EP1199404B2 - Method and device for calendering a web - Google Patents

Description

The invention relates to a method for smoothing a material web according to the preamble of claim 1. It further relates to a calender specified in the preamble of claim 15. Art and calender of this type are, for example, in the publications EP-A-0 957 202 and US-A-5 065 673 described.

Due to the high pressures acting on the calendering process and the simultaneous use of steam humidifiers and heated tempering rollers, the paper web is deprived of moisture during the calendering process or the paper is dried out. This drying can lead to an over-drying of the sheet structure with an insufficient residual moisture in the paper, whereby the calendering is adversely affected while the strength of the paper is greatly reduced.

In order to compensate for the moisture losses of the paper web during the calendering, the paper web must currently be moistened so far or less dried that it has a well-defined final moisture after calendering and before the pop roller or drum reel roller. This has previously been achieved by a single moistening by Düsenbefeuchtern before the calender and during the calendering process by the use of steam humidifiers. However, this steam humidifier can not fully compensate for the loss of moisture during the calendering, so that the paper web must be partially over-moistened by a Düsenbefeuchters depending on the calendering, the pressure and the distance between the dryer section and Poperoller.

The from the EP-A-0 957 202 and US-A-5 065 673 known calenders are equipped with the usual steam humidifiers for humidification and temperature control of the web. However, these steam humidifiers can not fully compensate for the moisture loss during the calendering process.

Also from the US-A-5 065 673 known calender again has the usual steam humidifier for humidification and temperature control of the web. To achieve the most uniform possible moisture profile of the finished paper web, an additional moistening device is provided following the calender between the latter and the reel.

The aim of the invention is to provide an improved method and an improved calender of the type mentioned, in which the aforementioned disadvantages are eliminated.

With regard to the method, this object is achieved according to the invention by the characterizing features of claim 1. It must therefore not necessarily be provided between each Nippaar an additional moistening unit.

Due to this configuration, a gradual remoistening of the material web results during the calendering process, with which now the moisture loss can be compensated. This allows a lower input moisture level in front of the calender, which reduces the variance of the moisture in the cross section. Ideally, by the moistening units used, the moisture expelled by the respective nip can be returned to the material web, so that in the following nip similar moisture conditions in the following nip again Material web prevail. Ideally, therefore, the input moisture of the web before the calender can be increased to the dry content required for the final quality. Moreover, the moistening of the material web can be reduced to the outermost web layers, whereby the compaction of the web is kept at the lowest possible level and still obtain a maximum calendering effect on the material web surface, so a so-called Totkalandrieren is avoided.

In a preferred embodiment of the method according to the invention, at least essentially only the water quantity removed from the material web by the respective nip is returned to the re-wetting points provided after a respective calender nip.

According to an expedient practical embodiment of the method according to the invention, a nozzle humidifier unit is used at a respective rewet body, which produces water droplets of a size which is smaller than about 30 microns and preferably in a range of about 1 to 30 microns.

In this case, for example, in each case a single-substance nozzle humidifier unit or, for example, also a two-substance nozzle humidifier unit can be used, in order in particular to produce a water / air mixture.

A respective remoistening effected by means of a nozzle humidifier unit can be assisted by an electrostatic charge of the material web. In principle, however, such rewetting by means of a nozzle humidifier unit can also be carried out without electrostatic charging of the material web.

In general, the use of the nozzle humidifier units serves to return the moisture vaporized by the hot calendering process to the material web surface. In this case, the contact time, which is dependent on the distance between a respective moistening point and the next nip and the material web speed, possibly the average Wasserropfgröße and the efficiency of water transfer to the material web is crucial. Possibly. can be further improved at a sufficiently high dry content by the use of the electrostatic charge of the web, the transfer of liquid droplets. As a result, in particular the most uniform moistening of the material web on the surface, comparable to a closed liquid film, is to be achieved.

According to an expedient embodiment of the method according to the invention, a quantity of water in a range from about 0.1 to about 5% by weight is returned to the material web surface at a respective rewetting point.

When rewetting is to be effected, the additional moistening and tempering of the material web by possibly provided steam humidifiers must be taken into account in order to achieve an optimum result.

There is at least one Rückbefeuchtungsstelle provided in the region of the web exit from the respective Kalandernip. This Rückbefeuchtungsstelle is directly at the web exit. In this case, there is the advantage, inter alia, that the surface moistening is assisted by the vacuum occurring in the region of the web exit.

However, for example, there are also the positions of the guide rollers before and after the calendering tips, which are not the subject of the invention.

According to an advantageous embodiment of the method according to the invention, the input moisture of the material web before the calender is at least substantially brought to the dry content required for the final quality.

In many cases, a transverse profiling of advantage. It is therefore expedient if at least one corresponding nozzle humidifier unit and / or at least one corresponding steam humidifier is provided for such a transverse profiling. It can be provided, for example, a regulation of the smoothness result and / or care for the most uniform possible moisture over the web width. Since a different evaporation (drying) is to be expected due to different line forces, a profiling, for example, would also be conceivable in the calender. In the foreground, however, is not the general regulation of the parameters, but much more important is the possibility of profiling.

In principle, it is also possible to use at least one additional guide roll as a pole (e.g., ground) for electrostatic charging.

In this case, the electrostatic charge may be provided, for example, in front of a respective guide roller. In the region of the respective guide roller, for example, a moistening unit can again be provided.

According to a further expedient embodiment of the method according to the invention is carried out in front of the calender remoistening with at least a nozzle humidifier and an electrostatic charge of the fibrous web with single-fluid and / or two-fluid nozzles.

For example, the moistening may be provided with additives which favorably influence the calendering process, e.g. the paper properties such as Improve shine and smoothness.

In the dependent claims further advantageous embodiments of the method according to the invention are given.

With regard to the calender, the object mentioned in the introduction is achieved according to the invention by the characterizing features of claim 15.

Advantageous embodiments of the calender according to the invention are specified in the subclaims.

Fig. 1

einen rein beispielhaften Trocknungs- und Bahntem- peraturverlauf von SC-Papier in einem herkömmlichen Kalander,

Fig. 2

eine rein schematische Darstellung eines Ausfüh- rungsbeispiels eines erfindungsgemäßen Kalanders, und

Filg. 3a, b)

nicht beanspruchte Anordnungen einer Befeuchtung mit elektrostatischer Aufladung.

The invention is explained below with reference to an embodiment with reference to the drawings. In this show:

Fig. 1

a purely exemplary drying and Bahntem- peraturverlauf course of SC paper in a conventional calender,

Fig. 2

a purely schematic representation of an embodiment of a calender according to the invention, and

Filg. 3a, b)

Unclaimed arrangements of electrostatic charging humidification.

FIG. 1 shows a purely exemplary drying and web temperature profile of SC paper in a conventional calender. On the abscissa of the diagram shown are several consecutively arranged in the web running measuring positions for the plotted on the left ordinate temperature or for the plotted on the right ordinate moisture content. The measuring positions 3 to 8 are inside the calender, the measuring positions 1 and 2 in front and the measuring positions 9 to 14 behind. In addition to the temperature measured in each case, the measured moisture directly before and the measured moisture immediately after the calender are indicated for the individual measuring positions.

As can be seen from the diagram, the steam humidifiers normally used can completely compensate for the loss of moisture during the calendering process. Accordingly, the paper web must be relatively heavily over-moistened by means of a jet humidifier before the calender or less dried in the dryer section. Accordingly, it can be seen from the diagram that the input moisture of the paper web in front of the calender is significantly above the moisture required for the final quality.

Fig. 2 shows in a purely schematic representation of an embodiment of a calender 10 according to the invention for smoothing a material web 12, which may be in particular a paper or board web.

The calender 10 comprises a plurality of nips 14 each formed between a pair of rollers, through which the material web 12 to be smoothed is guided. Before or behind the respective calendering tips 14 is the material web 12 led to guide rollers 18. Moreover, several steam humidifiers 18 are provided.

In addition, according to the invention a plurality in the web running direction L one behind the other, a respective distance from each other having Düsenbefeuchtereinheiten 20 are provided to backfeed the web of material L during its passage through the calender 10 at different in web running direction L consecutive points.

In the illustrated embodiment, the Düsenbefeuchtereinheiten 20 are arranged in the region of the respective web exit of the calendering tips 14, in each case directly to the respective web exit.

However, it is also possible, for example, to install an additional guide roller as a pole (earthing) of the electrostatic charge.

The nozzle humidifier units 20 at least substantially only the amount of water removed by the respective nip 14 from the material web 12 is returned or the expected moisture loss of the subsequent nip compensated.

Nozzle humidifier units will be used. These may in particular be designed to produce water droplets of a size which is less than about 30 microns and preferably in a range of about 1 to about 30 microns. In principle, both single-substance and dual-substance nozzle humidification units can be used. In particular, a water / air mixture is then produced with a respective two-substance nozzle humidifier unit.

In addition to a respective nozzle humidifier unit, means 22 for the electrostatic charging of the material web 12 can be provided in particular in order to support the humidification effected by the respective nozzle humidifier unit 20. In the FIG. 2 Such means 22 are merely indicated by way of example on the back moisturizing point located behind the first nip 14. In principle, however, such electrostatic charging means 22 may also be provided at other remoistening sites.

In the FIG. 2 are further, not inventive installation positions shown.

In each case, the nozzle humidifier units 20 may in particular be designed so that an amount of water in a range from about 0.1 to 5% by weight is delivered to the material web surface at the respective rewet bodies.

The Indian FIG. 2 illustrated calender 10 is inclined relative to the vertical. In principle, however, the calender 10 can also be oriented vertically. Apart from that, a calender divided into several stacks is also conceivable.

Basically, a Softglättwerk is conceivable.

In the case of the remoistening to be effected by means of the nozzle humidifier units 20, the additional moistening and temperature control of the material web 12 by the steam humidifier 18 provided must be taken into account.

The input moisture of the material web 12 in front of the calender 10 can at least essentially be brought to the dry content required for the final quality.

The FIGS. 3a) and 3b ) do not show arrangements according to the invention for moistening with electrostatic charging.

Again FIG. 3a ), at least a portion of the moistening units 20 may be provided immediately after a respective guide roller 16. The respective guide roller 16 can serve, for example, as a pole for an electrostatic charge.

According to FIG. 3b ), at least one additional guide roller 24 may be provided as a pole (eg ground) for electrostatic charging. This guide roller 24 are associated with corresponding means 22 for electrostatic charging. As based on the FIG. 3b ), the additional guide roller 24 is arranged in front of a guide roller 16. In the area of the guide roller 16, a moistening unit 20 is again provided.

It is also possible to provide at least one moistening unit, in particular at least one rewetted nozzle moistener 20 and / or electrostatic charging means 22, before the calender 10. In the present embodiment, the means 22 for electrostatic charging are preferably provided in the region of a guide roller 24, which can serve, for example, again as a pole for the electrostatic charge.

LIST OF REFERENCE NUMBERS

10

calender

12

web

14

calender nip

16

guide roll

18

Steam

20

Düsenbefeuchtereinheit

22

Means for electrostatic charging

24

Guide roller as pole of the electrostatic charge

L

Web direction

Claims (29)

1. A method of smoothing a material web (12), in particular a paper web or card web, by means of at least one calender (10) through whose nips (14) the material web (12) to be smoothed is guided, with the material web (12) being kept humid and at the right temperature by steam humidifiers (18) during staining and with moisture being removed from the material web during this satining,
   characterized in that
   the material web (12) is rehumidified during its run through the calender (10) by means of a respective additional humidifier unit (20) at a plurality of sequential positions in the web running direction (L) which have a respective spacing from one another directly at the web outlet from a respective calendar nip (14), in order to effect a stepwise rehumidification during the calendering process by which the loss of moisture is compensated.
2. A method in accordance with claim 1, characterized in that the material web (12) is rehumidified in the web running direction (L) after at least some of the nip passages, preferably after each nip passage.
3. A method in accordance with claim 1 or claim 2, characterized in that at least substantially only that amount of water removed from the material web (12) by the respective nip (14) is respectively added or returned at the rehumidification positions provided before or after a respective calender nip (14).
4. A method in accordance with claim 3, characterized in that a nozzle humidifier unit (20) is used which generates water droplets of a size which is smaller than approximately 30 µ m and preferably lies in a range from approximately 1 to approximately 30 µ m.
5. A method in accordance with claim 4, characterized in that a single-fluid nozzle humidifier unit (20) is used.
6. A method in accordance with any one of the claims 1 to 4, characterized in that a two-fluid nozzle humidifier unit (20) is used, in particular to generate a liquid (e.g. solution) / air mix.
7. A method in accordance with any one of the preceding claims, characterized in that a respective rehumidification effected by means of a nozzle humidifier unit (20) is supported by electrostatic charging of the material web (12).
8. A method in accordance with any one of the claims 1 to 6, characterized in that a respective rehumidification effected by means of a nozzle humidifier unit (20) takes place without electrostatic charging of the material web (12).
9. A method in accordance with any one of the preceding claims, characterized in that an amount of water in a range from approximately 0.1 to approximately 5 percent by weight is returned to the material web surface at a respective rehumidification position.
10. A method in accordance with any one of the preceding claims, characterized in that the humidification and temperature control of the material web (12) by the steam humidifiers (18) provided is taken into account in the rehumidification to be effected.
11. A method in accordance with any one of the preceding claims, characterized in that the ingoing moisture of the material web (12) before the calender (10) is at least substantially brought to the dry content required for the final quality.
12. A method in accordance with any one of the preceding claims, characterized in that at least one nozzle humidifier unit (20) and/or at least one steam humidifier for a transverse sectioning is provided.
13. A method in accordance with any one of the preceding claims, characterized in that at least one additional leading roll (24) is provided as a pole (e.g. ground) for electrostatic charging.
14. A method in accordance with any one of the preceding claims, characterized in that rehumidification takes place before the calender with at least one nozzle humidifier (20) and electrostatic charging of the fiber web with single-fluid and/or two-fluid nozzles.
15. A calender (10) for the smoothing of a material web (12), in particular a paper or card web, having a plurality of nips (14) through which the material web (12) to be smoothed is guided, and a plurality of steam humidifiers (18) for the moisturization and temperature control of the material web (12) during staining and with moisture being removed from the material web during this satining, in particular to carry out the method in accordance with any one of the preceding claims,
    characterized in that
    a plurality of additional humidifier units (20) are provided which lie behind one another in the web running direction (L) and have a respective spacing from one another to rehumidify the material web (L) during its run through the calender (10) at different positions sequential in the web running direction (L) in order to effect a stepwise rehumidification during the calendering process by which the loss of moisture is compensated.
16. A calender in accordance with claim 15, characterized in that a respective nozzle humidifier unit (20) is provided after at least some of the nips, preferably after each nip (14), in the web running direction (L).
17. A calender in accordance with claim 15 or claim 16, characterized in that at least substantially only that amount of water removed from the material web (12) by the respective nip (14) is respectively added by the nozzle humidifier units (20) provided after a respective calender nip (14).
18. A calender in accordance with claim 15, characterized in that the nozzle humidifier unit (20) is designed to generate water droplets of a size which is smaller than approximately 30 µ m and preferably lies in a range from approximately 1 to approximately 30 µ m.
19. A calender in accordance with claim 15 or claim 18, characterized in that a single-fluid nozzle humidifier unit is provided as the nozzle humidifier unit (20).
20. A calender in accordance with any one of the claims 15-18, characterized in that a two-fluid nozzle humidifier unit is provided as the nozzle humidifier unit (20) in particular to generate a liquid (e.g. solution) / air mix.
21. A calender in accordance with any one of the claims 15-20, characterized in that means (22) for the electrostatic charging of the material web (12) are provided in addition to a respective nozzle humidifier unit (20) in order to support the rehumidification effected by the spray or nozzle humidifier unit (20) and to accelerate the penetration into the web surface.
22. A calender in accordance with any one of the claims 15-21, characterized in that the nozzle humidifier units (20) are each designed such that an amount of water in a range from approximately 0.1 to approximately 5 % by weight is dispensed to the material web surface at the respective rehumidification positions.
23. A calender in accordance with any one of the claims 15-22, characterized in that it is inclined with respect to the vertical.
24. A calender in accordance with any one of the claims 15-23, characterized in that it is aligned at least substantially vertically.
25. A calender in accordance with any one of the claims 15-24, characterized in that it is divided into a plurality of stacks.
26. A calender in accordance with any one of the claims 15-23 or 25, characterized in that it is aligned substantially horizontally (e.g. soft smoothing works).
27. A calender in accordance with any one of the claims 15-26, characterized in that at least one additional leading roll (24) is provided as a pole (e.g. ground) for electrostatic charging.
28. A calender in accordance with any one of the claims 15-27, characterized in that at least one nozzle humidifier (20) serving for the rehumidification and means (22) for electrostatic charging are provided before the calender.
29. A calender in accordance with any one of the claims 15-28, characterized in that at least one nozzle humidifier unit (20) and/or at least one steam humidifier for a transverse sectioning is provided.

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