WO2004027151A1

WO2004027151A1 - A method for changing the running conditions of a curtain coater and an arrangement applying the method

Info

Publication number: WO2004027151A1
Application number: PCT/FI2003/000667
Authority: WO
Inventors: Heikki Vatanen
Original assignee: Metso Paper, Inc.
Priority date: 2002-09-20
Filing date: 2003-09-12
Publication date: 2004-04-01
Also published as: FI115546B; FI20021676A; AU2003260533A1; DE10393223T5; JP2005539155A; FI20021676A0; JP4217684B2

Abstract

The present invention relates to a method for changing the running conditions of a curtain coater (1). In the method, the impact angle (β) between a plane (Q) passing congruently with the direction of travel of a track comprised of a paper/board web (W) and a plane (P) passing congruently with the direction of travel of a coating curtain (F) hitting the impact point (I) of the paper/board web (W) is changed. The paper/board web (W) is supported by overhead support means (2) from above the paper/board web (W) at a point before the impact point (I), the layer of air on the upper side of the paper/board web (W) is removed by deaeration means (4, 4a) located in conjunction with the overhead support means (2). The paper/board web (W) is supported by underneath support means (3) from below at a point following the impact point (I), the impact point (I) being in the free drawing area (A) remaining between the points of support. To change the impact angle (β), the direction of travel of the track is changed within the free drawing area (A) by adjusting the location of the underneath support means (3). The invention further relates to an arrangement applying the method.

Description

A method for changing the running conditions of a curtain coater and an arrangement applying the method

The present invention relates to a method for changing the running conditions of a curtain coater, in which method the impact angle between a plane passing congruently with the direction of travel of a track comprised of a paper/board web and a plane passing congruently with the direction of travel of a coating curtain hitting the impact point of the paper/board web is changed.

The present invention further relates to an arrangement for changing the running conditions of a curtain coater, in which arrangement the impact angle between the direction of travel of a track comprised of a paper/board web and the direction of travel of a coating curtain hitting the impact point of the paper/board web is changed.

Curtain coaters used in paper and board machines apply a coating compound, paste or other substance suitable for coating on the surface of the paper/board web to be coated. The coating compound is fed through a wide nozzle, inclined surface or similar feeding means comprised in the curtain coater, from which the coating compound falls in curtain-like fashion onto a wide material web moving below the curtain coater nozzle.

In current machines, the application of coating compound is controlled to a great extent by changing the properties of the coating compound, whereby qualitative targets are not always met. As is well known, the running conditions can also be controlled through the discharge ratio between the coating compound and the web to be coated. However, in such cases the composition and properties (such as viscosity, density) of the coating compound impose limitations on running speed. At high speeds, especially at the impact point (point on the web onto which the curtain drips) between the curtain composed of the coating compound and the web, air may be trapped within the coating layer, thus impairing the quality of the coated product. At the impact point may, in addition, be formed a so-called heel, that is, the coating compound hitting the web may tend to spread in the opposite direction with respect to the direction of travel of the web. The curtain may also break before hitting the web.

There are devices available for removing the air travelling with the surface of a paper/board web, as disclosed in the patent application FI 19991863. It describes a doctor blade, which is located before the impact point in the direction of travel of the web, and the aim of which is to remove the air travelling on the surface of the web to improve the impacting of the curtain. This does not, however, eliminate problems resulting from the properties of the coating compound which appear during the coating stage, especially when coating at different discharge ratios of the coating compound and the web to be coated is desirable, for example, for different paper grades.

The aim of the present invention is to provide an invention by means of which the above-mentioned disadvantages can be eliminated or substantially reduced.

To achieve this aim, the method according to the present invention is characterised in that the paper/board web is supported by overhead support means from above the paper/board web, at a point before the impact point, the layer of air on the upper side of the paper/board web is removed by deaeration means located in conjunction with the overhead support means, and the paper/board web is supported by underneath support means from below, at a point following the impact point, the impact point being in the free drawing area remaining between the points of support, and that to change the impact angle, the direction of travel of the track is changed within the free drawing area by adjusting the location of the underneath support means.

To achieve this aim, the arrangement according to the invention is further characterised in that the arrangement comprises overhead support means for supporting the paper/board web from above the paper/board web, at a point before the impact point, the said overhead support means being provided with deaeration means for removing the layer of air on the upper side of the paper/board web, and underneath support means for supporting the paper/board web from below, at a point following the impact point, the impact point being in the free drawing area remaining between the points of support, and that the underneath support means are adjustable for changing the impact angle.

The advantage of this method and arrangement is that the impact angle can be changed by means of simple arrangements, and thus the behaviour of the curtain as it falls onto the web can be affected advantageously. Especially the formation of the so-called heel in the coating compound in the impact point area can be prevented. In such a case, as the discharge ratio between the web and the curtain increases or decreases (i.e. chiefly as the track speed of the web increases or decreases), the same coating compound can be used without having to compromise on qualitative aims. Also the composition of the coating compound may be changed without changing the track speed of the web, or changes in track speeds will at least be considerably smaller compared with the prior art.

Preferred embodiments of the present invention are disclosed in the dependent claims. The present invention is described in greater detail in the following, with reference to the accompanying Figure, which shows a diagrammatic view of an embodiment of the invention.

Accordingly, the Figure shows a view in principle of the arrangement according to the invention, which applies the method according to the invention. The actual curtain coater 1 is here located above the track (direction of travel indicated by an arrow) comprised of a moving paper/board web W. From here onwards in the specification, the term material web shall be used to denote the paper or board web. The lateral application nozzle la of the material web W is located at a distance from the material web W (so-called draining distance), so that coating compound can be applied or drained from it onto the surface of the moving web W. The coating compound to be applied forms a curtain F (or film) between the nozzle la and the web, the width of the curtain substantially corresponding to the width of the web W. The width of the curtain F may, however, be made somewhat wider than the web W, whereby a wet edge will be formed on the web to be coated. The width of the curtain F may also be made narrower than the web, whereby a dry edge is formed on the web to be coated. At the end of the free fall, the curtain F hits the surface of the material web W in the direction of the first plane P, at the so-called impact point I, from where the curtain F turns into the direction of travel of the material web W, thus forming a coating covering the surface of the web W. The free fall of the coating compound and its direction of travel at impact point I are here described as being essentially parallel with the vertical plane P, but they may naturally deviate from this. The material of the material web W is paper or board.

The arrangement comprised in the curtain coater 1 includes overhead support means 2 and underneath support means 3 for supporting the material web W. The overhead support means 2 are fitted to a location before the impact point I with respect to the direction of travel of the web W. The overhead support means 2 include a surface, which is against the material web W and formed into a suction surface to provide sufficient support. The part of the suction surface closest to the impact point I is fitted as close as possible to the impact point I. The overhead support means may be comprised of other types of means, such as a deflection box. On its surface are arranged fans by means of which an air cushion is formed between the surface and the material web W.

At the same time, the overhead support means 2 disintegrate the layer of air on top of the material web W. The disintegration and removal of the layer of air is in addition facilitated by deaeration means 4, 4a arranged in conjunction with the overhead support means 2 or in the overhead support means 2, the said deaeration means comprising an elongated doctor blade means 4 in the lateral direction of the material web W. The elongated doctor blade means 4 is located transversely with respect to the direction of travel of the web W, in conjunction with the overhead support means 2, before the impact point I, on the surface which is against the material web W, at a short distance from the impact point I. This distance corresponds essentially to the distance between the upper support means 2 and the impact point I. A new layer of air is unable to form on the surface of the web W over a distance of travel corresponding to this distance. The said distance is typically about 3 to 8 cm, for example, 5 cm. The distance required depends on the speed and surface quality of the material web W. The doctor blade means 4 further comprises a duct, which is connected to a suction duct 4a, through which the layer of air on the material web W is removed.

The underneath support means 3 are located at a point after the impact point I with respect to the direction of travel of the web W. The underneath support means 3 may consist of a roll 3, the shell of which forms a support plane on which the material web W is supported from below (i.e. on its uncoated side), as shown in the example. The underneath support means 3 may consist of some other support plane or the like, which comprises means supporting the web, for example, a deflection box as described above. Since the supporting roll 3 is located at a point following the impact point I in the direction of travel of the web W, between the overhead support means 2 and the underneath support means 3 remains a free drawing area A for the material web W. The length of the free drawing area A is a distance longer than the distance between the part of the overhead support means 2 or deaeration means 4 closest to the impact point I, and the impact point I. Therefore, the impact point I is in the free drawing area A. In the free drawing area A, the material web W is tight, which dampens disadvantageous vibration otherwise possibly generating on it.

As shown in the accompanying Figure, the curtain F drips onto the impact point I on the material web at angle β with respect to the direction of travel of the second plane Q passing congruently with the free drawing area A of the material web W. This angle β is the so-called impact angle. By changing the location of the underneath support means 3, the direction of travel of the material web W can be changed and thus the impact angle β can be adjusted. For this purpose, actuating means 5 are arranged in conjunction with the underneath support means 3, by means of which the underneath support means 3 can be moved. These actuating means 5 comprise - preferably arranged in conjunction with the underneath support means 3 - a piston-type cylinder 5, or several functionally interconnected piston-type cylinders, on the ends of the piston rods of which are fixed the underneath support means 3.

When the piston rod is actuated, also the underneath support means 3 at the end of the piston rod will move. The piston-type cylinder 5 may also be arranged to turn about its mounting, for example, about the lateral swivelling axis of the track, whereby the position of the underneath support means 3 may be better adjusted. The actuating means 5 are fixed to the frame part of the curtain coater arrangement, which is not shown in the Figure. For moving the underneath support means 3 may obviously be provided structurally different means, or a device, for example, screw guides.

The Figure shows diagrammatically an example of the adjustment of the impact angle β. The impact angle β may be adjusted within the area between the smallest angle βi and the largest angle β₂ by altering the position of the underneath support means 3 by the actuating means 5. The adjustment may be carried out also during running. The position of the underneath support means 3 drawn in continuous line corresponds to the smallest impact angle βi, in which case the direction of travel of the material web W is preferably substantially to the side and diagonally upwards. The smallest angle βi obtainable by the curtain coater arrangement according to the invention is less than or equal to 90 degrees, preferably within the range from 25 to 90 degrees. In the example, this angle βi is approximately 73 degrees. The position of the underneath support means 3 drawn in broken line corresponds to the largest angle β₂, in which case the direction of travel of the material web W is to the side and diagonally downwards. This means that the largest angle βi obtainable by the curtain coater arrangement is greater than or equal to 90 degrees, preferably 90 to 155 degrees. In the example, this angle is approximately 130 degrees.

By changing the impact angle β in this way, the behaviour of the coating compound as it hits the surface of the material web W may be influenced. For example, when large amounts of coating and/or low web W track speeds are used, at the impact point I and in its area is more readily formed a "heel" (not shown) formed by the coating compound as the coating compound tends to spread in the opposite direction with respect to the direction of travel of the web W. In such a case it is advantageous to adjust the direction of travel of the web W, in the previously taught manner, diagonally downwards or at least to adjust the impact angle β between the said planes P and Q to be greater, whereby the coating compound is better guided in the direction of travel of the web W.

Furthermore, when small amounts of coating and/or high track speeds of the web are used, it is more likely that air will penetrate between the web W and the coating compound. In such a case it is advantageous to adjust the direction of travel of the web W diagonally upwards in a previously taught manner, or at least to adjust the impact angle β between the said planes P and Q to be smaller to avoid the penetration of air. Obviously the angles βi - β₂ used in the arrangement according to the invention usually depend on the track speeds of the web W used and on the properties of the coating compound. The direction of travel of the web W may obviously also be horizontal.

It should furthermore be noted that the draining distance between the feeding means 1 nozzle lb and the material web W does not change substantially as a result of the adjustment of the impact angle β. This facilitates for its part the controlling, adjustment or amendment of the coating conditions.

The present invention is not limited only to the said example, but the invention may be implemented within the scope of protection of the claims disclosed.

Claims

1. A method for changing the running conditions of a curtain coater (1), in which method the impact angle (β) between a plane (Q) passing congruently with the direction of travel of a track comprised of a paper/board web (W) and a plane (P) passing congruently with the direction of travel of a coating curtain (F) hitting the impact point (I) of the paper/board web (W) is changed, characterised in that the paper/board web (W) is supported by overhead support means (2) from above the paper/board web (W), at a point before the impact point (I), the layer of air on the upper side of the paper/board web (W) is removed by deaeration means (4, 4a) located in conjunction with the overhead support means (2), and the paper/board web (W) is supported by underneath support means (3) from below, at a point following the impact point (I), the impact point (I) being in the free drawing area (A) remaining between the points of support, and that to change the impact angle (β), the direction of travel of the track is changed within the free drawing area (A) by adjusting the location of the underneath support means (3).

2. A method as claimed in claim 1, characterised in that the impact angle (β) is 25 degrees to 155 degrees.

3. A method as claimed in claim 1 or 2, characterised in that the direction of travel of the paper/board web (W) in the free drawing area (A) is horizontal, diagonally upwards or diagonally downwards.

4. A method as claimed in any of the above claims 1 to 3, characterised in that the location of the underneath support means (3) is adjusted by actuating means (5) arranged in conjunction with the underneath support means (3).

5. A method as claimed in any of the above claims 1 to 4, characterised in that the track is supported on the overhead support means (2) by means of suction.

6. A method as claimed in any of the above claims 1 to 5, characterised in that the layer of air on the upper side of the paper/board web (W) is removed by means of suction ducts (4, 4a) arranged in conjunction with the overhead support means (2).

7. An arrangement for changing the running conditions of a curtain coater (1), in which arrangement the impact angle (β) between a plane (Q) passing congruently with the direction of travel of a track comprised of a paper/board web (W) and a plane (P) travelling via the direction of travel of a coating curtain (F) hitting the impact point (I) of the paper/board web (W) is changed, characterised in that the arrangement comprises overhead support means (2) for supporting the paper/board web (W) from above the paper/board web (W), at a point before the impact point (I), the said overhead support means (2) being provided with deaeration means (4, 4a) for removing the layer of air on the upper side of the paper/board web (W), and underneath support means (3), at a point following the impact point, for supporting the paper/board web (W) from below, the impact point (I) being in the free drawing area (A) of the paper/board web (W) remaining between the points of support, and that the underneath support means (3) are adjustable for changing the impact angle (β).

8. An arrangement as claimed in claim 7, characterised in that the angle (β) between the impact point (I) and the paper/board web (W) can be varied within the range from 25 degrees to 155 degrees.

9. An arrangement as claimed in claim 7 or 8, characterised in that the direction of travel of the paper/board web (W) in the free drawing area (A) can be changed to horizontal, diagonally upwards or diagonally downwards.

10. An arrangement as claimed in any of the claims 7 to 9, characterised in that the underneath support means (3) can be adjusted by actuating means (5).

11. An arrangement as claimed in claim 10, characterised in that the actuating means (5) are piston-type cylinders.

12. An arrangement as claimed in any of the above claims 7 to 11, characterised in that the distance between the impact point (I) and the point of the overhead support means (2) or deaeration means (4, 4a) closest to the impact point (I) is shorter than the distance travelled by the paper/board web (W), during which a layer of air is formed on the surface of the paper/board web (W).

13. An arrangement as claimed in any of the claims 7 to 12, characterised in that the overhead support means (2) comprise a suction surface for supporting the paper/board web (W).

14. An arrangement as claimed in any of the claims 7 to 13, characterised in that the deaeration means (4, 4a) are suction ducts.