a portion of the spray coater station shown in FIG. 1 placed near the web.
FIG. 3 is a cross-sectional view of another embodiment of the spray coater station of the present invention.

Claims (6)

The web (1) on the support roll (2) is arranged to support the web (1) moving around the support roll from the tangential approach point (3) of the web (1) to the tangential departure point (4) of the web. Supporting roll (2),
A spray applicator (5) for depositing a jet stream of the coating mixture at a spray impact point (7) on the surface of the web (1);
The doctor means for smoothing the deposited coatings as a jet onto the web (1) (6),
Including, in the injection coating station for coating a web (1) which is moving paper or paperboard,
When the positive direction of the angle (α) is defined to be opposite to the traveling direction of the web (1), the angular displacement along the roll periphery as seen from the center point (9) is the web approach point (3). Injection characterized in that the injection impact point (7) is placed substantially on the periphery of the support roll (2) at an angle (α) of -5 to + 15 ° between the injection impact points (7) Coating station (Figure 2). 2. Spray coating station according to claim 1, characterized in that at least one guide roll (8) is placed in front of a support roll and is adapted to allow the web (1) to enter the support roll (2). (FIG. 1). 3. A spray coating station (FIG. 2) according to claim 2, characterized in that the at least one guide roll (8) is adapted to cause the web (1) to enter the support roll (2) in a substantially horizontal direction. 1). The web (1) to be coated is advanced into the support roll (2), whereby the web (1) contacts the support roll (2) at the approach point (3),
Coating mixture in the form of a jet stream discharged from the jet nozzle (5) so as to hit the web surface at the jetting collision point (7) on the surface of the web (1) which is supported by the support roll (2) Is attached,
A method of coating a web (1) that the deposited film is formed by smoothed and care by a doctor means (6), moving the paper or paperboard,
When the positive direction of the angle (alpha) is defined to be opposite to the traveling direction of the web (1), the angular displacement along the circumference rolls viewed from the center point (9) of the web approach point (3) as the ejection impact point on the periphery of the substantially support roll (2) (7) is placed at a point at an angle of -5 to + 15 ° between the injection point of impact (7) (alpha), is coated A spray coating method (FIG. 2), characterized in that the web (1) to be driven is caused to enter the support roll. The web (1) to be coated is advanced over the guide roll (8) into the support roll (2), the path of the web (1) to be coated is deflected by the guide roll (8),
The position of the guide roll (8) is set to change the deflected travel path of the web (1) to be coated and an angular displacement (α) between the approach point (3) and the jet impact point (7) The spray coating method according to claim 4, wherein the spray coating method is adjusted in order to achieve the above . Injection according to claim 4, position characterized in that it is adjusted to vary the angular displacement between the web approach point (3) and the injection point of impact (7) (alpha) of the injector applicator nozzle (5) Coating method.

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